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Alpha Cassiopeiae
Alpha cassiopeiae diagram.jpg
Star map of the Bayers Stars in Cassiopeia. Alpha Cassiopeiae is circled.
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension 00h 40m 30.5s
Declination +56° 32′ 14.5″
Apparent magnitude (V) 2.24
Characteristics
Spectral type K0 IIIa
U-B color index 1.13
B-V color index 1.17
Variable type Suspected
Astrometry
Radial velocity (Rv) −3.8 km/s
Proper motion (μ) RA: 50.36 mas/yr
Dec.: −32.17 mas/yr
Parallax (π) 14.27 ± 0.57 mas
Distance 229 ± 9 ly
(70 ± 3 pc)
Absolute magnitude (MV) −1.99
Details
Mass 4–5 M
Radius 42 R
Luminosity 855 L
Temperature 4,530 K
Metallicity ?
Rotation 21 km/s
Age ? years
Other designations
18 Cassiopeiae, HR 168, BD+55°139, HD 3712, SAO 21609, FK5 21, HIP 3179, GC 792, ADS 561, CCDM J00405+5632

Coordinates: Sky map 00h 40m 30.5s, +56° 32′ 14.5″

Alpha Cassiopeiae (α Cas / α Cassiopeiae ) is the second-brightest star in the constellation Cassiopeia (magnitude 2.25). It has the traditional name Schedar (which may also be spelt as Shedar, Shadar, Schedir, or Shedir).

It is an orange giant (spectral type K0 IIIa), a type of star cooler but much brighter than our Sun. In visible light only, it is well over 500 times brighter than the Sun. According to the Hipparcos astrometrical satellite, distance to the star is about 230 light years (or 70 parsecs).

Schedar has been sometimes classified as a variable star, but no variability has been detected since the 19th century. Also, three companions to the star have been listed in the Washington Double Star Catalog, but it seems that all of them are just line-of-sight optical components.

The name Schedar comes from the Arabic word صدر şadr, "breast".

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