Gemini? Here’s your constellation

The constellation Gemini, with its two brightest stars, Castor and Pollux, shines prominently in winter and spring night skies of the Northern Hemisphere.

Antique colored etching showing stars in Gemini superimposed on a painting of two young brothers.

This depiction of the Gemini twins is from Urania’s Mirror, a set of cards containing astronomical star charts, first published in 1824. Image via Wikipedia.

Most people see the constellation Gemini as just two bright stars – Castor and Pollux – sometimes called the Gemini twins. These two stars aren’t really twins. Pollux is brighter and more golden in color. Castor is slightly fainter and white. But both stars are bright, and they’re noticeable for being close together on the sky’s dome. From time immemorial, people have thought they looked like brother stars.

Two bright stars against a star field. Pollux appears as a light gold star while Castor appears blue-white.

A photo of Castor and Pollux showing their color differences. Image via Rogelio Bernal Andreo/ RBA Premium Astrophotography.

January, February and March are great for observing these stars. Then Gemini is well up in the east at nightfall. In early February, Gemini climbs highest in the sky around 10 p.m. local time. In late February, the constellation is highest around 9 p.m. That’s local time, the time on your clock, no matter where you live around the globe.

Gemini stays in view in the evening sky until around May. By late May and June, Gemini is found low in the west at nightfall, and Gemini’s two brightest stars – Castor and Pollux – fade into the sunset before the June 21 summer solstice. The sun annually passes in front of Gemini from about June 21 until July 20.

In skylore, Castor and Pollux were the sons of a mortal mother, Leda. Castor was the mortal brother, son of Tyndareus, and Pollux the immortal brother, son of Zeus. Castor and Pollux were joyfully united in spirit, yet sorrowfully divided by circumstance. When Castor was slain in battle, Pollux was inconsolable and begged Zeus to relieve him of the bonds of immortality. Zeus granted his request, and, to this day, Pollux and Castor stand reunited in the heavens, a tribute to the redemptive power of brotherly love.

Thus the Greek myth of Castor and Pollux explores the inherit duality of life, of mortality and immortality forever intertwined.

A star map of Gemini.

The two bright stars Castor and Pollux each mark a starry eye of a Gemini Twin. If you have binoculars and a dark sky, be sure to check out Gemini’s beautiful star cluster, Messier 35, or M35, in western Gemini near the Taurus border. See it, at the foot of Castor? Image via AugPi/ Wikimedia Commons.

Here’s how to find Gemini from the constellation Orion. If you pick out any noticeable sky pattern in the February night sky, that pattern has a good chance of being the constellation Orion the Hunter. On February evenings, from the Northern Hemisphere, Orion is high in the south.

Orion is noticeable for its Belt stars, a short, straight row of three medium-bright stars. Look below Orion’s Belt for the very bright blue-white star Rigel. See it? Now look above Orion’s Belt for the reddish star Betelgeuse. See that? You can draw an imaginary line from Rigel through Betelgeuse to locate Castor and Pollux. Remember, you’ll be looking for two bright stars that are noticeably close together.

A star map showing Orion and Gemini, with a line from Rigel to Betelgeuse pointing towards Castor and Pollux.

Facing south to southwest (from Northern Hemisphere locations) on January, February and March evenings. Draw an imaginary line from Orion’s 2 bright stars – Rigel through Betelgeuse – to star-hop to Castor and Pollux. For a specific location and time of year, try Stellarium.

Here’s how to find Gemini using the Big Dipper. The Big Dipper is an asterism, not a true constellation, but just a very clear dipper-shaped pattern of stars. The Big Dipper is always located generally northward on the sky’s dome. Draw an imaginary line diagonally through the bowl of the Big Dipper, from the star Megrez through the star Merak. You are going in the direction opposite of the Big Dipper handle. This line will point to Castor and Pollux.

A star map showing Gemini and the Big Dipper, with a line from two stars in the Big Dipper bowl pointing to Castor and Pollux.

Facing (from Northern Hemisphere locations) on late evenings in January and February, and evenings in March. Draw an imaginary line diagonally through the Big Dipper bowl to locate Castor and Pollux. For a specific location and time of year, try Stellarium.

You can also use the moon to find Gemini. As the moon swings full circle through the constellations of the zodiac, it passes through Gemini for a few days each month. Check EarthSky Tonight – especially in the months of January, February and March – for posts showing you the moon near Castor and Pollux on specific dates. It’ll happen next around March 5, 2020.

Or play around with the online planetarium program, Stellarium. It can show you when the moon moves through Gemini every month (except during those months when Gemini is behind the sun).

Star chart showing ecliptic and moon near Gemini stars.

The moon will pass near Castor and Pollux next around March 5, 2020. Read more.

By the way, Gemini and nighttime’s brightest star, Sirius, reach their highest points in the sky at roughly the same time. At middle latitudes in the Northern Hemisphere, we see Gemini’s brightest stars, Castor and Pollux, nearly overhead while Sirius sparkles quite low in our southern sky. South of the equator, it’s the opposite: Sirius shines way up high while Gemini sits low in the northern sky.

Red Greek vase painted with black silhouetted images of Castor and Pollux with their parents and a horse.

An amphora dating between 540-530 B.C., from Etruria (central Italy), shows Castor and Pollux. Castor, the mortal brother, accepts a flower from his mother, Leda. His father, Tyndareus, is in front of the horse. Pollux, the immortal brother, is at the left of the image with a dog. Image via Egisto Sani/ Flickr.

Bottom line: Winter and spring are the best times to look for the constellation Gemini in the night sky. Castor and Pollux, the two brightest stars in Gemini, are twin brothers from Greek and Roman mythology.

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Bruce McClure