Omicron Ceti


Distance (Light Years) 419 ± 58
Apparent Magnitude 6.47
Color (B-V)1.42

Names For This Star

The name of the star is the feminine form of a Latin adjective meaning "Wonderful." This name is probably an abbreviation of Stella Mira, "The Wonderful Star", which Allen gives as an alternative name for the star. Allen also offers the Latin Collum Ceti, "The Neck of the Whale" as another alternative name for the star.

Description of the Star

Mira Type Variables

Mira is a type M red giant star. It is the prototype star for the long period "Mira" variables. Mira variables vary in brightness by typically 5 to 6 magnitudes, but sometimes as much as 9 magnitudes. The period of such a star lies in the range typically from 60 to 700 days, but a few stars lie outside these limits. The period tends to be somewhat irregular.

The period for Mira averages about 331 days according to Burnham. At its brightest Mira typical appears at a visual of about 3.5, but the brightness at both maximum and minimum fluctuates. Mira might be seen as bright as magnitude 2.5 at maximum. At minimum, the Apparent Magnitude averages 9.30, but the minimum brightness has been observed to be as bright as magnitude 8.60 or as dim as magnitude 9.60.

Mira's Diameter

The measured diameter of the star is about 7 AU, that is, about 670 million miles, or something greater than the diameter of the asteroid belt in between the orbits of Mars and Jupiter in the solar system. The diameter of the star can be expected to fluctuate as the brightness of the star varies.

Variation in Temperature and Spectral Type

The variation in the brightness of Mira is accompanied by changes in temperature and spectral type. Near brightness maximum, the spectrum would be that of an M6III star, with a temperature of around 2500 K according to Burnham. Near minimum brightness, the temperature of the star as fallen to about 1900 K with a spectral type of M9III, making the star one of the coolest stars known.

Mira's Companion Star

The long period variable is actually Mira A. There is a companion, Mira B, that is much smaller in size than A.

The companion is a blue type B dwarf, that revolves in a 400 year orbit about A at a distance of more than 100 AU. According to the The Bright Star Catalog, the Mira A is about 15.7 times as massive as the sun, while B is 4.0 times as massive.

Other Designations For This Star


68 Ceti

Hipparcos Identifier (HIP Number)


Harvard Revised (HR Number)


Henry Draper Catalog (HD Number)


Bonner Durchmusterung (BD Number)

BD-03 353
Smithsonian Astrophysical
Observatory compendium (SAO Number)

Fundamental Katalog (FK5 Number)



Copyright © 1998 - 2010 by Arnold V. Lesikar,
Professor Emeritus
Dept. of Physics, Astronomy, and Engineering Science,
St. Cloud State University,St. Cloud, MN 56301-4498

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