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Following Castor through the years

Even a small backyard telescope can reveal the orbital motion of a binary star.
Castor-sketches
Glenn Chaple's observations with his 3-inch f/10 reflecting telescope at 120x show the position shift of Castor between 1976 (at left) and 2008 (right).
Glenn Chaple
In my July 2011 column, I wrote about observing visual binaries over a lifetime as they undergo a large portion of their orbits. I’ve followed the orbital shift of a trio of binary stars, including Alpha (α) Geminorum, better known as Castor.

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