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View Full Version : What Exactly is the Nearest Star to Earth?



Knowledge_Seeker
2007-Aug-29, 02:47 AM
Excluding the Sun, I often come upon the sentence, "...Alpha Centauri is the nearest star to Earth," in a few books, a textbook, and today I heard this sentence being said on the "Universe" series.

I have always thought Proxima Centauri was the nearest and sites such as APOD (http://apod.nasa.gov/apod/ap960526.html) and lists like this one (http://cassfos02.ucsd.edu/public/nearest.html) have confirmed what I know. What I heard on the Universe, today is now confusing me, any comments?

OmahaWx
2007-Aug-29, 02:57 AM
I see that Proxima Centauri is 4.2ly and Alpha Centauri is 4.3ly, Yep Im seeing on almost all websites its proxima centauri, sometimes called alpha centauri C.

But yes, I recently took astronomy and I beleive we were taught that alpha centauri was closest. Im not sure, could be that they recently calculated it differently and the textbooks are outdated, who knows...

Knowledge_Seeker
2007-Aug-29, 03:01 AM
Well, I already know that the Alpha Centauri Star system contains Alpha Centauri A, B, and C (with Proxima Centauri as C), but each of those stars has their own names, including Proxima Centauri. So why not just call each star by their name?

01101001
2007-Aug-29, 03:03 AM
Maybe the wording is funny because Alpha Centauri is a system. A (probable) member of the Alpha Centauri system, Proxima Centauri, is currently the closest star to the Sun.

Wikipedia: Alpha Centauri (http://en.wikipedia.org/wiki/Alpha_Centauri)


Alpha Centauri (α Cen / α Centauri, also known as Rigil Kentaurus), is the brightest star system in the southern constellation of Centaurus. Although it appears as a single point to the naked eye, Alpha Centauri is actually a system of three stars [...]
Proxima Centauri, usually regarded as part of the system, is the closest star at 4.22 light-years distant.

OmahaWx
2007-Aug-29, 03:05 AM
Maybe because Alpha Centauri is a system. A (probable) member of the Alpha Centauri system, Proxima Centauri, is currently the closest star to the Sun.

Wikipedia: Alpha Centauri

Brilliant nice find!

most refer to it was the a star that is a little known fact that it is a complex.

thanks for that

Knowledge_Seeker
2007-Aug-29, 03:09 AM
01101001, thanks for pointing that out, but as I mentioned before, why not just call each star by their own name instead of mentioning the system as a whole. I think that calling the nearest star Alpha Centauri C or (perferably) Proxima Centauri is a better way to mention the Sun's nearest companion. That is what irritates me, I wanted to know how others feel.

01101001
2007-Aug-29, 04:40 AM
[...] why not just call each star by their own name instead of mentioning the system as a whole. I think that calling the nearest star Alpha Centauri C or (perferably) Proxima Centauri is a better way to mention the Sun's nearest companion. That is what irritates me, I wanted to know how others feel.

Certainly. It's not very sensible to speak of a 3-member star system as the closest star. That's like asking: which team is the largest football player?

I don't understand why people seem to be speaking that way. Maybe it's just a holdover from the days before we knew Alpha Centauri was a system. It can sometimes take a long time to turn the boat around.

Doing some web searching, I came across such as:
"but since [Proxima Centauri] is part of Alpha, surely it is still fair to call Alpha the closest star". I guess there are people who think of a system as a star.

Well, it's not rare. UCO (University of California Observatories) Lick (Observatory) Ask an Astronomer (http://www.ucolick.org/~mountain/AAA/answers/space/sp3.html) (probably a grad student):
The star Alpha Centauri is about 4 light-years away, so light from Alpha Centauri takes 4 years to get to the Earth.

Urbane Guerrilla
2007-Aug-29, 04:42 AM
At that range, a parsec plus, direct parellax measurements are definitive beyond a doubt.

Knowledge_Seeker
2007-Aug-29, 05:12 AM
Certainly. It's not very sensible to speak of a 3-member star system as the closest star. That's like asking: which team is the largest football player?

I don't understand why people seem to be speaking that way. Maybe it's just a holdover from the days before we knew Alpha Centauri was a system. It can sometimes take a long time to turn the boat around.

I completely agree, I also think people and the media (books and tv shows) should try to promote Proxima Centauri as the closest star.

Saluki
2007-Aug-29, 01:54 PM
The problem is that it is a system, not individual stars. Systems of stars orbit each other. Right now, proxima is the closest, but only because it is at a point in its orbit that makes it closer. This will not always be the case.

It is sort of like the issue we had when Pluto was considered a planet. If you asked "what is the farthest planet from the Sun?", the answer depended on where Pluto was in its orbit.

mfumbesi
2007-Aug-29, 02:17 PM
.......Systems of stars orbit each other. Right now, proxima is the closest, but only because it is at a point in its orbit that makes it closer. This will not always be the case...............


Thank you for say that, I was thinking the same thing, but I didn't have the guts to say it.

01101001
2007-Aug-29, 03:32 PM
The problem is that it is a system, not individual stars. Systems of stars orbit each other. Right now, proxima is the closest, but only because it is at a point in its orbit that makes it closer. This will not always be the case.

Wikipedia (http://en.wikipedia.org/wiki/Proxima_Centauri): "Proxima Centauri may be in orbit about Alpha, with an orbital period on the order of 500,000 years or more." But then, "Proxima Centauri has been the closest star to the Sun for about the last 32,000 years and will be so for about another 9,000 years, when it will be replaced by Barnard's Star."

I think one just has to supply a "right now" (and a "known") when speaking of a closest star to the Sun, and not care too much about an uncertain orbit that might be so long as to make the issue moot.

tony873004
2007-Aug-29, 09:27 PM
Proxima might not even be bound to Alpha Cen A & B. It shares a proper motion in the sky, but at its distance from the AB pair, it should have been stripped away by now.

I can see referring to the AB pair as a single star, since the naked eye can only resolve them as 1 star. Most stars that we refer to are actually a multiple system. For example, when we talk about Polaris, we are actually talking about a 3-star system.

But Proxima is about 2 degrees away from the AB pair. If it were bright enough to be seen with the naked eye, it certainly would be considered a seperate star.