At night you can’t miss the spectacle of looking for and seeing Sirius, the brightest star in the night sky. Is it the brightest star? Yes and no. For astronomers, the word luminous refers to the intrinsic brightness of a star. To clarify, Sirius is the brightest star in our sky (although not as bright as the planets Jupiter and Venus, of course), but it is not the brightest star in the sky. In other words, it is an ordinary star that only seems very bright to us because it is relatively close to us: eight light years away.
Sirius is in the constellation of the southern hemisphere of Canis Maior, and looks extraordinarily bright in the Earth’s sky. No matter where you live on Earth, follow the three medium-bright stars on Orion’s Belt to locate Sirius.
Sirius is more than 20 times brighter than our Sun, and more than twice as massive.
Many people say they see Sirius with flashes of various colors. It happens when you see Sirius low in the sky. Colours are simply the colours of the ordinary rainbow in the white light of the stars. All stellar light is composed of this mixture of colors. However, we notice the bright colors of Sirius more easily because it is much brighter than most stars. The extra thickness of the Earth’s atmosphere near the horizon acts like a lens or prism, breaking the stars’ light into the colors of the rainbow. When you see Sirius low in the night sky, you are looking through more atmosphere than when the star is high.
If you stay looking, you will notice that Sirius shines less and looks less colorful (more strictly white) when it appears higher in the sky.