White star · Gemini

Castor B

Also known as: α Geminorum (α Gem)

mag 2.952 light-years

About

Castor B (α Geminorum) is a white star of magnitude 2.9 in Gemini, about 52 light-years away.

Castor B is in the constellation Gemini.
Best evenings: around late February it is highest at about 9 pm (10 pm in summer time); a month earlier, two hours later.
Where on Earth: it is seen well, at least 10° up, from north of 48° S.

When it rises and sets tonight, how high it climbs and how much the Moon gets in the way are worked out in your browser for your place.

EyesEasy, even from town.
Binoculars (10×50)A sharp point; binoculars bring out its colour and the fainter stars around it.
Telescope (6–8 inch)Still a point of light at any magnification — stars are too far away to show a disc. Low in the sky, bright stars twinkle and flash colours.

Stars look the same in any instrument: brighter and sharper, but never bigger.

Proper name	Castor B
Designation	α Geminorum (α Gem)
Type	White star
Spectral type	A m
Magnitude	2.9The smaller the number, the brighter.
Distance	52 light-yearsThe light you see left it around 1974.
Proper motion	0.19″ per year across the sky
Constellation	Gemini
Right ascension (J2000)	07h 34m 36.6s
Declination (J2000)	+31° 53′ 26″