Star profile

Castor

Alpha Geminorum · Gemini

3D likeness based on its real data · class A · ~8,500 K

What is Castor

Castor shines in Gemini just 50.9 light-years away, close enough to count as a cosmic neighbour. It is a white class-A star that looks like a single point to the naked eye, though telescopes reveal a tangled stellar family hiding behind it. To the ancient Greeks it stood beside Pollux, the divine twins of Leda, horsemen and patrons of sailors who prayed for clear weather.

Where it is and when to see it

Castor lies in the northern celestial hemisphere. It is visible to the naked eye under a dark sky. Its best month of the year is January, when it culminates around midnight.

From London it culminates about 70° above the horizon.
From New York it culminates about 81° above the horizon.
From Sydney it culminates about 24° above the horizon.

It can be seen from anywhere north of 58° S.

It ranks no. 2 in brightness among the 74 stars of Gemini in our catalogue. To find it, start from Pollux, the brightest: it lies about 5° away (a fist at arm's length covers about 10°).

The light you see today left it about 51 years ago.

Find it on the sky map

It opens in your browser. Free, no account, nothing to install.

Leave your signature on Castor

Your name and a message go up on the map for everyone to read. Signing is free.

Without a lock, someone else can replace your signature. How the lock works

We'll ask for an email to confirm it's you, no password.

Write my signature

A public signature from a real person. The chosen name is a symbolic denomination within Stelvia, with no official standing or IAU recognition: the sky is not for sale and belongs to no one.

Astronomical data for Castor

Constellation: Gemini
Apparent magnitude: 1.58
Distance: 50.9 light years
Coordinates (J2000): RA 113.650° · Dec 31.888°
Catalogue: HIP 36850 · HD 60179

A symbolic commemorative gift: neither the signature nor the chosen name implies ownership of the star or recognition by the IAU.

Other stars in Gemini

Gemini has 74 stars in Stelvia's catalogue. Here are a few of them.

See all 74 stars in Gemini