α Cassiopeiae is the star's Bayer designation. It bore the traditional name Schedar, which was first encountered in the Alfonsine tables of the thirteenth century. It derives from the Arabic word صدر şadr, meaning "breast", a word which is derived from its relative position in the heart of the mythological queen Cassiopeia. Johannes Hevelius used the name Schedir in his writings, although there were additional traditional spellings of this Arabic transliteration such as Shedar, Shadar, Sheder, Seder, Shedis, and Shedir. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalogue and standardize proper names for stars. The WGSN approved the name Schedar for this star on 21 August 2016 and it is now so included in the List of IAU-approved Star Names. Al-Sufi and Ulug Beg named the star Al Dhāt al Kursiyy, which Giovanni Battista Riccioli changed to Dath Elkarti. In Chinese, 王良 refers to the Chinese asterismWang Liang, a famous charioteer during the Spring and Autumn period. The stellar pattern consists of Alpha, Beta, Kappa, Eta and Lambda Cassiopeiae. Consequently, the Chinese name for Alpha Cassiopeiae itself is 王良四.
Visibility
With a declination of 56° 32' North, α Cassiopeiae is principally visible in the northern hemisphere. The star is detectable to most observers across the globe reaching as far south as Perth, Australia, Santiago, Chile and other settlements north ± 33° South latitude, albeit close to the horizon. α Cassiopeiae is located in line-of-sight of the Milky Way galaxy, so there are other notable celestial objects one can view close to this star—the Pacman Nebula, NGC 436 and NGC 457 being a few. Alpha Cas reaches its zenith above cities like Edinburgh, Copenhagen and Moscow. It is circumpolar throughout Europe, Russia, and as far south as Los Angeles, California on the North American continent as well as other locations around the globe having a latitude greater than ± 33° North. Since α Cassiopeiae is listed as a second magnitude star, it is easily observable to the naked eye as long as one's stargazing is not hindered by the light pollution common to most cities. The best time for observation is during the late autumn months of the northern hemisphere, when Cassiopeia passes the meridian at midnight, but given its circumpolar nature in many northern localities, it is visible to many of the world's inhabitants throughout the year.
Photometric variations
Depending on the photometric system used, α Cassiopeiae's apparent magnitude is marginally brighter or dimmer than β Cassiopeiae. The Johnson UBV system throughout the latter half of the twentieth century indicated a visual magnitude that ranged from about 2.20 to 2.23, thus making it slightly brighter than Caph with its variable magnitude ranging from 2.25 to 2.31. However recent calculations in the optical V band between 500–600 nanometers by Floor Van Leeuwen in 2007 produced a new measurement for both stars, 2.4107 for α Cassiopeiae and 2.3579 for β, suggesting that β Cassiopeiae ranks as the brightest in the constellation. The confusion arises because of the use of different passbands.
α Cassiopeiae is a red giant star whose spectral classification in the SIMBAD astronomical database is listed as K0IIIa, a stellar class that is notably cooler than the Sun. However, because it is nearing the final stages of its evolution, the photosphere has expanded substantially, yielding a bolometricluminosity that is approximately According to Hipparcos, the New Reduction, the estimated distance to the star is about 70 parsecs or 228 light years. Like all giant stars, α Cassiopeiae rotates slowly with an approximate velocity of 21 km/s—a speed which takes the star approximately 102 days to make one complete revolution on its axis. showing α Cassiopeiae near the heart of the celestial Queen α Cassiopeiae 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. α Cassiopeiae is thought to be around 100 to 200 million years old, having spent much of its time as a blue-white B-type main-sequence star.
Depiction
In 1551, Gerardus Mercator, a Flemishcartographer, produced a celestial globe portraying the 48 traditional Ptolemaic constellations in addition to two others, Coma Berenices and Antinous. On this globe, he represents Cassiopeia as the Queen of Ethiopia, punished for her boasting by being chained to a chair hanging upside-down. α Cassiopeiae is found near her left breast, reflecting its Arabic etymological origin.
