Star · A2V
Castor
Castor is a main-sequence star of spectral type A2V in the constellation Gemini, 50.9 light-years from the Sun.
| Other names | α Gem · Gl 278A · HIP 36850 |
|---|---|
| Constellation | Gemini |
| Distance | 50.9 light-years (15.6 pc) |
| Apparent magnitude | magnitude 1.58 |
| Absolute magnitude | magnitude 0.61 |
| Spectral type | A2V |
| Surface temperature | 9,720 K |
| Luminosity | 64 L☉ |
| Radius | 2.82 R☉ |
| Mass | 2.98 M☉ (estimated) |
| Right ascension (J2000) | 7h 34m 35.9s |
| Declination (J2000) | +31° 53′ 18″ |
| Space velocity (relative to the Sun) | 21.9 km/s |
In the sky
Visible to the naked eye under a dark sky (apparent magnitude 1.58). Visible from the whole Northern Hemisphere and south to latitude 58° S. North of latitude 58° N it never sets. It stands highest at midnight in January, the best time to observe it.
Through a telescope from Earth
Light's journey
The light you see tonight set out around the year 1975. At the speed of Voyager 1, the fastest craft leaving the Solar System (16.9 km per second), the trip would take 902 thousand years.
The Sun seen from there
From a planet around Castor, the Sun would look like a star of magnitude 5.80, in the direction where our sky has the constellation Sagittarius. It would be visible to the naked eye.
Neighbours
Its nearest neighbours in the catalogue (within 20 light-years):
- Castor B 0.68 light-years
- Gl 278C 1.68 light-years
- GJ 1096 3.72 light-years
- WISE J072312.44+340313.5 3.94 light-years
- WISEPA J075003.84+272544.8 5.63 light-years
- Gl 295 7.53 light-years
- ρ Gem 8.07 light-years
- HIP 36357 8.31 light-years
Position, brightness and colour from the HYG / AT-HYG catalogue; temperature, luminosity, radius and mass are approximate values computed from these observations.