The closest stars
Published on Mar 17, 2006 at 11:07 am.
5 Comments.
Filed under stars.
What are the nearest stars, and where are they? This is a question that I am frequently asked. So, I thought that I might say a few words along this line. The Sun is obviously the nearest star, but I won’t count that. We are talking here about the stars nearest the Sun.The nearest star is Rigel Kentaurus, the foot of the Centaur. Being fairly close, it is no surprise that this is also one of the brighter stars in the sky. Often, to avoid confusion with the Rigel in Orion, Rigel Kentaurus is referred to by its Bayer designation: Alpha Centauri. Centaurus is a far southern constellation, so most of my readers in the northern hemisphere will never see Alpha Centauri. You must be a ways south of 29 degrees north latitude to see this star. The farther south, the better. My Australian readers, though, have a bird’s eye view, though. It passes high in the sky there around midnight this time of the year. During your winter, it will be high in the sky a little after sunset. Alpha Centauri is actually a triple star system. The stars orbit one another fairly close together, and a third red dwarf star orbits the pair much farther out. Currently, this red dwarf if the closest of the three stars and it is called Proxima Centauri. It is actually far enough from the others that you’d be able to see it as a separate star to the naked eye if only it were bright enough. It is a pretty small and dim star, though, about 250 times dimmer than the naked eye can see.
The second closest star is called Barnard’s star. Barnard’s star is famous as being the star with the highest measured proper motion. Proper motion is the apparent motion of the star through the sky. So, if you wait a few years, the coordinates of Barnard’s star change. If you wait long enough, it will even drift into another constellation. Don’t hold your breath, though, because even with its rather large proper motion, it still takes somewhere around 175 years to move through the sky a distance that appears the same as the width of the full moon. Barnard’s star is located in the constellation Ophiuchus. This constellation is visible in the summer time here in the northern hemisphere, but don’t expect to see the star. It would have to be about 25 times brighter to even make it as bright as the dimmest star the unaided eye could see (and that from a dark sky!). The third closest star is Wolf 359. It is so dim that it didn’t make any of the other catalogs that I discussed months ago. It would need to be nearly 1000 times brighter to be barely visible to the naked eye. If you could see it, then Wolf 359 would be in the southern part of Leo. An interesting sidebar on this star is that it was featured in Star Trek the Next Generation. This is the star where the Borg cube wiped out the Federation fleet sent to stop it.
The fourth closest star is a fairly new one on the list. That isn’t because it recently moved close. Rather it is another really dim one that was not discovered until recently. It is known by its catalog designation: 2MASS 0253+16. It is located in Aries. At magnitude 15.4, it would need to be nearly 400 times brighter in order to see with the naked eye. It, like Wolf 359 and Barnard’s star, is a red dwarf. The fifth closest star is BD+36°2147. Compared with the previous stars this one is pretty bright, being only one fourth the dimmest that the naked eye can see. It is another red dwarf star, and it is located in Ursa Major. The sixth nearest star is Sirius. Finally another bright one! Sirius, located just southeast of Orion is the brightest star in the sky (other than the Sun, of course!). Sirius is a white hot type A star Sirius is also a binary star, but its companion is a strange beast. Sirius B is a white dwarf star. That is what is left when a star like the Sun or up to about 6 or 7 times the mass of the Sun leaves when it dies. So, Sirius is a system with a bright white star with a dead star orbiting it. Now, I could keep going on. I’ve got a list of the 50 nearest stars at my fingertips, and I can find a list of the nearest 1000 stars if I look a little for it. I’d imagine that it would get pretty boring to keep going on, though. However, I’ll give you a taste of the next few stars. After Sirius, the next three are again red dwarf stars too dim to see with the naked eye. Then comes one, Epsilon Eridinii, that is visible to the naked eye, but is a rather dim star and not visible from most light polluted skies. Then there are three more too dim to see with the naked eye, followed by one barely visible to the naked eye, followed by Procyon, another rather bright star. Then there are more dim red dwarf stars, too dim to see with the naked eye, and so it goes.
So, what gives with all the red dwarf stars? Well, as it turns out, they are the most common star out there. Red dwarf stars are easy to form, so they form more often than other stars. They are very low mass stars, so they are small and cool. They don’t fuse hydrogen very quickly because they don’t much mass to support, so they live a long time. In fact, the average lifetime of a red dwarf star is probably 100 times the current age of the universe! So, any that ever formed are still around. Because they are so dim, though, we are only guessing how many are out there. We can only detect the ones that are closest to us, and then even with difficulty. As I indicated, one has been right on our doorstep and we never knew it until recently. How many others are lurking nearby? Many astronomy books begin the chapter on the Sun with a phrase that goes something like, The Sun is a typical star. This mistakenly gives students the impression that most stars are like the Sun. Actually, the Sun is more massive and brighter than about 85% of the stars out there. Not even the stars that you see in the sky are like the Sun. Most of the stars that you see are the unusually bright stars, many of which shine with hundreds, thousands, or even tens of thousands of times the Sun’s luminosity. That is why you see them from so far away. Making the Sun even rarer is that it is a single star. Most stars of the Sun’s type are found in binary star systems. This makes the Sun and Earth a rather uncommon system. For various reasons, we expect to find the conditions most likely suitable for life to be on a planet about the size of the Earth about the distance of the Earth from a star about like the Sun. Unlike how science fiction often portrays a galaxy filled with planets teaming with life, the Sun appears to be a special case. We don’t really know enough about planets to tell if Earth is a special case, too, but my personal belief is that it is. Thus, the conditions for advanced life out there would seem to be rare. Civilizations of intelligent beings are likely pretty rare in the galaxy. With luck, we’ll eventually become one. 
-Astroprof
caleb on February 6, 2008 at 4:54 pm: 1
Hi there. I’m currently working on a sound piece which requires finding a list of the nearest 870 stars to earth. Where could I find a resource that would give me catalogue names for these? hope you can help! regards, caleb
Astroprof on February 6, 2008 at 5:45 pm: 2
Hmm. I don’t know of a list of nearest stars that is that long. However, you can access an astrographic catalog, like the USNO CCD Astrograph Catalog and search for the nearest stars.
Iskandar Ibrahim on March 14, 2008 at 5:46 am: 3
Please advise :
1. How information about stars you describe will IMPACT to the surrounding of supernovas the stars will go through upon the end of their life time.
2. Eta Carina was published by astronomy to have been undergoing a supernova ? But you did not say anything or comment on that; did I or any body miss reading about it ?
3. Say something about the Solar Systems, at about the time it will go to Supernova conditions. Say something of the impact of such event to Solar _ Earth life, science & status, what thence.
Astroprof on March 14, 2008 at 2:40 pm: 4
Eta Carinae did not go supernova. However, it did undergo a major mass ejection event last century (a far, far smaller explosion than a supernova). It is a future candidate for something perhaps even larger than a traditional supernova: a hypernova. I wrote about that in another posting. This one was limited to just nearby stars, and Eta Carinae is quite far away. Oh, and the Sun will never go supernova. Only really massive stars, at least ten to fifteen times the mass of the Sun, have a chance to go supernova.
Astroprof’s Page » The Five Brightest Stars on September 6, 2008 at 1:36 pm: 5
[…] stars, even those very nearby, could never be seen with the naked eye. About a month ago, I did a blog entry on the nearest stars. I sort of envy those of you living in the Southern hemisphere, because you […]