Alpheratz is the hot blue-white star where two figures meet: the head of Andromeda and the north-eastern corner of the Great Square of Pegasus.
At a glance
| type | blue-white star (class B) |
|---|---|
| distance from the Sun | 97 light-years (29.7 pc) |
| its light left it | 97 years ago |
| luminosity | 173 × the Sun |
| radius | 3.83 × the Sun |
| surface temperature | 10,700 K |
| constellation | Pegasus (Winged Horse) |
Read off the piece’s own catalogue, the same values it draws with.
About Alpheratz
Alpheratz is a blue-white star of class B, hotter and far more luminous than the Sun. Its spectrum is unusual: the light shows strong traces of mercury and manganese, a chemical peculiarity that comes from elements sorting themselves in a calm, slowly mixing atmosphere rather than from what the star is made of overall. It is also a close binary, its companion detected only through the shifting lines in its spectrum.
The name comes from the Arabic for the navel of the horse, from a time when the star was counted in Pegasus. The official constellation boundaries now place it in Andromeda, where it is the brightest star, but sky-watchers still use it as the fourth corner of the Great Square, the large box of stars that dominates the autumn sky in the northern hemisphere. It is one of the stars listed for celestial navigation.
What you see in the piece
From Earth the Great Square looks like a flat box of nearly equal stars. Fly out to Alpheratz and the corners separate in depth, because the four stars lie at very different distances from the Sun.
Questions
Is Alpheratz in Pegasus or Andromeda?
Officially it is the brightest star of Andromeda, but it also forms the north-eastern corner of the Great Square of Pegasus, and older catalogues counted it in both figures.
How far away is Alpheratz?
Alpheratz is 97 light-years (29.7 pc) from the Sun, so the light you see left it 97 years ago.