Castor (alpha Geminorum) is a bright star system consists of six individual starts in the constellation of Gemini.

Castor is a binary, period about 500 years, half large axis of the ellipse 105 Astronomical Unit.

Both components are spectroscopic binary itself with periods of 9 and 3 days. At a distance of 100 A.E. of the visual binary is a small third component (M1 spectrum, magnitude 9.1), which themselves cover a variable with a period of 0.8 day. All Castor system consists of six individual stars.

The representatives of Castor of Castor Castor B and C. The supervisor, Castor B is also a spectroscopic binary. The supervisor runs in three days to around Castor B. In fact a sixfold system. There is also a red dwarf, Castor C slowly around Castor A and Castor B runs. The star is also variable in is also known as YY Gem.

Delta Geminorum. This is a beautiful white, his supervisor is a lot weaker. The orange dwarf than with a small telescope is very difficult to recognize. The stars are bright units of magnitude 3.5 and 8.2. They are 5.8 apart.

The Eta Geminorum. It is a visual binary only in larger telescopes is the separation. The companion is magnitude 8.8.