Sirius, a binary star and the brightest star in the night sky

Sirius is a binary star and the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star.
The binary system consists of a main-sequence star of spectral type A0, termed Sirius A, and a faint white dwarf companion of spectral type DA2, designated Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.

If you look carefully at Sirius, you will see it has a slight blue color. If you use a prism to stretch Sirius’s light, you will see that it is not just blueanf that Sirius actually emits a rainbow of colors from violet to red. (It looks blue because the blues are slightly brighter than the other colors.) And, if you look even more carefully at Sirius’s spectrum, you will notice something else: It is not a continuous rainbow. Some of the colors are missing.
These black lines are known as absorption lines, and they are evidence of the chemical elements that make up the star. Each element absorbs a particular set of colors of light, preventing those colors from reaching us. The pattern of absorption lines is like a silhouette or profile that scientists can use to identify the element from millions of miles away. Astronomers can unravel many patterns of absorption lines in a star to figure out what the star is made of. The strong absorption lines in this spectrum of Sirius are from hydrogen, the most abundant element in stars, and in the universe as a whole.

Phedias Hadjicharalambous
Cyprus Astronomy Organisation