EarthSky

December 1st, 2011 - Tonight

If you look towards the southeast tonight in late evening, you will find the brighter of the two Dog Stars, Sirius. This star also happens to be the brightest of all the stars we see in our night sky. Sirius makes up the neck of the constellation Canis Major, the Larger Dog.

Also bright in the sky, although less so than Sirius, is the star Adhara, which makes up the Larger Dog’s bottom right foot. Although it’s true that Sirius has the brightest _apparent magnitude_ of all the visible stars, Adhara actually has a brighter _absolute magnitude_ than Sirius. In other words, Sirius looks bright to us because it’s closer. But if the two stars were observed at an equal distance from Earth, Adhara would appear brighter than Sirius.

Apparent magnitude is the measure of brightness of a star as seen from Earth at the star’s natural distance. Absolute magnitude is the measure of the brightness of a star as seen from Earth if the star were placed at a distance of 32.6 “light-years”:http://earthsky.org/article/49016/how-far-is-a-light-year from the Earth. So, while Sirius may be the brighter star, this is not because it is intrinsically more luminous. It is because Sirius is much closer to the Earth than Adhara.

We hinted that Sirius isn’t the only Dog Star in our sky – and it’s true. The other one is Procyon in the constellation Canis Minor the Lesser Dog.