Talk:Alpha Centauri

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[edit] Hello wonderful writers!

There is one page, the Alpha Centauri page, that is regarding the star system as a whole (general info about all three stars: Alpha Centauri A and B, and Proxima Centauri). The page links to separate detail pages for each of the three stars. The one detail page about Alpha Centauri A indicates a Solar Luminance of 1.519. The main Alpha Centauri star-system page, however, indicates 1.57. Do you know which is the correct Luminance for Alpha Centauri A?

Answer: 1.519 is the best figure, see http://www.eso.org/outreach/press-rel/pr-2003/pr-05-03.html

Thanks. Once again, these pages are great!

Tesseract 501@aol.com

[edit] 'A' out of focus

'A' component in the picture titled "Apparent and real trajectory of B component relative to A component" does not lie on bigger axis of B's orbit. More precicely, "flat" orbit is ok, but "tilted" orbit, as we supposedly are seeing it from Earth, is not. Either there is a mistake, or "tilted" pic accounts for the fact that A is not stationary, but has much smaller elliptic orbit too. If it's true, then "flat" orbit needs fixing instead.

On the image A is 'stationary' - B's trajectory is relative to the static A. A being out of the apparent B's trajectory focus is correct.
The assumption that the 'tilted' (yes, still apparently elliptical) orbit of B should have A in it's focus is NOT correct.
An orthonormal transformation (simply: rotation) of the 'flat' elliptical orbit in 3D again produces ellipse, however it is NOT invariant to the focus: focus of the source ellipse is NOT transformed to focus of the destination ellipse.
A nice example is that for some rotations ellipse transforms to apparent circle, but its originally 2 focuses do not turn to the single circle center. It could happen only for the singular case when ellipse transforms to apparent abscissa (but even in this case focus can transform to variety of positions)
Please, also consider the axes and peaks of the 'flat' ellipse are NOT transformed to axes and peaks of the "tilted" ellipse.
Finally the shortest/longest year segment in the apparent orbit does not match with the shortest/longest year segment on the real orbit (you can check it easily).
Though it seems like the well known Kepler's laws do not work on the image, you should take into account that the laws do NOT describe how it should appear to an observer - in plane perpendicular to his view direction. The laws are related to the plane in which the objects are really orbiting.
--Eltwarg 14:36, 5 August 2007 (UTC)

[edit] Inclination (to plane of "sky")

Howdy, There is reference under the FACTS section of the Alpha Centauri page (for the star system): Inclination (to plane of sky): 79.24º When the word "sky" is used, does it mean Inclination to the Earth's Ecliptic, or the Inclination to the Primary Star's plane of orbit? I rather doubt that the reference relates to the Galatic Plane? To quote another part of Wikipedia, it might mean, "The ... angle between the normal to the orbital plane and the direction to the observer, since no other reference is available. Binary stars with inclination close to 90 degrees (edge-on) are often eclipsing." If that is the case, doesn't the angle change if it is based on an observer in the Northern Hemisphere, versus on the Equator, versus in the Southern Hemisphere? Thanks, Your easily confused fan, Tesseract 501@aol.com (August 20, 2005)

The definition you quote is the correct one. And, no, it does not depend on where you observe from. It may help to visualise the sky like the ancients did: as a huge spherical backdrop surrounding Earth. It is far enough that rays from observers looking at the same point from various locations on Earth will hit the spherical walls at the same angle: head-on.
Urhixidur 15:57, 1 October 2005 (UTC)

[edit] Sky appearance

A bit of a request here - would it be possible to know what the sky would look like on a planet orbiting either one of the stars? It would be fascinating to know how the sunrises and sunsets would look, how long night would be given the two suns in the sky, that sort of thing. Assuming an orbit within the habitable zone, somewhere within 0.8 to 3 AU or so depending on which star it is. Mithridates 07:46, 1 October 2005 (UTC)

Thanks! That's exactly the description I was hoping for. ^^ Mithridates 08:27, 21 October 2005 (UTC)

Assuming a planet has an orbit in the same plane as the two stars orbit each other (which is most likely), at one point in the planet's year, the two stars would rise and set together, and in fact, the star the planet orbits would appear to occult the other star. Exactly half a year later, the stars would be directly opposite to each other, and, if the planet has no axial tilt, one would be rising as the other is setting. (If there is an axial tilt, there may be periods of twilight or darkness since one star will be in the sky for less than half a day, or an overlap with both stars above the horizon.) In the intervening months, the secondary star rises and sets earlier each day relative to the primary star. This phenomenon occurs regardless of which star the planet orbits.

However, a planet that orbits both stars, at such a considerable distance that it would be colder than Pluto, would see the two stars together at all times, though varying in their positions as they revolve about each other, with the planet taking so many thousands of years to revolve that the stars' movements are much faster. GBC 19:03, 2 February 2006 (UTC)

[edit] Names

Here it says Rigil Centaurus=Toliman=Alpha Centauri; but http://en.wikipedia.org/wiki/Alpha_Centauri_A says Alpha Centauri *A*=Rigil Centaurus=Toliman. Also http://en.wikipedia.org/wiki/List_of_nearest_stars says Alpha Centauri *A*=Rigil Centaurus=Toliman. In my opinion, since Bayer gave the name "Alpha Centauri" to the star known as "Rigil Centaurus" or "Toliman", then Alpha Centauri=Rigil Centaurus=Toliman. Also, the "Facts" section gives apparent and absolute magnitudes, but fails to mention that these are the magnitudes of Alpha Centauri A, not the magnitudes of the entire Alpha Centauri system.

[edit] Distance

The article states in the System Components section that the distance of the binary system of Alpha Centauri A and Alpha Centauri B is 4.36 light years, while the distance to the Alpha Centauri C or Proxima Centauri is 4.22 light years. However, in the Facts section, the distance to Alpha Centauri is given as 4.396 light years. I suspect that the number given in the Facts section is incorrect or was miswritten to include an extra "9". Anchr 14:53, 13 November 2005 (UTC)

4.396 (actually 4.394 using more accurate conversions) probably comes from the Hipparcos parallax of 742.24 mas. I don't know where the value that is used in the article came from. Ardric47 22:28, 19 March 2006 (UTC)
Some of the distances may be from older sources. Alpha Centauri has been "receding" from us as astronomers refine their parallax equipment. In the 1893 World Almanac, it was reported as 3.26 light years from Earth (20 trillion miles, or 20 x 10 to the 12th power), equal to one second of parallax. By the 1960s, the distance was refined to 4.2 light years, and through the 1970s and 1980s, 4.3 light years. I learned of 4.393 (25.8 x 10 to the 12th power) light years from the website of the South African Astronomical Observatory, sometime around 2000. GBC 16:28, 8 September 2006 (UTC)

[edit] Total visual magnitude

"and contains the fourth brightest star in the sky, with a total visual magnitude of −0.01."

is the total really necessary, since, for all intents and purposes, Alpha Centauri A is effectively a point source of light as seen from Earth (well under 10 milliarcseconds) - we're not really integrating over a large surface. Richard B 03:22, 18 November 2005 (UTC)

[edit] Planets + question

Anyway we can source our claims in the potential planet section? [Here] is a primary source used at Planetary habitability which may be of some use.

Also, I'm a little confused myself about "contains" the fourth brightest star. How, for an Earth observer, is the apparent visual magnitude of A seperable from its companions?

With a telescope (or binoculars), the 2 primary stars of Alpha Cen are resolvable into distinct components, and will appear as bright as their individual app. magnitude dictate. To the naked eye, they are too close for most people to be able to split them as distinct stars, so appear as a single, brighter star Richard B 18:48, 2 February 2006 (UTC)

Hello... I just found a blog entry with some new information about the possibility of planets around Alpha Centauri. The link is [here]. I'd edit the entry myself, but I'm not quite sure how to do citations and notes, so I'll leave it to more experienced hands. -- CLB

[edit] Merger w/ Proxima Centauri

There are two reason behind the proposal.

  1. They logically belong together. This article already mentions Proxima a number of times.
  2. Readers looking at one article will inevitably look at the other anyway. We might as well save them the trouble.

B00P 05:53, 14 February 2006 (UTC)

I oppose the proposed merger - the two stars are each notable in their own right and merit separate articles, though they should of course refer to each other. I think it's not inevitable at all that people looking for info on one of them would be looking for info on the other as well. Worldtraveller 00:53, 17 February 2006 (UTC)

Notable, undoubtedly, but that doesn't mean that they need two articles. Sirius B is notable, but it's on the same page as Sirius A. The same is true for Alcor, which is located on the page for Mizar.

Additionally, if α Cen C deserves its own article, why do α Cen A and B not deserve one each?

In all other cases it is star systems that get the article. It makes sense to treat this case no differently from the others.

Perhaps "inevitable" was slightly overstating it; I'll stand by "likely." B00P 07:12, 17 February 2006 (UTC)

Proxima may not even be orbititing Alpha A & B, and they are separately important: Proxima is the closest star to Sol, and Alpha A & B are the closest large / stable stars. I also oppose the merge. (I also changed the title of this section: the page being merged is Proxima Centauri, and the "Alpha Centauri C" name is not universally accepted.) DenisMoskowitz 18:34, 21 February 2006 (UTC)
  • oppose proxima centauri is a very notable star, that everyone would search and it would odd if that would lead to this article, it would seem a mistake in a first glance. That occured to me once. I'm not a star fan, but i wanted to know more about Proxima Centari, for my surprise it leded to this article, I'm not sure if it was in the English wiki or in another wikipedia. --Pedro 21:40, 21 February 2006 (UTC)
Oppose. Of course Proxima Centauri deserves own article.--Jyril 17:45, 1 March 2006 (UTC)

Oppose. It should have its's own article. Fosnez 13:41, 8 March 2006 (UTC)

  • Oppose. They are seperate stars, so articles should be seperate. --GW_Simulations 13:23, 12 March 2006 (UTC)
  • Oppose. Proxima Centauri is a unique astronomical object and therefore deserves its own unique Wikipedia entry. --SirCyan Sun Mar 12 20:57:56 PST 2006
  • Oppose. I'm flabberghasted it's even come to this. Barryvalder 09:15, 21 March 2006 (UTC)
  • Oppose. the age of the star system is not the same —Preceding unsigned comment added by Korbindallis (talk • contribs) 00:52, 23 March 2006

More than a month later, few are in favor. I'm removing the tags. —Preceding unsigned comment added by DenisMoskowitz (talk • contribs) 19:59, 24 March 2006

[edit] Error in the data?

The value of the inclination in degrees is the same as the orbital period in years. Could this be an error? The probability for an random coincidence of all four significant digits is about 10-4. From Internet Stellar Data Base I get 79.92 year but no information about the inclination. Where are the values in the article taken from?--SiriusB 16:48, 7 March 2006 (UTC)

It wouldn't hurt to have references, so the values could be checked.--Jyril 20:21, 8 March 2006 (UTC)
References are very much necessary; see my comment above about the distance. Ardric47 22:29, 19 March 2006 (UTC)

Ah - I don't agree that Adam Strange was envisioned quite that way. The stories have him battling alien forces and saving the inhabitants of Rann -- PFS 10 June 2006 (UTC)

[edit] Pointless move

The name of Alpha Centauri system is Alpha Centauri (consisting of the stars Alpha Centauri A, Alpha Centauri B and Proxima Centauri).--JyriL talk 08:03, 14 July 2006 (UTC)

I agree and recommend that it be moved back. Otherwise, to be consistent, all multiple star pages should be moved. These include Capella, Acrux, Alnitak, Gamma Velorum, Dubhe, Castor, Delta Velorum, Alpha Coronae Borealis, Almach, Mizar, Gamma Leonis, Epsilon Carinae, and many more. --Fournax 12:19, 14 July 2006 (UTC)
Those pages actually discuss a star rather than a star system, whereas this article does not start off mentioning any particular star. "Alpha Centauri" is a star, the "Alpha Centauri system" is where it's located. Helicoptor 13:03, 14 July 2006 (UTC)
No, those pages discuss star systems. For example, the second sentence of the Capella article: "Although it appears as a single point to the naked eye, Capella is actually a bright close binary pair of stars along side a second, fainter binary." Alpha Centauri looks to the human eye like a bright point of light in the sky. But it's really a star system containing three stars: Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. There is no massive, compact body of plasma in outer space that is currently producing energy through nuclear fusion called "Alpha Centauri." --Fournax 13:40, 14 July 2006 (UTC)

I've added the page to Wikipedia:Requested moves. --Fournax 22:13, 16 July 2006 (UTC)

Strongly support move back to Alpha Centauri, and in any case Centauri should be capitalised. Chaos syndrome 13:13, 22 July 2006 (UTC)

This article has been renamed as the result of a move request. Vegaswikian 05:32, 26 July 2006 (UTC)

[edit] Sky appearance from the Alpha Centauri system

There are so many unverified claims in this section. Helicoptor 13:05, 14 July 2006 (UTC)

I've added an image to clarify somewhat where our Sun would appear in the sky from Alpha Centauri. The write-up is pretty accurate, but I don't have any further references. RandyKaelber 03:24, 13 October 2006 (UTC)

[edit] When is a Cen A closer than a Cen B?

With an inclination of about 80 degrees, this means from a potential planet around one star the other star would outshine our Sun for parts of the year. Is there a method that this could be found out from the system data on the side bar?

Not sure what you mean - a planet around either would probably be in the same orbital plane as the two suns, so the other would appear kind of like a bright Saturn from the planet. Our sun would be a star in their sky, much smaller than either A or B. DenisMoskowitz 15:00, 8 September 2006 (UTC)

I was thinking about how it is the scattered light from the Sun that makes it hard to see anything else on the sky by day except Luna. It is very hard to find Venus even at its brightest (-4.6m) and most elongated from the Sun (about 45 degrees) even on a clear day unless one knows exactly where to look.

Now I was thinking that while the secondary star might appear small on the sky of a planet, if it is 6m dimmer than the primary, the scattered light would also be 6m dimmer compared to that of daylight. Also, the Sun would be a 0.5m star on the sky of a planet, therefore about 5m dimmer than Venus is from Earth at its brightest. Depending on which star would be the secondary and where in the orbit both stars are, the secondary would be between 4.6m dimmer (a Cen A from an a Cen B planet at periastron) and 8.6m dimmer (a Cen B from an a Cen A planet at apastron) so I thought the Sun might be very hard to find on the sky when the secondary is at a relatively small angle to it seen from the planet.Ambi Valent 21:15, 21 September 2006 (UTC)

I wonder what "node at 205°" is supposed to mean. Is that 205° from periastron? And would it mean after that point a Cen B is closer than a Cen A? If so, I guess it would mean the direction towards Earth, seen on the flat orbit from a Cen A, would be at 295° from periastron, or about 6 years before each periastron.Ambi Valent 13:15, 22 September 2006 (UTC)

Not sure what the heading is supposed to mean. Closer to what - a planet or Earth? Roughly every 40 years, one of the stars gets closer to us than the other. Planets in the Alpha Centauri system must orbit one of three gravity centers: Alpha Centauri A, Alpha Centauri B, or so far out that it orbits both as if they were one. From the perspective of a planet orbiting one of the two stars, the other would act with the characteristics of Uranus in our solar system - taking some 80 years to return to its original position. However, the planet would experience, in a period slightly over one tropical year, a shift of the non-primary star all around the clock - conjunction at one point, and opposition a half year after that; a quarter year after conjunction, the secondary star would be rising approximately one quarter of a day earlier than the primary star. At all times, both stars would be far, far brighter than Earth's sun. GBC 19:42, 22 September 2006 (UTC)

I meant closer to Earth. Sorry for being unclear. I think I'll make a new question which will help me answer this and other questions.

[edit] Taking the picture of the flat orbit, which star is in x, y or z direction?

On the picture, A is stationary, +x would be the direction where B is at periastron, +y where B moves toward at periastron, and +z the direction towards a viewer for whom the orbit would look flat and counterclockwise like in the picture.Ambi Valent 22:20, 22 September 2006 (UTC)

[edit] About planets

I'm not astronomer, but I have much questions about possibility of habitable planets in Alfa Centauri system. Any planet in this system must have very unstable orbit because gravitional disturbance from another star. Moreover if this planet exist it must have highly unstable conditions on its surface because different quantities of energy which planet obtain when planet is situated between stars and when planet is situated beyond one of stars. From these reasons I believe that none habitable planets are possible in Alfa Centauri system and other double-star systems. Please correct me if I'm wrong.

Actually, the energy a planet in the habitable zone receives from the other star is always minimal; when the stars are closest to each other and the planet is between the stars, it only receives about 1% of its energy from the other star. A planet for which this would be significantly different would have to be more distant from its primary star, and then its orbit would become so unstable that the other star would eventually pull it out of the orbit around its primary to a more chaotic path, probably slingshooting it out of the system entirely. And about stable orbits: Earth's orbit around the Sun is varying over the millenia between round and elliptic (from the small but persistent effects of other planets gravity, mainly Jupiter's), and Luna's orbit around the Earth even more so (from solar gravity effects), but still both have absolute limits which they don't leave, and neither would an Alpha Centauri planet. The only question is exactly how strong the effect would be.Ambi Valent 00:10, 22 October 2006 (UTC)
Is it possible to calculate the maximum distance that planets could potentially form around a star in a binary system without being disrupted by the other star? It would be interesting to note the "planet zone" as well as the "habitable zone". ⇔ ChristTrekker 16:57, 13 December 2006 (UTC)
An article in Astronomy magazine in 1982 said that for the Alpha Centauri system, the maximum distance would be 2.5 AUs from each of the two stars. Beyond that, the gravity of that star would not be dominant enough to overcome periodic tugs from the companion star. I do not know, however, the minimum distance for planets that orbited both stars as a single gravity center. 2.5 AUs is enough to include the inner solar system of our own star, so in theory, both A and B could have four planets, for a total of eight inner planets. The next question is, do those planets exist, and are two, or even one, of them at the right distance from its star for a suitable temperature to allow conditions for life, if that planet has the right chemical elements. Finally, are the planets safe or are they subject to meteor and comet bombardment due to the lack of a Jupiter in close proximity to sweep up those objects? It has been over 10 years since exo-planets began to be found, and I have not heard if anyone's been studying the Alpha Centauri system in search of planets that could be found by those methods already used to discover so many planets around stars that are so many times further away from us. GBC 17:47, 14 December 2006 (UTC)
I've looked at it again, this time how much of a temperature rise it would cause: For a planet of a Cen B, temperature at periastron would be about 2K (nearly 4F) higher than at apastron. This temperature rise starts very slowly, and only the 6 years before and the 6 years after periastron would be 1K or more warmer than at apastron. This would still mean a strong global warming and following cooling every 80 years (comparison: in ice ages temperatures are just 5K lower than between them). For a planet around a Cen A, the effects are 3 times weaker as a Cen B is three times fainter as a Cen A.Ambi Valent 15:55, 22 October 2006 (UTC)
I don't understand how it is possible. Distantion between Cen A and Cen B is only 11.2 astronomical unit, i.e. only slightly more then distantion between Sun and Saturn (9.5 astronomical unit). Both Cen A and Cen B have mass rougly equal to Sun's mass and highly ecliptical orbit (e=0.52). I don't understand how it is possible that temperature on surface of planet is varied in such small limits in these conditions. Dmitry Krotko.
I think the main mistake you're making is either forgetting that 11.2 AU is the minimum, not the average distance, or that you get just 1 percent of the energy at 10 AU that you would get at 1 AU. Let's look at the example of the planet around a Cen B again. Assuming it is earthlike, it has an average temperature of about 288 K (15°Celsius or 59°Fahrenheit). 11.2 AU is the *minimum* distance between the two stars. Since an earthlike planet has an orbital distance about about 0.7 AU (a Cen B being fainter than our Sun, with about half the energy output), the minimum distance between planet and a Cen A is about 10.5 AU. This again means it is about 10.5*10.5 = about 110 times fainter than it would be at 1 AU distance, at which it would have about 1.52 times the energy output of our Sun... so the energy that reaches the planet is 1.52/110 or about 1.4 percent of the energy of our Sun. Add the 100 percent from a Cen B you get 101.4 percent of the energy of our Sun. Temperature is proportional to the square root of the square root of energy, so you get 100.35 percent of the temperature... the 100 percent would be the 288 K, and the 0.35 percent would be 0.0035 * 288 or about 1 K... so the global average temperature then would be 16°C/61°F instead of 15°C/59°F. I'm sorry that my first guesses were way too generous.Ambi Valent 19:22, 23 October 2006 (UTC)
Thanks, that's very interesting. Amazing to think you could have a second star sitting in your backyard and yet it would have very little impact. It gives you a sense of how truly vast astronomical distances are. ⇔ ChristTrekker 16:57, 13 December 2006 (UTC)

[edit] Beta Centauri (Hadar)

Beta Centauri, according to the World Almanac, is 490 light years from Earth's sun. That is 111.36 times as much as Alpha Centauri, which is a shade under 4.4 light years. It may be that the person who deleted the info was confusing Beta Centauri with Alpha Centauri B, the latter being one of the two components of Alpha Centauri. GBC 20:49, 18 December 2006 (UTC)

The third sentence in the first paragraph is kind of confusing. I mistakenly changed it to read "Alpha Centauri A & B" until I realzed that it was referring to the the fact that Alpha Centauri and Beta Centauri, two separate stellar systems, form a visual binary. If this sentence is not essential, I suggest it be removed to avoid confusion. gar in Oakland 03:17, 7 February 2007 (UTC)

[edit] Apparent movement

40 billion years? I bet there's something wrong... I don't think either the Earth, Alpha Centauri, or Beta Centauri will still exist by then. Is 40 million years actually meant? --Army1987 22:29, 21 January 2007 (UTC)

I don't know. It was "40000000000", I changed it for "40 billion". Anyway I don't think we will still be there in either 40 billion or 40 million years. Dravick 03:32, 22 January 2007 (UTC)
Our sun is projected to last another 5 billion years. 40 million years isn't that long in astronomical terms.
And are we talking American or British "billion" here? thx1138 03:02, 30 May 2007 (UTC)
American. I think "billion" always means 1,000,000,000 these days, even in Britain. It certainly does in Australia, where we use British rather than American English. Timb66 23:50, 30 May 2007 (UTC)
The point is moot as 40000000000 was a vandalism replacing 4000 that has since been reverted. -- Paddu 18:37, 16 June 2007 (UTC)

[edit] 100 dots on the trajectory image

The image with the apparent and flat trajectories of B around A seems to have 100 dots along the orbit. This may work fine to show B's higher velocity when in periastron, but the dots do not correspond to years as it appears on the image, since the space between a dot and the next would correspond to the movement in about 0.8 years. —The preceding unsigned comment was added by Ambi Valent (talk • contribs) 22:44, 18 March 2007 (UTC).

You are absolutely right - one dot is exactly 0.8 years on the published image, though there are numbers 2005, 2006, 2007 and 2008... There should have been just 79 dots - 1 dot ~ 1 year - starting on 2005 (the first dot).
It should have worked fine to
- show the changing velocity
- show the calculated position in years 2005-2083
I have not noticed this mistake - thanks for pointing it out!
I will work on fixing it.
--Eltwarg 14:34, 5 August 2007 (UTC)

[edit] Closest Pair

Wikipedia says:

  • "Acrux is a trinary star located 320 light years from the solar system."
  • "Beta Crucis is located approximately 353 light years from Earth's Solar System."
  • "Alpha Centauri is the closest star system to our own solar system at 4.37 light-years."

The second paragraph of this article says, "Alpha and Beta Centauri are the second closest pair of first magnitude stars as seen from the Earth, and due to the effects of proper motion, they will become the closest pair around 2166, overtaking Acrux and Becrux."

Given the three statements this sentence is incomprehensible. Right now α and β Centauri are closer than Acrux and Bcrux and no motion is going to chang that in 159 years.

Could someone please explain what this sentence means? Thanks. Nwbeeson 15:12, 10 April 2007 (UTC)

Quite right. I've actually removed that statement pending clarification from whoever wrote it. What I think that person actually meant was that they were second closest in terms of angular separation. However, it very definitely came across as a blatantly incinsistent statement. 81.154.96.159 20:42, 10 April 2007 (UTC)

It has been put back in again so I have removed it. I assume it is meant to be angular separation, but the assertion is not sourced and in any case is not particularly notable. Timb66 11:51, 16 May 2007 (UTC)

This discussion was in the wrong place (top of the page whereas recent discussions must be at the bottom) which is why I couldn't find it.
Proper motion is the apparent motion of astronomical objects as seen from Earth. So it is obvious that what is meant is the angular separation of these stars as seen from Earth. May be someone can reword "closest pair ... as seen from the Earth" into something more clear.
IMHO that they will become the closest pair of first-magnitude star in another 159 years is as notable as their becoming an optical binary in another 4000 years as both give an idea of the magnitude of the proper motion, and I feel "two very close bright stars" is a feature of the night sky that even a layman can appreciate, and is hence a notable feature. Both these statements are unsourced so we should be searching for their sources (may be one of the external links...). -- Paddu 22:21, 17 May 2007 (UTC)
The text removed in [1] used to clarify that what is being talked about is angular distance. -- Paddu 13:44, 19 May 2007 (UTC)

[edit] Angular distance

Hi. The following sentence is unclear to me: "Seen from Earth, Proxima Centauri is separated by 2 degrees from Alpha Centauri A and B (about 4 times the angular diameter of the full Moon) ..." If they are so close that the human eye cannot distinguish them, how can they be as distant as 4 moons seen from earth? I can easily see lots of details on moon surface even!! -- Dwerk

A and B are a close pair, and C is a much more distant third component. Most (all?) triple systems are like this -- they are called hierarchical triples. Note that A (a G dwarf) and B (a K dwarf) are both bright enough to be seen with the naked eye, but C (an M dwarf) needs a decent telescope. Timb66 12:54, 29 April 2007 (UTC)

[edit] Sid Meier

Doe anyone else think some information on all the things Sid has named Alpha Centrauri should be included, maybe in a Trivia Section, or Other Information? I do. The space ships you build in I think all Civilization games is named Alpha Centraui I. Even a game he made, I'm quite sure, was called Alpha Centauri.—Preceding unsigned comment added by 71.192.223.240 (talk • contribs)

You are correct about the game, but in Civ you are simply sending the ship there. I don't think we need this here. See Stars and planetary systems in fiction and Alpha Centauri in fiction. Michaelbusch 22:30, 25 September 2007 (UTC)
Ah-ha. You are correct..my bad.P—Preceding unsigned comment added by 71.192.223.240 (talk • contribs)

[edit] new stars, change article

They have discovered 17 stars closer too the sun, and one hypothetical one, nemesis, most due to difficulties such as not giving of enough light, were hard to see, 3 of these confirmed stars are classified, and are the USAs worst kept secret, considering any blithering idiot with an alternative light telescope (infra-red, x-ray, microwave, or uv, for instance) can and will notice them. —Preceding unsigned comment added by Avianmosquito (talk • contribs) 02:43, 11 October 2007 (UTC)

I should add that 16 these stars appear to be part of a cluster the sun is in, and are all less then 1/2 of a lightyear from eachother. —Preceding unsigned comment added by Avianmosquito (talk • contribs) 02:49, 11 October 2007 (UTC)

Sounds suspicious to me. Can you provide a link to this "news". Astronaut 10:41, 21 October 2007 (UTC)

[edit] Alpha Centauri closest to Sol in 28,000 years?

I read in A. Ahad's science fiction series - the First Ark to Alpha Centauri [2] - that because of radial velocity and tangential velocity, Alpha Centauri system will be closest to earth in about 28,000 years from today. So this will be a favorable timescale to any earth civilization to cross over in a giant ark vehicle of a journey of 30 to 50,000 years. What is the actual calculation, informed readers here? I think the proper motion is resolvable into tangential and radial velocity components, but I dunno the methods. Pomona17 (talk) 21:56, 18 December 2007 (UTC)

I have added the closest approach and some additional general information on this.

The reference for this is an article is by Robert A.J. Matthews in the now defunct Quarterly Journal of the R.A.S. (QJRAS), 35, 1-9 (1994) entitled "The Close Approach of Stars in the Solar Neighbourhood." This has all the calculation, and information on the Alpha Centauri System. Figure 2 shows the closest star between 1 AD and 50,000 AD. Fairly simple article to read too. However the accuracy is limited mainly on the radial velocity measurements, which is less precise than the proper motions. Still the predictions are about a year or so per millennium and is good enough for the 2000 to 3000 years, but significantly larger beyond about 5000 to 6000 years either side of the present day. Hope this helps.

Adding the reference above after this entry!!!! Arianewiki1 (talk) 01:22, 27 May 2008 (UTC)

V. interesting! I like this reference. I also like the analytics of impact on our Oort cloud. However, it seems rather a shame that Mr. Matthews did not speculate on Alpha Centauri having its own system of Oort cloud (which it now seems could well have one). The story of Mr. Ahad's First Ark links the two systems using a bridge of Oort comets that seems a reasonable concept given our recent observation of other stars with vast shells of encircling material (e.g. Vega, Beta Pictoris, Tau Ceti, Fomalhaut, etc.) Pomona17 (talk) 15:00, 8 June 2008 (UTC)

[edit] Again Sky Appearance

Hello, we have tranlsated some portions of your great english article about that star into german de:Alpha Centauri, in that special case de:Alpha Centauri#Der Himmel über Alpha Centauri. Now we are looking for the main contributor of the chapter "sky appearance". The issue is: it would be nice to have some reference for that text or in other words a source of it. best regards, --FrancescoA (talk) 21:22, 24 February 2008 (UTC)

I have added additional information for you. Much of the general calculations near today are obtained using some simple formulae, mainly using mutual proper motions, radial velocities, and precession, then these are added to a certain date. Longer periods require understanding of the changes in these motions overtime. I.e. The radial velocity decrease on approach, stops, increase as it moves away. Pieces of this appears scattered in many of the professional literature - particularly of the system. None definitive. Matthews' reference in the previous post is probably useful. Note: Some can be simulated in planetarium software - though some have precision issues into the distant past or future.

Arianewiki1 (talk) 01:36, 27 May 2008 (UTC)

Hello Arianewiki1, many thanks for your answer. --FrancescoA (talk) 07:05, 27 May 2008 (UTC)

[edit] Misleading appearance

Although it appears as a single point to the naked eye, Alpha Centauri is actually a system of three stars...

This is misleading. It implies that Proxima Centauri is visually a part of the brighter pair of stars. This is not the case. Proxima is actually more than two degrees away from the brighter pair. -- B.D.Mills  (T, C) 03:20, 16 May 2008 (UTC)

Proxima, although 2 degrees away has a very similar proper motion and parallax, and is very likely attached to the main binary. So this misleading appearance in the quote is actually correct, though a few doubt this based only on the lack of evidence. Ie. Proxima could just share the same proper motions, but is moving independently in its own motion through space.

Arianewiki1 (talk) 01:27, 27 May 2008 (UTC)