Mira double star. Hubble Space Telescope image of the double star Mira (Omicron Ceti). Mira A (right) is a variable red giant star that changes in brightness by a factor of around 1700 over a period of some 331 days. Its companion star (left) is a small, hot white dwarf. The two stars are separated by around 10.5 billion kilometres (about 70 times the Earth-Sun distance). Mira is a huge star, around 700 times the size of the Sun. It changes shape and size during its period. The Mira system is thought to lie around 420 light years from Earth in the constellation Cetus. Image taken by the Faint Object Camera on the HST.