Mira variable star. Hubble Space Telescope image of the star Mira (Omicron Ceti). It is a variable red giant star that changes in brightness by a factor of around 1700 over a period of some 331 days. Mira is a huge star some 700 times the size of the Sun. It has an irregular shape, possibly an effect of its rapid expansion and contraction. It has a white dwarf companion star (not seen) separated from it by around 10.5 billion kilometres (some 70 times the Earth-Sun distance). 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.