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Alpheratz

Sirrah, Alpha Andromedae, 21 Andromedae, Delta Pegasi

Proper NamesAlpheratz, Sirrah
Bayer DesignationAlpha Andromedae
Flamsteed Number21 Andromedae
BSC15
HD358
ConstellationAndromeda
Right Ascension0h 9m 27s
Declination+29° 12' 20"
Distance97 light years
30 parsecs
MagnitudeApparent: +2.1
Absolute: -0.3
Spectral ClassB4IV:pHgMn Blue Subgiant
Optimum VisibilityOctober
NotesAlpheratz is a spectroscopic binary system whose main subgiant star is categorised a variable. In fact, it has shown little evidence of this variability over recent years, but any historical variability is thought to be related to its unusually high levels of mercury, which is unevenly distributed across the star's surface.

A second magnitude star that belongs to both the constellation of Andromeda and the Square of Pegasus. Its brightness is somewhat variable: Alpheratz' luminosity varies as it turns on its axis. It has a companion star, much fainter than the main blue star we see from Earth.

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