mercredi 3 septembre 2008

Cetus 5



Diphda
Beta Ceti


Distance (Light Years)
96 ± 2
Visual Magnitude
2.04
Color (B-V)
1.02
Names For This StarThis star is also known as Deneb Kaitos, Difda, Difda al Thani, or Rana Secunda.
The name Deneb Kaitos derives from the Arabic Al Dhanab al Kaitos al Janubiyy, "The Tail of the Whale Towards the South."
The names Diphda, Difda and Difda al Thani come from the Arabic name Al Difdi` al Thani meaning "The Second Frog."
Rana Secunda is a Latin translation of Al Difdi` al Thani.
For the Arabs Diphda was the Second Frog with Fomalhaut as the First Frog.
Description of the StarThe The Bright Star Catalog gives the spectral type of Diphda as G9.5IIICH-1. Burnham" classifies the star as K1III, while the "Hipparcos Catalog" offers a classification of K0III. All of these classifications indicate a yellow-red giant star at about 4500 K and about 4 times the mass of the sun.
Diphda is about 110 times as luminous as the sun.




Menkar
Alpha Ceti


Distance (Light Years)
220 ± 12
Visual Magnitude
2.54
Color (B-V)
1.64
Names For This StarOther names for this star are Mekab, Menkab, and Monkar. These names derive from the Arabic name for the star, Al Minhar, "The Nose (of the Sea Monster)."
Description of the StarMenkar is a cool, red M1.5IIIa giant having a luminosity about 380 times that of the sun.



Mira
Omicron Ceti


Distance (Light Years)
419 ± 58
Visual Magnitude
6.47
Color (B-V)
1.42
Names For This StarThe 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 VariablesMira 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 Visual 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 DiameterThe 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 TypeThe 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 StarThe 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.

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