Cepheus

Lore & Background

Cepheus was the King of Aethiopia. He was married to Cassiopeia and was the father of Andromeda, both of whom are immortalized as modern day constellations along with Cepheus. In visualizations, Cepheus is most commonly depicted as holding his arms aloft, praying for the deities to spare the life of Andromeda, or as a more regal monarch sitting on his throne.

Reader's Guide

Cepheus is significant in astronomy for several reasons. Its brightest star, Alderamin (Alpha Cephei), has an apparent magnitude of 2.5. The constellation contains multiple red supergiants—Mu Cephei (the Garnet Star), VV Cephei A, Zeta Cephei, and V381 Cephei Aa—among the largest stars known, all accepted core-collapse supernova candidates.

Did You Know?

• Delta Cephei is the prototype of the Cepheid variable stars, varying between magnitude 3.5 and 4.4 over 5 days and 9 hours.

Common Misconceptions (Editorial)

Some people assume that constellations named after mythological figures are always depicted in a heroic or triumphant pose, but Cepheus is most commonly shown with his arms aloft, praying for his daughter Andromeda's life. Additionally, it is often thought that all variable stars are rare or obscure, but Delta Cephei is the prototype of the famous Cepheid variables and varies predictably between magnitude 3.5 and 4.4 over a well-documented cycle.

Why It Matters (Editorial)

Cepheus endures as a celestial landmark because it bridges ancient storytelling and modern astrophysics, housing both the mythic lineage of a king pleading for his family and some of the most extreme objects in the universe—from ultramassive black holes to the giant stars that gave us the Cepheid variable, a key tool for measuring cosmic distances. Its place among Ptolemy’s original 48 constellations reminds us that our maps of the night sky are woven from both human imagination and scientific discovery.