Castor (α Gem)

Castor (α Gem) is a double star in the constellation Gemini, magnitude 1.9.

A bright, close pair in Gemini; Castor is a sextuple system in which A and B are spectroscopic binaries and faint Castor C is an eclipsing pair. Its components (magnitudes 1.9 and 3.0; spectral types A1 V (white) and A4 V (white)) lie 5.77″ apart at PA 49° (predicted for 2027.0 from its 459-year orbit). Castor C (magnitude 9.8) lies 69.6″ away.

When and where to see it

It is best placed in the evening sky around February, when it crosses the meridian at about 10 pm local time (around midnight in January). It can be seen from everywhere north of 58°S and never sets north of 58°N.

At its highest it stands 72° up from 50°N, 87° up from 35°N, 58° up from the equator, 23° up from 35°S.

Facts

Type

Double star

Constellation

Gemini

Designations

α Gem, Alpha Geminorum, 66 Gem, 66 Geminorum, STF 1110, HIP 36850

Magnitude

1.9

Position

RA 7h 34.6m, Dec +31° 53′ (J2000)

Open AstroPilot to see when Castor (α Gem) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.