Have You Met the Twins?

Of course, I’m referring to Castor and Pollux, who, according to Greek mythology, were twin brothers. Their mother was the Spartan Queen, Leda; Castor was the son of Tyndareus, the king of Sparta, and Pollux the divine son of Zeus. I’ll let you do the research yourself to discover how that came about. Castor and Pollux have also been associated with St. Elmo’s fire. Here they played the role of protectors of sailors. It’s to my understanding that Castor was a mortal (like the rest of us) and when he died, Pollux begged his father Zeus to give Castor immortality, which he did, by uniting them together in the heavens. Therefore, giving us mortals here on Earth the constellation known as Gemini, which in Latin means “the twins”.

The constellation Gemini rides along the Ecliptic and is nearly centered on the local Meridian at 02:20 UT for mid-northern latitudes. This is a perfect time to view Gemini’s deep sky targets with a small telescope. Gemini is home to open clusters, double stars and planetary nebula of which a few are visible in telescopes of 80mm.

The Twins

Our first target is the double star Castor which, although it carries the Bayer designation “Alpha”, is the second brightest star in Gemini. This showpiece double is one of the finest double stars visible in the northern hemisphere. In the 90mm f/10 refractor, Castor is easily split at 101x. Both stars appear white with a separation of about 4.2” in PA 62°. An interesting note about Castor is that it is really a sextuplet star. Larger telescopes may show a 9.8 magnitude companion about 71” from the main pair and each of these stars is a spectroscopic binary. Let’s take a look at the other twin, Pollux. There are a few references to Pollux being a double star however, according to Robert Burnham, Jr. (1931-1993); none of the faint visual companions to Pollux listed in the Aitkin’s Double Star (ADS) Catalogue are gravitationally bound. Nevertheless, Pollux is an interesting star indeed. Pollux is an orange giant star with the classification of K0III. This luminary shines at magnitude 1.15 and is about 33 light-years distant. This star boasts twice the Sun’s mass and almost ten times the solar radius. But, Pollux real claim to fame is its extrasolar planet with a mass almost 2.5 times that of Jupiter. The planet, Pollux b, has an orbital period of 590 days.

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