Castor: how to find it and when to see it
Castor ranks 23rd of the 74 bright stars on our list, at magnitude 1.58, in the constellation Gemini.
You can see it from anywhere north of 58° S, and it's highest in the evening sky in February.
Castor at a glance
- Constellation
- Gemini
- Magnitude
- 1.58
- Rank on our list
- 23 of 74
- Hemisphere
- Northern
- Right ascension
- 7 h 35 min
- Declination
- 31.9° north
- Visible from
- north of 58° S
- Never sets
- north of 58° N
- Best evening
- 28 February
- Name from
- Greek
Where Castor is in the sky
Castor sits 31.9° north of the celestial equator, the line in the sky directly above Earth's equator, so it's in the northern half of the sky. Its right ascension is 7 h 35 min.
Right ascension works like longitude on the sky. It's counted in hours, and about one hour of it turns past you each hour of the night.
When and where to see Castor
From the northern hemisphere
From 40° N, the latitude of New York, Madrid and Beijing, Castor rises in the north-east, climbs to 82° above the horizon in the south and sets in the north-west.
It's in the evening sky from November to May, and it's highest in the evening around 28 February, in winter.
From the southern hemisphere
From 34° S, the latitude of Sydney, Cape Town and Buenos Aires, Castor rises in the north-east, climbs to 24° above the horizon in the north and sets in the north-west.
It's in the evening sky from January to April, and it's highest in the evening around 28 February, in summer.
How high Castor climbs from each latitude
The evening is about 9 pm local time, or 10 pm in summer time, and later when the sky is still too bright. A star counts as in the evening sky when it's at least 10° above the horizon.
| Latitude | Visibility | Highest point | Evening sky |
|---|---|---|---|
| 60° N | Never sets | 62° in the south | Nov to May |
| 50° N | Rises and sets | 72° in the south | Nov to Jun |
| 40° N | Rises and sets | 82° in the south | Nov to May |
| 30° N | Rises and sets | 88° in the north | Dec to May |
| 20° N | Rises and sets | 78° in the north | Dec to May |
| Equator | Rises and sets | 58° in the north | Dec to May |
| 20° S | Rises and sets | 38° in the north | Jan to Apr |
| 34° S | Rises and sets | 24° in the north | Jan to Apr |
| 45° S | Rises and sets | 13° in the north | Feb to Mar |
What the name Castor means
Castor is named after one of the twin brothers of Greek myth that Gemini shows. His twin, Pollux, is the brighter star beside him.
Keep the sky of a night that matters
Our star maps show the stars above any place, at the minute you choose, with the constellation lines drawn in. If Castor was above the horizon that night, it's on your map, and we print it on museum-grade paper.
Questions about Castor
Castor is in Gemini. It sits 31.9° north of the celestial equator, at a right ascension of 7 h 35 min.
Castor is highest in the evening sky around 28 February. That's winter in the northern hemisphere and summer in the southern hemisphere.
Yes, from anywhere north of 58° S. From 34° S, it climbs to 24° above the horizon in the north.
Castor has a magnitude of 1.58, which ranks it 23rd of the 74 bright stars on our list. Sirius looks about 16 times brighter.
Castor is named after one of the twin brothers of Greek myth that Gemini shows. His twin, Pollux, is the brighter star beside him.