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Mira
Mira (, also known as Omicron Ceti, ο Ceti, ο Cet) is a red giant star estimated 200–400 light years away in the constellation Cetus. Mira is a binary star, consisting of the red giant Mira A along with Mira B. Mira A is also an oscillating variable star and was the first non-supernova variable star discovered, with the possible exception of Algol. Mira is the brightest periodic variable in the sky that is not visible to the naked eye for part of its cycle. Its distance is uncertain; pre-Hipparcos estimates centered on 220 light-years; while Hipparcos data from the 2007 reduction suggest a distance of 299 light-years, with a margin of error of 11%.〔http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Omicron+Ceti&submit=SIMBAD+search〕
==Observation history==
Evidence that the variability of Mira was known in ancient China, Babylon or Greece is at best only circumstantial. What is certain is that the variability of Mira was recorded by the astronomer David Fabricius beginning on August 3, 1596. Observing what he thought was the planet Mercury (later identified as Jupiter), he needed a reference star for comparing positions and picked a previously unremarked third-magnitude star nearby. By August 21, however, it had increased in brightness by one magnitude, then by October had faded from view. Fabricius assumed it was a nova, but then saw it again on February 16, 1609.
In 1638 Johannes Holwarda determined a period of the star's reappearances, eleven months; he is often credited with the discovery of Mira's variability. Johannes Hevelius was observing it at the same time and named it "Mira" (meaning "wonderful" or "astonishing," in Latin) in his ''Historiola Mirae Stellae'' (1662), for it acted like no other known star. Ismail Bouillaud then estimated its period at 333 days, less than one day off the modern value of 332 days. This is likely to be not only perfectly forgivable, but also quite accurate; Mira is known to vary slightly in period, and may even be slowly changing over time. The star is estimated to be a 6-billion-year-old red giant.
There is considerable speculation as to whether Mira had been observed prior to Fabricius. Certainly Algol's history (known for certain as a variable only in 1667, but with legends and such dating back to antiquity showing that it had been observed with suspicion for millennia) suggests that Mira might have been known too. Karl Manitius, a modern translator of Hipparchus' ''Commentary on Aratus'', has suggested that certain lines from that second-century text may be about Mira. The other pre-telescopic Western catalogs of Ptolemy, al-Sufi, Ulugh Beg, and Tycho Brahe turn up no mentions, even as a regular star. There are three observations from Chinese and Korean archives, in 1596, 1070, and the same year when Hipparchus would have made his observation (134 BC) that are suggestive, but the Chinese practice of pinning down observations no more precisely than within a given Chinese constellation makes it difficult to be sure.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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