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Here's a quote from the "National Audubon Society - Field guide to the Night Sky"
Quote
"Gemini
alpha is Castor, second brightest star of Gemini. To the unaided eye Castor appears a a single star of spectral type A1 V and magnitude 1.6, but it is actually a sextuple. Through a telescope it looks like two stars of magnitudes 2 and 3, only 2" apart, with a 9th magnitude companion 73" from them. Each of these three stars is itself double. The system of stars is 46 ly from Earth."
End Quote.
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