I am sure most of us would like to take a walk around our home on pleasant summer day like today. When you go out, you might see the neighborhood kids biking on the side walk. You might even see some neighbors walking their pets. You might stop to exchange a few pleasantries with people whom you know. You will see blooming flowers, in the bright summer air.
But, just for a moment, imagine that when you take your walk there is nothing around. The only thing you see is a dim light afar. You walk towards it; you do not meet anyone on the way. You have walked more than 4 miles, to your surprise you find a he toddler crawling slowly on the ground. Then you look around; The light you were following all this time is much more closer now, and you can see a couple standing below the light pole. Could they be his parents? Do you think if such a neighborhood be interesting? Do you find it creepy? Are you willing to take a bet that such a neighborhood does not exist?
Don’t take that bet! Because that is exactly like the interstellar neighborhood we live, or rather our Sun lives in. The Sun is an average star – meaning when compared with the bulk of stars in the Milky Way it is neither very big, nor too small. It is not one of the hottest stars and not one of the coolest. It is not a very old star nor is it very young.
The solar neighborhood is typical of what you would find on the periphery of the galaxy. The stars are packed very loosely. If you take s sphere of radius of about 20 light years around the Sun, there are only about 100 stars!
The scene I described before is a solar analogy. The slowly crawling toddler 4 miles away from your home is Proxima Centauri. in the constellation of Centaurus. This is the nearest star to the Sun at a distance of about 4.2 light years. This star is much cooler than the Sun and has a diameter 1/7th that of the Sun. Proxima Centauri is not even visible to the naked eye, with a brightness 100 times dimmer than the faintest stars that we can see with the naked eye.
This dwarf is orbiting a star pair, called Alpha Centauri. Many of the bright stars have proper names, otherwise they are referenced by the constellation they belong to, normally with a Greek prefix. Generally, the brightest star in a constellation is termed Alpha. Alpha Centauri is the brightest star in the constellation Centaurus.
Many stars that we see are in fact multi-star systems. The stars that constitute Alpha Centauri, generally termed Alpha Centauri A and Alpha Centauri B and these are analogous to the couple I mentioned before. These two stars are both very much like the Sun. When seen by the naked eye, Alpha Centauri looks like a single bright star, and it is the third or fourth brightest star as seen from the Earth. Because of it’s location in the celestial southern hemisphere, it is not visible from large parts of northern hemisphere. The pair forming Alpha Centauri is located about 4.4 light years away from the Sun.
Who comes next in the list of our neighbors? It is Barnard’s Star – another dim star about 6 light years away. This is at least 15 times dimmer than the dimmest star we can see with bare eyes. The Star is named after an astronomer who first identified this star. We all know that stars are fixed points in the sky. But the truth is that all stars, including our Sun, are moving. We can not notice the change in the positions of the stars because of the large distances involved. In case of Barnard’s Star, it has perceptible movement and within your life time you will be able to see the change in its position in the sky with respect to other stars. Because of this fact, it is also called the Running Star or the Flying star. In fact, it is moving so fast that in another 10000 years, it would be replacing Proxima/Alpha Centauri system as the closest neighbor of the Sun.
The next closest star Wolf 359 is rather an uninteresting dim star named after a scientist. After this, at 8.3 light years is Lanande 21185. This is dwarf star, and an interesting one. Scientists have evidence to believe this star has 2 planets comparable to the size of the Jupiter in our solar system.
Little further, at around 8.6 light years we find Sirius, the brightest star in the night sky, and is about 30 times larger than the Sun. This brightness attracted all ancient civilizations. It is called vyAdha in Samskrita, Al Shira in Arabic and Tian Lang in Chinese. Ancient Egyptians found out that the annual flooding of the Nile occurred when this star appeared in the sky just before sunrise, and so it became quite an important star to them. Sirius is also a binary system, but in this case, one of the stars, Sirius A is a huge star, while B is a dwarf star.The star is part of Canis Major constellation and called Alpha Canis Majoris and in common usage, the star is called the Dog Star.
Let’s skip a few more naked eye-invisible stars and come to the next naked eye star. This is Epsilon Eridani located at about 10 light years. It is similar to the size in Sun, but only quarter as bright. What is special about this star? Well. It turns out that this star too has a planetary system, with at least two planets!
We went around our solar neighborhood. We found all kinds of stars, big and small. Bright and dim. We visualized how space is very sparsely populated. We also saw that planetary systems are not unique to our Sun. So could life be? That is a question only future can answer.
I enjoyed waking in this stellar neighborhood. And hope you did too!
(p.s: This was a speech I gave in one of the meeting of our Toastmasters Club)