Polaris

Polaris (α UMi, α Ursae Minoris, Alpha Ursae Minoris, commonly North(ern) Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star. Polaris is about 434 light-years from Earth and is a multiple star. It consists of the main star α UMi A, two smaller companions, α UMi B and α UMi Ab, and two distant components α UMi C and α UMi D. α UMi B was discovered in 1780 by William Herschel. α UMi A is a six solar mass F7 bright giant (II) or supergiant (Ib). The two smaller companions are: α UMi B, a 1.5 solar mass F3V main sequence star orbiting at a distance of 2400 AU, and α UMi Ab, a very close dwarf with an 18.5 AU radius orbit. There are also two distant components α UMi C and α UMi D. Polaris B can be seen even with a modest telescope and was first noticed by William Herschel in 1780. In 1929, it was discovered by examining the spectrum of Polaris A that it had another...