Alpheratz — Star in Andromeda
HIP 677; Alpha Andromedae; 21 Andromedae
About Alpheratz
Description
Alpheratz is a blue-white star of spectral type B8IVpMnHg at magnitude 2.06, shared between Andromeda and Pegasus — it marks both the head of Andromeda and the northeast corner of the Great Square of Pegasus. Located about 97 light-years from Earth, it is a chemically peculiar star with unusually high concentrations of manganese and mercury in its atmosphere.
Observing Tips
Alpheratz is easy to find as the upper-left (northeastern) corner of the Great Square of Pegasus in autumn skies. It connects the Square to the chains of stars forming Andromeda. From Alpheratz, follow the upper chain of Andromeda stars to find M31, the Andromeda Galaxy. Best observed September through January.
History
The name Alpheratz comes from the Arabic 'surrat al-faras,' meaning 'the navel of the horse,' from when it was considered part of Pegasus. It was officially assigned to Andromeda as Alpha Andromedae in 1930 by the IAU, though it still visually belongs to both asterisms.
Fun Facts
Alpheratz is the brightest known mercury-manganese star — a type of chemically peculiar star where atomic diffusion causes certain heavy elements to concentrate in the stellar atmosphere. Its manganese abundance is about 200 times solar.
Observe
1Physical Properties
2Position & Identifiers
3How easy to spot?
| Equipment | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| Naked eye Naked eye | Easy | Easy | Easy |
| 50 mm finder 50mm finder | Easy | Easy | Easy |
| 150 mm telescope 150mm scope | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Survey Image
Loading survey image…
Explore
7
Size Comparison
8
Compare Stars
9
Spectral Classification
10
Hertzsprung-Russell Diagram
11
Stellar Lifecycle
12
Blackbody Spectrum
13
Stellar Absorption Spectrum
Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.
14
Stellar Fusion
Discover
15Stellar Notes
16
Light Travel Time Machine
17
Relativistic Travel
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
Explore Nightbase
Related knowledge, tools, and stories — no observation planning required.
