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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 [1] 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.[1] 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

  1. ^ http://www.space.com/25659-coldest-brown-dwarf-near-sun-discovery.html

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[1], 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

  1. ^ https://arxiv.org/pdf/1611.03495v2.pdf

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)

Image of orbit

I have removed the image of the orbit around Alpha Centauri because it gives the impression that from Earth it will appear like that. The truth is that in tens of thousands or hundreds of thousands of years, the system will move way off to the west. At different times during the orbit it will be at different places in the sky, eventually ending up north of the Milky Way between Lynx and Auriga. The view from Earth will also be from a different angle compare to now, so the orbit ellipse will change. The fact is that as Proxima and Alpha Centauri move, they trace wavy curves going west, rather than making ellipses in the sky. Eventually after a long time they will be so far away that the proper motion will be small and then their paths will start to look like loops or cycloids and then eventually like spirals, getting smaller and smaller as the system recedes. I tried to explain this with a brief note in the caption, but it was removed with the comment that I have to give references. Well, the alternative is just to remove this erroneous image, which I have now done. Please don't restore it unless you explain here why I'm wrong in what I have said. Eric Kvaalen (talk) 17:32, 10 January 2018 (UTC)

The shape of the orbit will indeed look like that. I'm putting the image back. The background is irrelevant, it isn't marking any landmarks. Tarl N. (discuss) 22:21, 10 January 2018 (UTC)


Orbital plot of Proxima Centauri.[1] This plot shows what the orbit looks like when the system is at its present position with respect to us. But in thousands of years, when Proxima will have moved further around the orbit, the system will have moved far to the west and Earthlings would see it from a different angle and with a different background.

@Tarl N.: I am putting the image with my caption here for reference. If you were to place an ellipse in space, moving along with the centre of gravity of the Alpha Centauri-Proxima system, then at this moment in time the ellipse would look like the one in the image. But of course the ellipse is moving with respect to us here in the solar system. By the time Proxima moves to the point marked 40 (40,000 years into the future), the ellipse will already have moved past the solar system. My guess, without doing a calculation, is that it will be somewhere near where Cancer, Hydra, and Canis Minor meet. "We", or any Earthlings around at that time, will see the ellipse from a completely different angle, so it won't look like the one in the image anymore.

If you were to draw the path of Proxima around the centre of mass of the system, as viewed from Earth, it would not look like an ellipse at all. It would look something like a spiral, first getting larger (in the distant past), and then getting smaller (in the distant future). At present it looks like Proxima is going counterclockwise around Alpha, but either in the distant past or in the distant future (I don't know which without doing a calculation) it would look like it was going clockwise around Alpha! The switch occurs when the plane of the orbit passses through the solar system. At that point in time, the orbit will or did look like a straight line segment!

Apparent and true orbits of Alpha Centauri. The A component is held stationary and the relative orbital motion of the B component is shown. The apparent orbit (thin ellipse) is the shape of the orbit as seen by an observer on Earth. The true orbit is the shape of the orbit viewed perpendicular to the plane of the orbital motion. According to the radial velocity vs. time the radial separation of A and B along the line of sight had reached a maximum in 2007 with B being behind A. The orbit is divided here into 80 points, each step refers to a timestep of approx. 0.99888 years or 364.84 days.

For a system like α Centauri A and B, it is legitimate to make an image like this one (used in the Alpha Centauri article), because the period is only 80 years, so they go around one another many times while we watch from an almost constant angle or viewpoint. But in the case of Proxima going around Alpha, this is not the case. The period is half a million years, but it only takes about a hundred thousand for the system to pass by us.

Look, I don't mind having the image be in the article, but if so it should have a caption like what I wrote.

Eric Kvaalen (talk) 07:45, 11 January 2018 (UTC)

I don't have a problem with the current caption because such plots are typically presented from the system's reference frame, rather than ours. However, the image background seems unnecessary and just serves as a distraction. It might be better to convert the image to a simpler SVG format. Praemonitus (talk) 16:06, 11 January 2018 (UTC)
Very much agreed with Praemonitus. The image presents great information, but the background is simply distracting. I wish I had any skills making SVGs, otherwise I'd make it myself. — Huntster (t @ c) 16:56, 11 January 2018 (UTC)
The background image serves to give a sense of scale of the orbit. When you have a photograph of α Centauri A and B, there are no background stars visible in the image - because at that magnification and brightness, nothing else appears. In this case, there are gobs of background stars in the image because the angular separation is so wide and the brightness so low for Proxima - which serves to provide a sense of scale. If there were any meaningful landmarks in the background image (beyond α AB and Proxima), there'd be a point in claiming confusion. But as is, I don't think the image confuses anyone. If that were a problem, no images of astronomical trajectories could ever contain any other stars, because everything moves all the time in different directions, and the background won't be precisely the same as the object moves. You couldn't even show a planet's motion against a stellar background, because those stars would have shifted by some tiny amount. I don't think this image is unreasonable. Tarl N. (discuss) 18:43, 11 January 2018 (UTC)
No, there's no sense of scale because you don't know how far away the viewing position lies. For me, all the background provides is a distracting clutter that delivers no additional information. As in art, less is more. If you need a sense of scale, then I'd suggest just using an actual scale − the number of light months, for example. Praemonitus (talk) 20:43, 11 January 2018 (UTC)
O.k. - I'll concede. As a stargazer, I feel it gives a significant feel for the scale (as in scale relative to the sky, not in physical meters), but if you're determined, find an image that gives just the ellipse. Tarl N. (discuss) 23:08, 11 January 2018 (UTC)
Tarl, we're not in a rush. Let's give it time to see what other opinions are out there. — Huntster (t @ c) 23:51, 11 January 2018 (UTC)
But would you feel the same sense of scale if the names were changed to Sun and Pluto? Praemonitus (talk) 18:58, 12 January 2018 (UTC)

@Tarl N., Praemonitus, and Huntster: But you're all ignoring what I said. It's not just that the background will change with time. It's that our viewing angle changes, and much more rapidly than Proxima goes around Alpha. Don't you agree? Eric Kvaalen (talk) 05:53, 12 January 2018 (UTC)

I did respond to that. Apparently you ignored it. Praemonitus (talk) 15:41, 12 January 2018 (UTC)


@Praemonitus: Sorry, but I don't know what you mean. Do you mean your sentence "I don't have a problem with the current caption because such plots are typically presented from the system's reference frame, rather than ours"? I don't understand that sentence.

At present, the Alpha Centauri/Proxima system is moving toward us with a velocity of 22.4 km/s and "sideways" (proper motion times distance) at 23.4 km/s, so the angle between its velocity vector and our present line of sight is arctan(23.4/22.4) or 46°. That means that in the next 28,000 years, as it comes to its closest point to us, the angle we see it at will change by 44°. The tangent changes by 22.4/23.4 every 28,000 years, so in the previous 275,000 years (half an orbit period) the angle changes by arctan((22.4/23.4)*(275/28)) or 84°, and in the next half a period it will change by another 84°. So while the system does just one orbit, the angle at which we see it changes by 168°!

Do you agree with that?

Eric Kvaalen (talk) 06:37, 13 January 2018 (UTC)

Yes, I agree that the position of the system is moving from our perspective. That would be a frame of reference centered on the Earth. For an orbital plot though, that is irrelevant. The image is being presented as though we are viewing it from a location that is co-moving with the Alpha Centauri system. Does that make sense? Praemonitus (talk) 23:34, 13 January 2018 (UTC)


@Praemonitus: Well if that's true then it should be explained in the caption. Actually though, this image, and others like it, are presented as viewed from Earth. It gives the false impression that in 40,000 years, Proxima will appear at the point marked "40", and in 80,000 years at the point marked "80" and so on, at least with respect to Alpha if not with respect to the background stars. Eric Kvaalen (talk) 06:40, 14 January 2018 (UTC)

@Eric Kvaalen: Orbital plots are pretty much always presented from the primary component's frame of reference. Otherwise all we'd see is a wiggly line of the proper motion that would be more difficult to interpret. Praemonitus (talk) 16:12, 14 January 2018 (UTC)


@Praemonitus: But the phrase "from the primary component's frame of reference" does not specify the view. In fact, it's not even clear what it means when you use it. It should mean a system of coordinates centred on the "primary component" (does that mean Alpha Centauri?). But to describe a view we need to specify a point from which we look at something, as well as the direction in which we look, which way is "up", what the scale is, and how all these things change with time if it's a "movie". Normally these orbit diagrams use the earth (or the solar system, let's say) as the viewpoint, and, as you say, we remove the proper motion, which is like turning our camera so that it's always pointing straight at the system. (The above image of the Alpha Centauri A & B system shows both this and also a view from a different point of view, showing the ellipse flat on.) Now, if we apply that to the Alpha/Proxima system, it means that we turn our "camera" by 168° while the system goes through one orbit. That means that the orbit gets rotated around some axis (not perpendicular to the orbital plane nor in the orbital plane) by 168° relative to the (rotating) line between us and the system. So even if we keep the system at the centre of our camera's view, the paths of Proxima and Alpha do not describe ellipses. (During the previous orbit, when the system was somewhere around Corona Austrina, it would not have moved nearly so much, but it would have drawn closer to us, so the orbit would have looked like it was getting bigger at the same time as rotating a few degrees. Overall, the system goes 180° around us, from Sagittarius to Centaurus where it is now and then on to Lynx or Auriga.)

The Alpha Centauri/Proxima system is unique in that it is the only one which is moving by us faster than the period of rotation. There are certainly other systems with periods of half a million years (though I don't think we actually know of any), but they would be far away and so would not move far through the sky during one period. There are also binary systems that are nearby (like Alpha itself, with A and B) and have a large proper motion, but they also have a relatively short period (80 years for Alpha). So in neither of these kinds of cases do we have the phenomenon that I am describing as the case for the Alpha/Proxima system -- slow period and high proper motion.

Do you agree with all this?

Eric Kvaalen (talk) 07:54, 15 January 2018 (UTC)

It comes down to common sense. You view the orbital plot from a position perpendicular to the plane, or else you end up distorting the elliptical shape. If you don't do it from that position, then it is necessary to present some symbols indicating the perspective. I don't see a need to clutter up the caption such obvious details, although I wouldn't be adverse to adding a footnote if the consensus is this is necessary. Praemonitus (talk) 15:49, 15 January 2018 (UTC)


@Praemonitus: Sorry, I don't understand what you're saying. You want us to show a plot from a position perpendicular to the plane? That's not what we have! By the way, viewing an ellipse from some arbitrary angle still gives an ellipse. That's not my point. My point is that we are trying to show the orbit from the perspective of the earth, but it gives the erroneous impression that in the future we (or whoever) will see Proxima in the positions marked, when in fact, the whole system will move by us before Proxima does even one orbit, and "we" will be looking at it from the other side! The image is totally misleading, and I don't see why we can't put in a longer caption to explain that this is not what one would see from the earth in the future. Eric Kvaalen (talk) 10:29, 16 January 2018 (UTC)

@Eric Kvaalen: No it's not. See the original image caption here. There's nothing that says it's seen from the perspective of the Earth. It's time to move past that. Praemonitus (talk) 00:52, 17 January 2018 (UTC)


@Tarl N., Praemonitus, and Huntster: I'm pinging the others for this. The image certainly is from the perspective of the earth. (The fact that the caption talks about the background stars is an additional confirmation. Also notice that Alpha is not near the focus of the ellipse, so it's certainly not looking at it from perpendicular to the orbital plane.) Take a look at Figure 1 in the article by Kervella et al, which is the source. They explicitly say that it's the view on the sky. Tarl and Huntster, what do you say? Eric Kvaalen (talk) 08:06, 17 January 2018 (UTC)

Well, if that were true, I'd say it's an overlay projection of the orbital plot on the background, rather than an expected future view. Praemonitus (talk) 17:31, 17 January 2018 (UTC)
Yeah, as best I can tell, it's a projection of the orbit as seen from earth. That's why I think the image as it stands is useful, it provides a sense of scale for the angular size of the orbit compared to the background - unusual for a multiple star, there are many other stars in the field of view. Note that "orbit" means the closed curve which the object moves on, which is distinct from actual trajectory traveled by the object (which could be a helix when you account for proper motion). We can project the entire closed curve of an orbit without requiring an object travel along it, which is what that image is doing. The year markers along the curve give an idea of just how slowly Proxima travels along that orbit. Tarl N. (discuss) 17:55, 17 January 2018 (UTC)


@Tarl N. and Praemonitus: Fine, but then let's explain in the caption that Earthlings will not see Proxima in the positions marked. Do we all agree on that fact now? Eric Kvaalen (talk) 09:20, 18 January 2018 (UTC)

You're making a mountain out of a molehill. That's like saying an image of a ship at sea needs to be caveated that the particular waves you see won't be there the next time you look at the ship. Tarl N. (discuss) 17:28, 18 January 2018 (UTC)
Nope. It would just add clutter with no particular benefit. Praemonitus (talk) 19:28, 18 January 2018 (UTC)


@Tarl N. and Praemonitus: I think it's an interesting fact, and I think that the present image is very misleading. It's not at all like talking about a ship going through different waves. (Remember, I'm not talking about the background.) You do realize that this system is different from all the others? In other cases, if you were to point a telescope at the system and put it on a mount that keeps it pointed at the system for tens of thousands of years, taking a movie, then if you watch the movie in fast motion, you would see both stars moving in near perfect ellipses. But in this case, it's not at all like that, at least not now. It was like that millions of years ago, and will be again millions of years hence. But now, from say half million years ago till half a million years from now, Proxima is not making ellipses around some moving point in the sky. Do you agree with that? Yet that is what the image implies. Eric Kvaalen (talk) 20:19, 19 January 2018 (UTC)

3000 words later, you haven't convinced me the image is misleading. I think it shows an orbit (an instantaneous closed curve, as opposed to a prediction of location) projected from the viewpoint of earth, against the current background of stars. I think the image is useful in showing the scale of the orbit as seen from earth. It does not show the future trajectory of either star, and would be misleading only if it identified particular landmarks and implied future location relative to such landmarks. Since you don't seem to be getting consensus, if you insist on changing this, you'll have to proceed through other means - WP:3O, WP:DRN, WP:M, ...
I do suggest that you re-read WP:WALLOFTEXT and keep that in mind. I've ignored several of your discussions on this and other pages because I simply didn't have the time to spend going through pages after pages of your arguments. Regards, Tarl N. (discuss) 02:05, 20 January 2018 (UTC)


It's all because of four lines of caption that I wanted to add to an image to clarify things. I still don't know whether you two have understood what I'm trying to say, because when I ask whether you agree with what I claim, you don't answer. Eric Kvaalen (talk) 08:09, 20 January 2018 (UTC)

  • I think the point deserves a little explanation, maybe not four lines. It would be nice if we had a diagram/plot of the projected proper motions of A/B & C for comparison, putting the orbit in scale with the space motion. However, what about captioning the present one something like Orbital plot of Proxima Centauri superimposed to scale on a recent photograph ? (Addition in bold.) That would alert readers to the distinction between the present-day appearance and the plot’s extension through time, without going into too much detail.—Odysseus1479 08:34, 20 January 2018 (UTC)
@Tarl N., Praemonitus, Huntster, and Odysseus1479: In private communication with one of the authors of the Kervella paper, he suggests that we say in the caption that the image represents the trajectory of Proxima relative to the barycentre of the system, projected on the plane perpendicular to the Sun-Alpha Centauri vector (the present "plane of the sky"), and that the marked time-points simply give an indication of the position of Proxima relative to AB in this plane. Eric Kvaalen (talk) 11:09, 20 January 2018 (UTC)
(TPW) I don't go around handing out barnstars and such, nor have I paid attention to every twist and turn of this saga, but I feel compelled to commend you for your efforts on this, Eric. You were absolutely right to pursue this issue and you've gone beyond the call of duty in your efforts to find the proper wording for the caption. I have to say, I'm impressed. nagualdesign 16:31, 20 January 2018 (UTC)
Given the mass distribution of this system, the barycentre is probably indistinguishable from the blur that is Alf Cen AB. So yes, it's a projection of the orbital plot as seen from the perspective of the Earth. I was mistaken in my initial assessment of thinking it was from a position perpendicular to the orbital plane. But to me that's a communication failure with the original ESO caption. That being said, I still see no reason to change the current caption. Possibly the wording on the image page needs revising. Praemonitus (talk) 15:58, 20 January 2018 (UTC)


@Tarl N., Praemonitus, and Huntster: So I'd like to know, do we agree on the facts? Do we all agree now that the image is from the point of view of the earth, that the system moves through a large angle in the sky as it executes the present half-million-year-long orbit, and that during the present orbit "we" see the elliptical orbit from many different angles and many different distances as the system passes us by? Eric Kvaalen (talk) 13:14, 22 January 2018 (UTC)

I honestly don't know how to react to all this. On one hand, as someone interested in this subject material I find the discussion interesting. But looking at it from a lay person's perspective, I'm honestly facepalming. I feel that's the key, here: the vast majority of our readership are laypersons who couldn't care one whit that the image won't be accurate in 28,000 years, or 40, or 80. They will find the image interesting because it represents what the system looks like from our perspective right now, and that perspective will not change in any meaningful way during our lifetimes. For educational purposes, it is absolutely appropriate to make sure that the change in perspective is explained in the prose, but the ratio of effort expended here thus far versus the value to the end user is unreasonable. Remember, WP:KISS, especially in the relatively limited space of an image caption. — Huntster (t @ c) 14:28, 22 January 2018 (UTC)
Amen. Tarl N. (discuss) 16:19, 22 January 2018 (UTC)
The current caption remains correct, does it not? It is brief and to the point. I think that further details can be made available on the image page or in a footnote, for the few readers who are interested. Praemonitus (talk) 18:57, 22 January 2018 (UTC)


Well, I still don't know the answer to my question of yesterday. But never mind. I agree that the ratio of effort to value was large. Originally Praemonitus objected that what I wrote was unsourced, which implies that he probably thought it was untrue. So I tried to convince him. Now he says the caption as it stands is correct -- true, but we should put things in that are interesting. I will make a footnote. Eric Kvaalen (talk) 14:35, 23 January 2018 (UTC)

Yes, my two remarks aren't contradictory. The original caption on the article still appears correct, and your preferred wording was unsourced. I didn't necessarily disagree with your position. It just seems a bit of a bunny trail that distracts from the core topic. Praemonitus (talk) 15:27, 23 January 2018 (UTC)
For what it's worth, I'd like to respond to the comment: Praemonitus objected that what I wrote was unsourced, which implies that he probably thought it was untrue.
NO.
Whether he thought it was untrue or not, unsourced comments are not allowed. Period. The whole point of Wikipedia is that we report what others have written (see WP:SECONDARY), and document where it has been reported. The idea is that a librarian should be able to maintain the articles, without needing to be an expert in all the subjects wikipedia covers. Writing the articles requires expertise. Precluding vandalism should not. And edits which don't document their source should be kept out. Even if accurate. Tarl N. (discuss) 22:42, 23 January 2018 (UTC)

Regarding the added footnote, please note that this is a featured article which means it is held to the highest standards for Wikipedia. That includes no original research or unnecessary vagueness. Vague relative words like 'far' should be clarified. How far? 100 km is far for me. However, numbers require citations for confirmation. If it can not be specifically referenced, then it should either be a quote from a notable individual or kept out. Participating in the WP:FAC process is a good way to get familiar with these types of requirements and to understand why they are subject to scrutiny. Praemonitus (talk) 19:22, 24 January 2018 (UTC)


@Praemonitus: You just reverted my edits. First you took the word "far" out of the sentence "In thousands of years, when Proxima has progressed further in its orbit, the system will have moved far to the west and Earthlings would see it from a different angle and with a different background", saying it was "vague". Then when I put in a more specific figure "about 70°", you reverted, complaining that I have no reference!

I think you're not acting in good faith. You do not own this article.

If you take out the word "far", then you remove the whole point. We have discussed this for the last couple weeks. Do you really not believe that it will move far to the west? Do I need to explain to you again why it's about 70°? Or do you understand, but you want to make sure I don't succeed in conveying this point to the readers? All this just about one little word! But an important word.

Eric Kvaalen (talk) 20:19, 24 January 2018 (UTC)

Then let me be clear: do not use relative terms, and do not add unsourced information, especially when it has been specifically challenged. — Huntster (t @ c) 20:39, 24 January 2018 (UTC)
@Eric Kvaalen: I'm just going to ignore your insults here and try to deal with the facts. To be frank, your unsourced talk-page calculations just don't matter because they are considered WP:OR. What if somebody later comes along and changes it, saying the value is wrong? What do we do? That's why we need sources to make this encyclopedia accurate. Likewise, saying vague words like "far" can prove confusing to the lay reader because it is a relative term with no definite meaning. If we're going to get through this, then I'd like to see definitive wording with sourced data. That will help us anchor the information and keep it intact for future use. If citations aren't available, then tough.
To cite something like this, I recommend looking for a reliable source that demonstrates exactly what you are trying to present. You can then use WP:CALC and present your calculation, step by step. That will allow others to check your work at a future date. Thank you. Praemonitus (talk) 21:36, 24 January 2018 (UTC)


@Praemonitus: I did not insult you.

You did not answer my questions. Do you agree that it moves about 70° or not? To quote WP:CALC which you refer to, "Routine calculations do not count as original research, provided there is consensus among editors that the result of the calculation is obvious, correct, and a meaningful reflection of the sources." It's a routine calculation, which I think you are capable of understanding. I will repeat it here:

The system is moving towards us at about 45° (velocity component towards us is 22 km/s, and sideways component is 23 km/s). So in 28,000 years, when it gets to the point nearest the solar system, it will have moved by 45°. At any point in time, one can draw a right triangle going from the sun to the point of nearest approach, from there to the Alpha/Proxima system, and from there back to the sun. (The right angle is at the point of nearest approach.) The line from here to the point of nearest approach is like the cosine (times the hypotenuse), whereas the segment from there to the system is like the sine (times the hypotenuse). The latter changes linearly with time. So the tangent changes linearly with time. In 28,000 years it changes by about 1 (from 1 to 0). So in the next 12,000 years after closent approach it will change by 12,000/28,000, which means the angle will change by arctan(12/28) or 23°. So in all, over the next 40,000 years, the angle will change by 45°+23°=68°. Approximately. The point is, it's a lot! To just say the system will have "moved west" misses the whole point. That could mean it moves west by 1°.

Eric Kvaalen (talk) 06:56, 25 January 2018 (UTC)

The calculations you are presenting are original research. They are not "obvious, correct, and a meaningful reflection of the sources". Among other things, I don't see a source for your velocity vectors as stated. I assume you calculated the lateral motion, rather than finding it in a source. Regardless, the calculations could be done, but they would still not be obvious unless you provide them in better detail than above. You'd have to provide the vector calculations to produce an actual answer, not a handwaving approximation in words.
Even if you did that, you probably wouldn't get consensus on making your change. To re-use the ship analogy, it's like presenting a picture of a ship with a rotating radar dish sketched in, and wanting to add to the caption saying "by the time the dish finishes a rotation, this picture will be inaccurate because the ship will be foreshortened." That's meaningless trivia. Tarl N. (discuss) 09:01, 25 January 2018 (UTC)
In addition, I'll comment that you seem to find a need to publish your thoughts. Wikipedia is not the place for that. If you want to publish your thoughts, write articles for publications, elsewhere. Tarl N. (discuss) 09:03, 25 January 2018 (UTC)
@Praemonitus: "Do you agree that it moves about 70° or not?" My opinion on that doesn't matter because it's OR. Praemonitus (talk) 19:19, 25 January 2018 (UTC)


@Tarl N. and Praemonitus: It's not that the ship will be foreshortened. It's that the ship passes us by, moving by 168°, while the radar dish does one single rotation!

My source for the veloctiy components is the article by Kervella referenced in the Alpha Centauri article, namely this. I calculated the sideways component by the Pythagorean theorem.

I accept that saying that the system will move 70° over the next 40,000 years borders on original research (although it is trivial, and we could easily ask the researchers whether it is correct). But all I wanted to do was to put in the word "far". I thought you would be able to follow the argument for why it will move far. (I think whether you agree is important, Praemonitus, because if you believe that it moves 70° and yet you refuse to let me add the word "far", then I question your motives.) Do you accept that in 28,000 years, by the time it gets to its point of closest approach, it will have moved by 45°? Surely you can understand that. It doesn't involve any arctangent.

Eric Kvaalen (talk) 06:14, 26 January 2018 (UTC)

@Eric Kvaalen: Look, I understand and follow your arguments. However, you are in error by asserting that the vague word "far" describes an angular movement. Until you provide a properly cited statement for your values, there's nothing further to discuss. I am also starting to question your motives in this matter. Praemonitus (talk) 15:58, 26 January 2018 (UTC)
The above comment by Praemonitus was changed on the 27th at 17:20. When I responded it just said "Look, I understand and follow your arguments. But until you provide a properly cited statement, there's nothing further to discuss." Eric Kvaalen (talk) 16:15, 29 January 2018 (UTC)

Tarl N., you seem to agree that if we have consensus that the star system moves far in 40,000 years, then we can put the word "far" back in. Praemonitus acknowledges that he follows my argument. What about you? Do you agree that it moves far in 40,000 years? Eric Kvaalen (talk) 16:45, 27 January 2018 (UTC)

It's vague, irrelevant to the picture, and, uncited. That it moves a considerable distance in 40,000 years isn't in dispute - it has a proper motion, thus it moves. The disagreement you're having with Praemonitus is how to characterize that, plus that you have no citation for your conclusion. The disagreement with me is that it's irrelevant at the point where you want to put it, and that your WP:OR calculations are neither obvious nor trivial - as demonstrated by the fact that you haven't actually carried them out (you've hand-waved approximations). From a maintainability viewpoint, adding such calculations is purely WP:OR. The current note is clumsy, if I made any changes I'd probably re-word it to something like "Note that by the time Proxima completes one orbit, the entire Alpha Centauri system will have moved to another part of the sky, so the perspective and background will be different". Even that, I'd regard largely obvious trivia. Tarl N. (discuss) 17:56, 27 January 2018 (UTC)


Tarl N., the question is not whether it moves "a considerable distance". The question is whether it moves by a large angle. Look, if you don't follow my "hand waving" explanation (not even the fact that it will move 45° in the next 28,000 years?), then just do a simple calculation of how many light-years it will go in the next 40,000 years! It's trivial. It comes to about 4 light-years, and it's moving presently at about 45° away from "vertical". It's presently 4 light-years away. So obviously it will move through a large angle, not just during the present orbit, but just in the next fraction of an orbit (40,000 years out of half a million). But I accept your proposed version of the note (with a slight change), so I will make it. Eric Kvaalen (talk) 16:15, 29 January 2018 (UTC)

It's not that I don't follow your explanation, it's that you hand-wave the hard calculations and get them wrong. You have to do a 3-dimensional vector translation (convert from r/RA/DEC to xyz in km, apply linear translation with xyz velocity in km/s, convert from resulting xyz in km to r/RA/DEC, and calculate angular separation). It's a couple of hours of work to set up for me, which I haven't had time to do. It's non-trivial, as demonstrated by the 6000 words of argument over 19 days, and nobody has done it. It's blatantly WP:OR, particularly since I have not seen a published value for Alpha Centauri's transverse velocity and direction. It's derivable, but each step is one further beyond the "obvious and trivial". The hand-waving calculations are fine for order of magnitude (for example, good enough for removing a claim that it would move 4˚ in the next century), but not sufficient for adding a specific comment on how far it will move in a half-million years. See WP:CITOGEN for examples of why it pays to be anal-retentive on prohibiting WP:OR. Tarl N. (discuss) 22:57, 29 January 2018 (UTC)
From Anderson and Francis (2012), for Proxima Centauri I get a total heliocentric velocity of 32.6 km/s.[2] Ignoring the effects of galactic gravitational potential, over 40,000 years that translates to 4.1151×10+13 km[3], or 41.15/9.46 = 4.3 light years traveled. In astronomical terms, that's not much. Plus the actual value is off-topic WP:TRIVIA that adds no value to the article. Praemonitus (talk) 00:41, 30 January 2018 (UTC)
Well, I can no longer say I've never seen transverse velocity published. The XHIP catalog gives me u,v,w vectors in km/s, with the commentary that these should be safe for linear motion calculations up to 2MYr. But where are you getting 32.6 km/s from, however? I get 31.896 km/s for A and 30.243 km/s for B. That's from U,V,W values of A=(-29.3,0.3,12.6), B=(-26.2,-0.4,15.1). (Retrieved from VizieR specifying Alpha Centauri and clicking the u,v,w selections). Which still leaves the issue of the overall system's motion unresolved - and calculating that from scratch is even less obvious and trivial. Tarl N. (discuss) 02:19, 30 January 2018 (UTC)
I went to the Vizier form and selected the UVW field for HIP 70890. But you're right, I should be using Alf Cen AB since Proxima Cen probably includes an orbital velocity component. Praemonitus (talk) 02:54, 30 January 2018 (UTC)

References

  1. ^ "Orbit of Proxima Centauri Determined After 100 Years - Strongest evidence yet that Proxima Centauri orbits Alpha Centauri pair". www.eso.org. Retrieved December 26, 2016.
  2. ^ Meeus, Jean (2002). More Mathematical Astronomy Morsels. Willman-Bell, Inc. p. 347.
O.k. - I did a rough calculation. See pdf for my rough calculations, using only Alpha's proper motion. This is very rough, since my source numbers are so rough. But I ended up calculating that Alpha Centauri will be in the Pictor constellation near where Canopus is (now) in 40,000 years (obviously neither Canopus nor Pictor will be there at the time). Total motion about 50˚ in 40,000 years. Tarl N. (discuss) 03:49, 30 January 2018 (UTC)
And this is why you don't use WP:OR on Wikipedia. I got a sign wrong. It will be in Hydra, not Pictor. Galactic longitude 257, Galactic Latitude +29˚. Tarl N. (discuss) 03:49, 30 January 2018 (UTC)


Tarl N., it wasn't necessary to do a detailed calculation as you describe. The question was how far (in angle) the system will move in the next 40,000 years. For that all you need is its velocity components toward us and sideways (which you can easily get using the Pythagorean theorem), and its distance now. By the way, since we know that it presently moves about 1° per thousand years, and that the figure will be greater than this over the next 56,000 years because it will be closer to the sun, then obviously it will move more than 40° in the next 40,000 years. And it is moving generally west, along the line of the Milky Way. I did calculate the velocity components of the Alpha/Proxima system. Proxima changes the result very little since it has approximately the same motion relative to us as Alpha and because its mass is much smaller.

But I don't need to convince you of all this since you have finally allowed me to add my note, although Praemonitus shoved it into a footnote where no one will see it.

Eric Kvaalen (talk) 14:32, 30 January 2018 (UTC)

Yeah, I shoved it back in a note where it was before, and as agreed during the discussion above. It's not like there aren't other explanatory comments in the notes section, so spare us your trivial indignities and just use a mouse-over to read it. WP:EGO. Praemonitus (talk) 18:12, 30 January 2018 (UTC)

Dust rings

Dust rings reported in November may not exist 

But when MacGregor, Weinberger, and their team looked at the ALMA data as a function of observing time, instead of averaging it all together, they were able to see the transient explosion of radiation emitted from Proxima Centauri for what it truly was.  "There is now no reason to think that there is a substantial amount of dust around Proxima Cen," Weinberger said. "Nor is there any information yet that indicates the star has a rich planetary system like ours."
Preprint, Accepted to ApJL. Lithopsian (talk) 19:45, 27 February 2018 (UTC)
Thank you. I've updated the article and removed the entries from the planetary system table. Praemonitus (talk) 21:28, 1 March 2018 (UTC)

The giant planet of ~0.31 Jupiter mass should probably be removed from the planetary system table as well. There is clearly no evidence of this planet's existence. -- J P

Given the variable nature of this star, it's probably a good idea to only list confirmed candidates. Praemonitus (talk) 21:36, 13 March 2018 (UTC)

Major image is messed up

HST imagery would not show these streaks of light at 90 degree angles. This imagery has been artifically processed, so its accuracy is questionable. This is NASA promotional imagery, not truly scientific. Also, References to this picture refer to WW2 which has nothing to do with the image either. --2600:6C48:7006:200:D84D:5A80:173:901D (talk) 04:44, 15 March 2018 (UTC)

I can't tell if you're trolling or serious. There could be any number of reasons for the 90 degree angle; most likely it is simply aesthetics because it looks a bit nicer with the rays going toward the corners rather than the edges. Doesn't change the quality or accuracy of the image, and certainly doesn't make it any less scientific. Also, I have no idea what "References to this picture refer to WW2" means, so we're going to conveniently ignore that nonsense. — Huntster (t @ c) 06:27, 15 March 2018 (UTC)
JFTR those “streaks” are just diffraction spikes, nothing to do with digital manipulation.—Odysseus1479 08:13, 15 March 2018 (UTC)
Yes, that. Forgot to say that. Thanks Odysseus. — Huntster (t @ c) 12:07, 15 March 2018 (UTC)
Seriously? OK, I'll assume good faith. What the others said, obviously. Have some fun and look up your favourite objects at the Hubble legacy archive. You will probably be astonished at just how crude raw HST imagery is, if all you're used to is the highly-processed and "artificial" images shown on most space porn websites. They're not colour for a start (deliberately), although the same frames may be available at several wavelengths that can be combined to form a (real- or false-) colour image. They are "noisy", that is covered in spurious specks or streaks in addition to the optically real aberrations such as diffraction spikes. They also tend to show very little detail because of the unbelievable range of brightnesses contained within the raw image, which must be adjusted to a range that is visible to viewers while covering the detail that is considered important in that image (and possibly not showing other important details). Lastly, which surprises many people, is that the image frames tend to be a weird shape and orientation rather than a simple north-is-up (or down if you're old school or living in the less-populated hemisphere) square that you might expect. Occasionally this is visible in a final processed image, but often it is obscured by tilting the image so that north is off at some angle, or cropping it so that north can be up on a nice square palette. Lithopsian (talk) 15:01, 15 March 2018 (UTC)
The Hubble FAQ has an explanation for the spikes.[4] It's well understood scientifically. Praemonitus (talk) 15:51, 15 March 2018 (UTC)

Density calculation

The density is calculated in the "explanatory notes" using 0.145*R_sun, but the stellar radius is listed in the info box as 0.154*R_sun. Since volume is proportional to the cube of radius this results in a significant discrepancy.

Mean density is currently listed in the "characteristics" section as 56.8 g/cm^3 using 0.145*R_sun, but in fact works out closer to 47.0 g/cm^3 using 0.154*R_sun. Lord Parkin (talk) 05:23, 14 March 2018 (UTC)

It's a meaningless value anyway since it's only relevant at one (undefined) interior layer of the star. It might be more useful to discuss surface gravity instead. Praemonitus (talk) 14:27, 14 March 2018 (UTC)
The overall density of a star is a moderately pointless thing to calculate. Possibly the point being made in this article, that it is 40 times denser than the sun, is interesting although I don't know if it has to be in the lead. Looks like a typo in the calculation though. Lithopsian (talk) 17:32, 14 March 2018 (UTC)
I've updated the calculation using the values in the infobox. Praemonitus (talk) 20:22, 16 March 2018 (UTC)

Whole star convection?

In the "Characteristics" section of the article, it is said: "Because of its low mass, the interior of the star is completely convective, causing energy to be transferred to the exterior by the physical movement of plasma rather than through radiative processes." The only source cited for this is [22], but, as far as I can see, it I does't say that the star is "completely convective". It does discuss what amounts to persistent convection over a long time, but, again, as far as I can see, not whole body convection. Attic Salt (talk) 12:58, 20 September 2018 (UTC)

Unfortunately it's implicit: "First, notice that the star remains convective for 5.74 trillion years. As a result, the star has access to almost all of its nuclear fuel for almost all of its lifetime." I'll see if I can dig up a second citation. Praemonitus (talk) 15:59, 20 September 2018 (UTC)

Diameter can be measured directly ????

Article's introduction 2nd paragraph says: "Because of Proxima Centauri's proximity to Earth, its angular diameter can be measured directly." I can find no evidence or cite for this, and it seems it is just calculated from stellar parameters. e.g. inferred. Due to its faintness, stellar interferometry will not work, which is the only direct method available today.

Statement should be removed unless it can be referenced as such. Arianewiki1 (talk) 02:27, 23 September 2018 (UTC)

Ségransan et al. (2003).[5] Citation #12 in the article. Praemonitus (talk) 03:06, 23 September 2018 (UTC)

Proxima c

Something to watch for once it gets published somewhere more substantial than twitter:

https://twitter.com/LeeBillings/status/1116788239396851712

©Geni (talk) 22:54, 12 April 2019 (UTC)

And also of course, the Breakthrough Discuss: Day 2, Session 2 video on facebook (and other sites too): here — Preceding unsigned comment added by 86.162.210.247 (talk) 22:43, 13 April 2019 (UTC)
First of all, since err... Erm.. Our results are still under revision, and so embargoed. We, erm.. please don't, we ask you don't, not to advertise these results outside. Err... So, thank you for the comprehension. — Preceding unsigned comment added by 86.158.124.111 (talk) 07:10, 22 April 2019 (UTC)
It is appropriate to wait until the results are fully verified. False planet findings have happened before. Praemonitus (talk) 15:43, 22 April 2019 (UTC)

WISE Data

Hasn't WISE ruled out any brown dwarfs closer to us than PC?

05:20, 31 August 2019 (UTC) — Preceding unsigned comment added by CrackDragon (talk • contribs)

Do you have a reference? There's an informal reference here, but it's not peer-reviewed. Praemonitus (talk) 12:55, 31 August 2019 (UTC)

Distance

Problems still continue. Distance 4.246ly in the infobox, should correspond to 4.25ly in the article body. And even the parallax 768.13mas in the infobox does not correspond with the citation number 2, page 12, where is 774.25mas. — Preceding unsigned comment added by 167.58.188.232 (talk) 20:52, 29 March 2016 (UTC)

Citation 2 shouldn't have been used for the parallax reference because the data comes from van Leeuwen (2007). These types of issues can happen with open wikis. Praemonitus (talk) 22:39, 29 March 2016 (UTC)
Ok, but citation 1 (van Leeuwen 2007) has no explicit reference to Proxima parallax. — Preceding unsigned comment added by 167.58.78.217 (talk) 06:00, 31 March 2016 (UTC)

One of the pictures has "distance" where it should be "discovered" in 1915 or whatever. Someone who is a serious wikipedian can put this properly. — Preceding unsigned comment added by 82.2.122.59 (talk) 12:28, 30 October 2015 (UTC) The first paragraph states that Proxima Centauri is "about 4.22 light-years distant". Yet the sidebar gives a distance of 4.243ly. There is no reference for either. A professional astronomer should identify a definitive reference and one (or both) of these numbers should be corrected. KevinTernes (talk) 13:21, 8 August 2012 (UTC)

At one point they did match, but somebody took it upon themselves to use an obsolete reference to insert a superseded value. I'm surprised it took this long for somebody to notice, so thanks for bringing it up. In the infobox, the parallax information is cited and that data is used to compute the distance. I've corrected the lead and article body to match, then removed the obtuse kilometre value because for most people it is unhelpful. Regards, RJH (talk) 15:32, 8 August 2012 (UTC)

More on distance. In the Observation section, we see, "In 1917, at the Royal Observatory at the Cape of Good Hope, the Dutch astronomer Joan Voûte measured the star's trigonometric parallax and confirmed that Proxima Centauri was the same distance from the Sun as Alpha Centauri." However, the wiki article gives the distance to Alpha Centauri as 4.37 ly, not 4.24 ly. One cannot "confirm" something that is false. I didn't try to fix it, because I don't know if Voûte made an error, or whether his level of accuracy was maybe one digit, i.e. 4 ly. If it is the latter case, then maybe add the word "approximately", i.e. "was approximately the same distance..."77Mike77 (talk) 17:03, 18 March 2013 (UTC)

It is in such a wide orbit around Alpha Centauri that the distance is noticeably different. --JorisvS (talk) 23:13, 18 March 2013 (UTC)
I see. Perhaps, then, the phrase "at that time" could be added for clarity. I will add that later if there is no objection.77Mike77 (talk) 00:11, 20 March 2013 (UTC)
The only concern I have is that the new phrasing ("It is currently 4.24 ly from the Sun" [italics mine]) might give people the impression that this distance changes on "small" time scales, i.e. within a human lifetime or so (which isn't true). The distance to Proxima is just about as constant as (or rather more constant than (!)) that to other stars (as can be seen in the graph in the article). Saying only here that the distance is "currently" something and not adding the same qualifier to the distances to other stars hence gives an incorrect impression of the situation. --JorisvS (talk) 18:42, 20 March 2013 (UTC)
I put in "currently" because of this other statement. "In 1917, at the Royal Observatory at the Cape of Good Hope, the Dutch astronomer Joan Voûte measured the star's trigonometric parallax and confirmed that Proxima Centauri was the same distance from the Sun as Alpha Centauri." If it was the same distance away as Alpha Centauri (4.37 ly) in 1917, and 4.24 ly away today, then I thought it was appropriate to say "currently 4.24 ly from the Sun". Perhaps the info needs to be reorganized so that these ideas aren't so separated. There is also the idea that Proxima is in a wide orbit around the Alpha binary, with distance from the Sun varying periodically, as you noted above. I'll think some more on this.77Mike77 (talk) 19:34, 20 March 2013 (UTC)

--- The distance DOES vary periodically, on a scale of 10s of thousands of years --- — Preceding unsigned comment added by 2.97.119.194 (talk) 21:27, 15 January 2020 (UTC)

This site http://www.saao.ac.za/~isg/proxima.html says that Voûte was wrong:
"Eighty-two years after the Cape discovery, Robert Innes at the Union Observatory in Johannesburg found a fainter star near alpha Cen that he suspected was a third but somewhat separated member of the same system. Its distance was measured over the following two years by Joan Voûte at the Royal Observatory and by Innes himself, unknown to each other. Innes prematurely declared it to be closer than alpha and named it 'Proxima Centauri', or 'Proxima' for short. Voûte's better-quality observations suggested it was no closer then alpha but, in fact, he was wrong and Innes was right, largely by chance!" So maybe the word "confirmed" needs to be changed. There are numerous sites that have copied the wikipedia article, and not much else.77Mike77 (talk) 20:10, 20 March 2013 (UTC)
I don't know about the history, you could be right about the "confirmed", but I don't really care what you do with it. What the "same distance" is supposed to mean is that the difference in the distances in so small that the stars are associated with each other (as opposed to very different distances). --JorisvS (talk) 20:42, 20 March 2013 (UTC)
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