Is the brightest star in the night time sky truly the biggest, hottest and brightest star in the Milky Way?
1 Answer
No, the brightest star in the night sky is Sirius which is not the brightest star in the Milky Way.
Explanation:
The brightness of a star in the sky is determined by the actual brightness of the star and its distance away. Distant stars appear much dimmer than closer stars.
The brightness of a star in the sky is measured as its apparent magnitude. This is a logarithmic scale where a difference of 5 means the star appear 100 times brighter. So, a magnitude 1 star is 100 times brighter than a magnitude 6 star.
Astronomers need to now how bright a star really is. So a star has a second brightness value called its absolute magnitude. The absolute magnitude is how bright a star would appear if it was 10 parsecs away.
For reference the Sun has an absolute magnitude of 4.2.
The brightest star in the night sky is Sirius which has an apparent magnitude of -1.46 and an absolute magnitude of 1.4. It is 8.6 light years away. It is 25 times brighter than the Sun.
Compare this to the star Rigel which has an apparent magnitude of 0.12 and an absolute magnitude of -8.1. It is 1,400 light years away. It is 120,000 times brighter than the Sun.
So, Rigel is almost 4,800 times brighter than Sirius but is it some 160 times further away.
