Schedar (Alpha Cassiopeiae) is a second magnitude star in the constellation Cassiopeia which despite its “Alpha” designation appears to be marginally dimmer than Beta Cassiopeiae (Caph), depending upon which frequency is used to measure Schedar’s brightness. For instance, while measurements made in the optical V-band at 500-600 nanometers show that the star Caph is the brightest in the constellation, new measurements made with the WISE telescope, on the other hand, show that Schedar is in fact the brightest star in the constellation with an absolute magnitude of 2.240, making it 18 times brighter than the absolute magnitude of the star Caph.
• Constellation: Cassiopeia
• Coordinates: RA 00h 40m 30.4405s |Dec. +56° 32′ 14.392″
• Distance to Earth: 228 2 light years
• Star Type: K0IIIa
• Mass: 4 – 5 sol
• Radius: 42.1 sol
• Apparent Magnitude: -1.985
• Luminosity: 676 sol
• Surface Temperature: 4,530K
• Rotational Velocity: 21 km/sec
• Proper motion: RA 50.36 milliarcseconds/year |Dec. -32.17 milliarcseconds/year
• Age: 1–2 hundred million years
• Other Designations: 18 Cas, HR 168, BD+55°139, HD 3712, SAO 21609, FK5 21, HIP 3179, GC 792, ADS 561, CCDM J00405+5632
Although Schedar is best viewed from the northern hemisphere, it is nevertheless visible to observers as far south as about ± 33° South latitude, albeit low on the horizon at locations such as Perth in Australia, and Santiago in Chile. Note also that although Schedar is circumpolar throughout Europe, it is also circumpolar as far south as the city and environs of Los Angeles in California. In terms of naked eye visibility, Schedar is easily visible throughout the year under dark skies from almost anywhere on the globe north of latitude 33° N.
Put simply, there is nothing about the star Schedar that distinguishes it from other red giant stars. The SIMBAD database lists the star as having a stellar classification of K0IIIa, which means that it is significantly cooler than the Sun, but since it is now approaching the end of its red giant phase, the star’s photosphere has expanded greatly to the point where its bolometric luminosity is about 676 times brighter than that of the Sun. Like most other giant stars, Schedar is a slow rotator, completing one revolution every 102 days at a rotational velocity of about 21 km/sec at its equator.
Although Schedar was once thought to be a variable star, no variability has been detected during the last one hundred years or more. Moreover, three faint companions that were once thought to be orbiting Schedar are now thought to be line-of-sight companions that merely lay along the same line of sight as Schedar, although this remains to be demonstrated definitively.
The star’s traditional name “Schedar”, first appeared in the Alfonsine tables published in the 13th century, and according to most authorities, the name derives from the Arabic word “sadr”, meaning“breast”, as a reference to the star’s position in the breast of the mythical queen Cassiopeia in classical depictions of the constellation. However, one other traditional Arabic name includes “Al Dhat al Kursiyy”, which means “[the] lady in the chair”.
In China, the star Schedar forms part of an asterism known as “Wang Liang”, named after a famous charioteer of the Spring and Autumn Period. The asterism is made up of the stars Alpha Cassiopeiae, Beta Cassiopeiae, Kappa Cassiopeiae, Eta Cassiopeiae, and Lambda Cassiopeiae, and due to its position in the asterism, Schedar is known in China as “Wáng Liáng sì”, which means “[the] Fourth Star of Wang Liang”.