Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
A Bayer letter is a Greek letter assigned to stars within a constellation based on their apparent brightness. The system was introduced by Johann Bayer in his 1603 star atlas Uranometria.
5 Must Know Facts For Your Next Test
Bayer letters are ordered from the brightest to dimmest stars using the Greek alphabet (α, β, γ, etc.).
The brightest star in a constellation is typically designated as Alpha (α).
In cases where there are more than 24 stars, Latin letters or numbers may be used after the Greek alphabet.
Bayer’s naming convention helps astronomers easily identify and categorize stars within constellations.
The Bayer designation of a star includes both its Greek letter and the genitive form of its constellation name (e.g., α Centauri).
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Related terms
Constellation: A group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure.