Mira


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Mira

(mī`rə), [Lat.,=marvelous], variable starvariable star,
star that varies, either periodically or irregularly, in the intensity of the light it emits. Other physical changes are usually correlated with the fluctuations in brightness, such as pulsations in size, ejection of matter, and changes in spectral type, color, or
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 in the constellation Cetus; Bayer designation Omicron Ceti; 1992 position R.A. 2h19.0m, Dec. −3°05'. The most famous long-period variable, Mira ranges in apparent magnitudemagnitude,
in astronomy, measure of the brightness of a star or other celestial object. The stars cataloged by Ptolemy (2d cent. A.D.), all visible with the unaided eye, were ranked on a brightness scale such that the brightest stars were of 1st magnitude and the dimmest stars
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 from a maximum of about 2.0 to a minimum of about 10.1 with a period of a little less than a year (332 days). Thus, it is visible to the naked eye for about half a year and can be seen only through a telescope for the remainder of its period. Mira is of spectral classspectral class,
in astronomy, a classification of the stars by their spectrum and luminosity. In 1885, E. C. Pickering began the first extensive attempt to classify the stars spectroscopically.
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 M6e III, the spectrum showing some emission lines. There is some variation in maximum brightness that is thought to be due to clouds of hydrogen gas surrounding the star. Mira's distance from the earth is about 100 light-years.
Light curve of Miraclick for a larger image
Light curve of Mira

Mira

or

Mira Ceti

(mÿ -ră, meer see -tÿ, set -ee) (the Wonderful; ō Cet) A red giant in the constellation Cetus that is a long-period variable star with an average period of 331 days. It was known to early astronomers for its regular appearances and disappearances and was established in 1638 as a variable star. It is the prototype of the Mira stars. Its radius varies by 20 per cent during its cycle and at maximum size and brightness is over 330 times the Sun's radius. The surface temperature varies from about 2600 K at maximum luminosity down to about 1900 K. The visible light emitted varies considerably, usually by about 6 magnitudes, over the cycle (see illustration). The average maximum apparent magnitude, m V, lies between 3 and 4 although it may reach 2nd magnitude. At minimum it is about 8th to 10th magnitude. Mira is also an infrared source, the emission arising from dust grains in the expanding envelope of gas.

Mira is both a visual binary with a faint peculiar companion that is also variable, and an optical double. MV : –1.0 (var.); spectral type: M6e–M9e III; distance: 40 pc.

Mira

 

(o Ceti), the first known variable star; discovered as a variable star in 1596 by D. Fabricius. Mira varies in brightness from a stellar magnitude of 2.0 to a stellar magnitude of 10.1, with a period averaging 331.5 days. The variations in brightness are due to the pulsations of the star, as a result of which the diameter varies by approximately 10 percent, which is accompanied by a variation in the temperature and brightness of the star’s surface. Mira measures about 500 million km in diameter and is located 77 parsecs from the sun.

Mira

[′mir·ə]
(astronomy)
The first star recognized to be a periodic variable; has a period of 332 ± 9 days and its spectrum changes from M5e at maximum to M9e at minimum;it is the prototype of long-period variable stars.
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