Looking Up: Hamal Is A Special Star, Just Like Every Star

Oct 8, 2018

Hamal – also known as Alpha Arietis – shines as the brightest star in the constellation Aries the Ram (derives from the Arabic for 'head of the ram').
Credit public domain / Creative Commons

This week on Looking Up Chloe Brooks-Kistler returns as guest host with some info on Hamal, a protoype orange giant star.

Today’s edition of Looking Up is going to be, well, very average. And that’s because the subject of today’s episode is a very average star named Hamal. But in this case, being average is very, very helpful to astronomers. Let me tell you why.

Hamal is the brightest star, at magnitude 2.0, in the Fall constellation of Aries, the Ram. If you go back a couple thousand years, Hamal was very close to the point on the celestial equator where the Sun crosses, turning summer to fall. But because the Earth wobbles, that point is now in a different constellation altogether. So, it’s not special because of its location. In fact, it’s not special at all, which makes it, well, special!  

It seems that Hamal is the absolute prototype for an orange giant star. About 90 times brighter than our Sun, astronomers have been able to calculate its temperature very accurately – 7802 F – which in turn leads to even more calculations. Including letting us measure the diameter of the star very accurately. We know that Hamal has an angular diameter – as seen from Earth – of .00680 degrees. Put another way, Hamal is the size of a penny viewed from 37 miles away. That’s pretty precise, I think, but that’s just my two cents. 

Nowadays the sun passes in front of the constellation Aries from about April 19 to May 13.
Credit earthsky.org

If you’d like to take a closer look at Hamal, or any of the other wonderful and amazing things in the sky, please visit csastro.org for a link to information on our monthly meetings and our free public star parties!