Castor B
star · Gemini · 2.9ᵐ
White star in Gemini. It lies about 52 light years from Earth. In visible light it shines roughly 15 times as bright as the Sun.
Notable facts
The light you see today left Castor B around the year 1974.
About 18 times brighter than the faintest star visible to the naked eye.
In brief
Which constellation is Castor B in?
Castor B lies in Gemini.
Is Castor B visible to the naked eye?
2.9ᵐ — visible to the naked eye (under dark skies).
When is the best time to observe Castor B?
Best observed in January.
Data
- RA / Dec (J2000)
- 7h 35m · +31° 53′
- Type
- star
- Constellation
- Gemini
- How to observe
- 2.9ᵐ — visible to the naked eye (under dark skies)
- Spectral class
- A m — white star
- Absolute magnitude
- 1.9ᵐ
- Luminosity (visual)
- ≈15 × the Sun
- Distance
- ~52 light years
Observing tip
Stars stay points at any magnification: aim your telescope for colour, brightness and companions, not detail.
Altitude above the horizon by latitude
| Latitude | Maximum altitude | Rise azimuth |
|---|---|---|
| +60° | 62° · never sets | — |
| +55° | 67° | 23° |
| +45° | 77° | 42° |
| +30° | 88° | 52° |
| 0° | 58° | 58° |
| −35° | 23° | 50° |
Geometric altitude at upper culmination, atmospheric refraction not included. Positive latitudes are in the northern hemisphere.
Culmination time by month
| Month | Culmination |
|---|---|
| January | 23:49 |
| February | 21:42 |
| March | 19:56 |
| April | 18:03 |
| May | 16:09 |
| June | 14:03 |
| July | 11:59 |
| August | 09:58 |
| September | 08:05 |
| October | 06:16 |
| November | 04:15 |
| December | 02:07 |
Upper culmination in local solar time — no time-zone or daylight-saving correction applied.