Brightest Star | Universe Today

Written by Jerry Coffey

Have you ever wondered which is the brightest star in the night sky? A lot of people have, but the question is not necessarily easy to answer. There are two ways to measure the brightness of a star: apparent magnitude and absolute magnitude. Apparent magnitude measures how bright from Earth. Absolute magnitude measures how bright a star is from 10 parsec away. Based on that the Sun has a apparent magnitude of -26.8 and an absolute magnitude of 4.75. If you are measuring stars by their apparent magnitude, the brightest star is Sirius at a magnitude of -1.46. If you measure by absolute magnitude, the brightest star is Pistol.

Sirius, the brightest star by apparent magnitude, is is actually a binary star system, consisting of a white main sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. Sirius appears bright due to its intrinsic luminosity and its closeness to the Earth( 2.6 parsecs). Sirius A is about twice as massive as the Sun and has an absolute visual magnitude of 1.42. It is 25 times more luminous than the Sun, but has a significantly lower luminosity than other bright stars such as Canopus or Rigel. The system is between 200 and 300 million years old. It was originally composed of two bright bluish stars. The more massive of these, Sirius B, consumed its resources and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago.

The Pistol star is the brightest star if when measured by absolute magnitude. It is thought to be a member of the Quintuplet cluster. It is 25,000 light years from the Earth and about 100 light years from the center of the Milky Way galaxy. The Pistol shines 10,000,000 times brighter than our Sun. That is only an estimate. True values are hard to come by because of the amount of dust between here and the star and the huge amount of stellar wind that the star produces. The winds have a cooling effect on the star and alters its luminosity.

Here on Universe Today we have an article that tells you about several of the brightest stars in the night sky. Astronomy Cast offers a good episode about many of the most famous stars in the heavens. Here is a link to a great article about the Pistol star.

Filed under: Astronomy

Tags: brightest star, Sirius, the Pistol star