Mira

Mira (ο Cet / ο Ceti / Omicron Ceti) is a binary star in the constellation Cetus consisting of the red giant, Mira A or just Mira, and a white dwarf, Mira B or VZ Ceti. Mira A is also an oscillating variable star and was the first non-supernova variable star discovered, with the possible exception of Algol. Apart from the odd Eta Carinae, Mira is the brightest periodic variable in the sky that is not visible during part of its cycle.

Related Topics:
Omicron - Binary star - Constellation - Cetus - Red giant - White dwarf - Variable star - Supernova - Algol - Eta Carinae

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The companion star was resolved by the Hubble Space Telescope in 1995, when it was 70 astronomical units from the primary; results were announced in 1997. The HST ultraviolet images and later X-ray images by the Chandra space telescope show a spiral of gas rising off Mira in the direction of Mira B. The companion's orbital period around Mira is approximately 400 years.

Related Topics:
Hubble Space Telescope - 1995 - Astronomical unit - 1997 - Chandra space telescope - Orbital period

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Mira became the "type" star of the long-period "Mira variables". It — and the other 6000 or so known stars of this class — are all red giants whose surfaces oscillate in such a way as to increase and decrease in brightness over periods ranging from about 80 days to more than 1000. In the particular case of Mira, its increases in brightness take it up to about magnitude 3.5 on average, which is a fairly noticeable star. Individual cycles vary too; well-attested maxima go as high as magnitude 2.0 in brightness and as low as 4.9, a range almost 15 times in brightness, and there are historical suggestions that the real spread may be three times this or more. Minima range much less, and have historically been between 8.6 and 10.1, a factor of four times in luminosity. The total swing in brightness from absolute maximum to absolute minimum (two events which did not occur on the same cycle) is 1700 times. The shape of its light curve is of an increase over about 100 days, and a return twice as long. A recent lightcurve is available from the BAV (http://www.bav-astro.de).

Related Topics:
Mira variable - Light curve

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