Castor
Blue-white six-star system · Alpha Geminorum
A single point of light that is actually six stars
Castor looks like one star to the eye but is really a gravitationally bound system of six stars arranged as three close pairs. It is the second-brightest star in Gemini, marking one of the Twins' heads, and is slightly fainter than its golden neighbor Pollux.
Also on: The brightest stars in the night sky · Named stars, A to Z · The hottest stars · Stars in Gemini
Illustration generated from temperature, not a photograph
2.1 ☉
mass (the Sun = 1)
9,900 K
surface · white star
2 R☉
radius (the Sun = 1)
49 ly
from Earth
1.6
apparent magnitude
Visible to the naked eyeno equipment needed · apparent magnitude 1.6
Its light has been travelling 49 years to reach us, so you see Castor as it was 49 years ago.
It lives in
Milky Way
Barred spiral galaxy.
Other notable stars in the Milky Way
Eta CarinaeLuminous blue variableAlnilamBlue supergiantVY Canis MajorisRed hypergiantAlnitakHot blue supergiantDenebBlue-white supergiantMintakaHot blue giant multiple star
Worlds in the same direction on the sky→