This Month's Star is Rasalmothallah

This month look for the star Rasalmothallah in the constellation Triangulum, a constellation located between Andromeda and the Pleiades (but closer to Andromeda). Rasalmothallah, an Arabic word, means the triangle. In Latin, the star was called Caput Trianguli, or the head of the triangle. To astronomers, Rasalmothallah is Alpha Trianguli; however, not because it’s the brightest star in Triangulum (which is normally the reason for a star to be designated the alpha star). It’s Triangulum’s alpha star because it’s at the triangle’s apex, or the constellation’s most prominent point. In actual brightness, Alpha Trianguli is the second brightest star of the constellation. Rasalmothallah is the only star in Triangulum with a proper name; the other two bright members are just called Beta and Gamma Trianguli.  

Rasalmothallah is one of the few stars that we can see with our eyes that’s similar to our sun. Rasalmothallah weighs 50% more than our sun, which increases its diameter by three times, its surface temperature by 10%, and its brightness by 13 times compared to the sun. That may make Rasalmothallah seem much bigger and brighter than our sun. However, when compared to the other stars visible to the naked eye, Rasalmothallah and the sun are very much alike. Rasalmothallah is 64 light years away. Therefore, the star light you see tonight left the star in the year 1951.

Rasalmothallah is our guide to finding the Triangulum Galaxy, or M-33, a galaxy about as distant from the Milky Way as the Andromeda Galaxy (around 2.5 million light years away). M-33 is a face-on spiral galaxy, which means it looks like a stellar pinwheel. In dark skies, some people can glimpse M-33 as a dim fuzzy patch. However, because of its large size and low surface brightness, M-33 is best viewed in binoculars rather than in most telescopes.

You’ll find Triangulum high overhead in the south during December nights.