Polaris is the brightest star in the constellation Ursa Minor and the 45th brightest star in the night sky. It is very close to the north celestial pole and is commonly used for navigation. Thus, it is also commonly known as the pole star, loadestar, or guiding star.
Star system of Polaris
It is actually a multiple-star system. It consists of one main star, Alpha Ursa Minoris (UMi) Aa and two smaller companions, Alpha UMi AB. There are also two distant components, Alpha UMi C and Alpha UMi D.
Classification and characteristics
Alpha UMi Aa is a yellow supergiant with a mass 4.5 times that of the Sun. The two smaller companions are as follows:
•Alpha UMi B – is a main-sequence star orbiting at a distance of 2400 AU and a mass 1.39 times that of the Sun.
• Alpha UMi Ab – is a very close main-sequence star at a distance of 18.8 AU and a mass 1.26 times that of the Sun.
Alpha UMi Aa is visible to the naked eye and even a modest telescope can see Alpha UMi B. The system is at an approximate distance of 434 light-years from Earth.
Pole star
Because Alpha UMi nearly lies in a direct line with the axis of Earth’s rotation “above” the North Pole, it stands almost motionless in the sky. As a result, all the stars of the Northern sky appear to rotate around Polaris. It makes an excellent fixed point to draw measurements for celestial navigation and astrometry.
The celestial North Pole is not fixed. It moves due to Earth’s motion. As a result, Polaris wants always a pole star and will not be one after a few centuries.
Compiled by: Madhurani Chavan