Castor B
star · Gemini · 2.9ᵐ
White star in Gemini.
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
- ≈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.