Sirius

Canis Major and Canis Minor

Sirius (at the lower right of the photo) of course is the brightest star in the sky after our Sun, and being an astronomer it provides me with a lot of interaction from the general public.   Every spring it seems I get several calls from people saying that they saw some sort of UFO in the southwestern sky in the evening.  It blinks and flashes different colours at them and appears to follow them.  With a little investigation, the object is identified as Sirius.   When it is higher in the sky in the early spring it is rarely unidentified. As I mentioned in an earlier post, Sirius was used by the Polynesians to navigate.  In fact it is the zenith star of Tahiti.   That means that if Sirius passes directly over your head, then you at at the latitude of Tahiti.  Quite useful if you are lost on the Pacific Ocean.

Sirius is actually two blue-white stars in orbit around each other.  The brighter is a main sequence star about twice as massive as the sun.  The fainter is a white dwarf star about as massive as the Sun but with the radius of the Earth.  Sirius B presented a great problem for physics that was only solved by quantum mechanics, nearly a century after its discovery.   Sirius A and B are two of the eight closest stars to the Sun, so white dwarfs clearly a common in the sky which only made the problem more frustrating. Although Sirius B is much fainter in the optical, it dramatically outshines Sirius A in the x-rays.  And there is possibly a habitable zone for planets that orbit around both stars but no potential Tatooines have been discovered.