The Constellation Gemini
In the sky this month, you’ll see a fine hexagon of bright stars that includes Capella (in Auriga), Aldebaran (in Taurus), Rigel (in Orion), Sirius (in Canis Major), Procyon (in Canis Minor), and the pair of bright stars Castor and Pollux in the constellation Gemini. Today, let’s have a quick look at Gemini, a long graceful constellation representing celestial twins with their feet dipped in the icy stream of the winter Milky Way…
In mythology, the twins were sons of Zeus named Castor and Pollux, who together were known as the Dioscuri. Pollux was a boxer, and Castor a horseman and fierce warrior.
The brothers proved their courage by joining Jason and his Argonauts on his quest for the Golden Fleece, among other adventures. Upon returning, Castor and Pollux met their fate during more sordid matters, falling into a murderous grievance with another pair of twins, Idas and Lynceus over rustled cattle. Castor was killed by Lynceus, who was in turn slain by Pollux.
Pollux grieved for his fallen brother and asked Zeus if the two could share immortality. It pays to have a powerful father: Zeus placed both in the sky as the constellation Gemini. The brightest stars of the constellation take the names of the twins.
The constellation Gemini is easy enough to find, and is most prominent in the evening sky from January through April. It’s lodged between faint Cancer and brighter Taurus, just north and east of the bright red star Betelguese in Orion. Castor and Pollux mark the heads of the twins, and two lines of stars mark their bodies.
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The constellation Gemini, northeast of Orion (click to enlarge)
Along with Taurus, Gemini is the most northerly of the 12 constellations of the zodiac. But it’s still visible to southern-hemisphere stargazers above the northern horizon.
We’ve met blue-white Castor before. It’s a lovely double star in a small telescope. More detailed astronomical measurements reveal Castor as a 6-star system. Yellow-orange Pollux makes a lovely colour contrast with Castor.
Gemini makes for pleasant viewing with binoculars. The region around Castor and Pollux are fairly sparse of background stars. But you’ll find a richer star field towards the feet of the twins, which is a particularly splendid region in binoculars, especially around the stars Tejat, Propus, and Mebsuta.
Surprisingly, there aren’t many deep-sky sights in Gemini for backyard stargazers. There are two exceptions: the Eskimo or Clown Nebula (NGC 2392), and the dazzling open star cluster M35, which is not far from the position of the June solstice just over the border in Taurus.
