Castor vs Pollux
Colour is the plainest difference between them: Castor is an A-type star in Gemini and Pollux a K-type star in Gemini, most of the Harvard sequence apart. Pollux is the intrinsically fainter of the two, its absolute magnitude of +1.08 trailing +0.62 by a margin worth about 1.5 times the light. To the unaided eye Pollux leads at magnitude +1.16 to +1.58, a gap of 0.42 worth about 1.5 times the light of Castor. Pollux is the nearer of the two at 33.8 light-years, while Castor lies 50.9 light-years away, some 1.5 times farther.
Property comparison
| Property | Castor | Pollux |
|---|---|---|
| Designation | 66Alp Gem | 78Bet Gem |
| Constellation | Gemini | Gemini |
| Spectral Class | Class A — A-type (White) | Class K — K-type (Orange) |
| Apparent Magnitude | +1.58 | +1.16 |
| Absolute Magnitude | 0.62 | 1.08 |
| Distance | 50.9 ly | 33.8 ly |
| Mass | N/A | N/A |
| Radius | N/A | N/A |
| Temperature | N/A | N/A |
| Luminosity | N/A | N/A |
Full data for each star: Castor · Pollux
Key differences
Key Differences
- ◆ Both are the 'twin' stars in Gemini and are frequently compared as a pair.
- ◆ Despite being Alpha Geminorum, Castor is actually dimmer than Beta Geminorum (Pollux).
- ◆ Pollux is a K-type giant; Castor is an A-type main-sequence star.
- ◆ Castor is a remarkable sextuple system (6 stars in 3 binary pairs); Pollux is a single star with an exoplanet.
- ◆ Pollux's exoplanet (Thestias) made it the first giant star confirmed to host a planet.