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Mira, ο Ceti (Omicron Ceti ) is a double star in the constellation Cetus, consisting of the red giant Mira A, or simply Mira and the White Dwarf Mira B or VZ Ceti. Mira A is a variable star and namesake for the Mira stars. Mira is approximately 300 light years away from Earth.

Mira A is a red giant of spectral type M ( Hipparcos database). You changed during a period of about 331 days their luminosity by up to 8 size classes. Neither the period nor the Helligkeitsminima minima and maxima are constant. At the maximum, it can reach the second size class is then a striking bright star in the night sky. While the minimum brightness may drop down to the 9th magnitude, so that their observation a telescope is required. Mira times brighter than their absolute minimum in absolute maximum 1700 - however, in the infrared region in which the majority of the Mira emits radiation, it is at the maximum only by a factor of six as in the light minimum.

Mira has an average diameter of about 400 solar diameters ( about 550 million km). At a distance from Earth of about 300 light years, the Hubble Space Telescope can resolve the star in terms of area, so this is not only recognizable as a point.

Mira was discovered by the priest and Frisian amateur astronomer David Fabricius on August 13, 1596th In 1639, then discovered Johann Ph. Holwarda that Mira changes its brightness more or less regularly. Because of this strange property of the Star by Johannes Hevelius got its name - Mira, the " Miraculous ". 1923, by R. G. Aitken a faint companion ( VZ Ceti ) found that orbits Mira with a period of about 500 years. 2007 was discovered on images taken by the NASA space telescope GALEX that as yet only known star Mira has a huge tail, which is similar to a comet and extends over 13 light years in length. The unusual structure is the result of the high relative velocity of 110 km / s from Mira compared to the interstellar medium.