Celestial News: March belongs to the Gemini constellation
For Steamboat Pilot & Today
Only four of the 88 constellations in our sky contain more than one of the 25 brightest stars.
These would be Orion (Rigel and Betelgeuse), Centaurus (Rigel Kentaurus and Hadar), Crux (Acrux, Mimosa and Gacrux) and Gemini (Pollux and Castor). Of these, only Orion and Gemini are visible from mid-northern latitudes. If February is the prime month to view Orion in the early evening, then March belongs to Gemini.
Step outside around 8:30 p.m. on any March evening and look straight up toward the zenith. There you can’t miss Gemini’s twin stars, Pollux and Castor.
The Gemini twins are positioned in the sky standing over the great hunter Orion, as he fights off Taurus the Bull. The stars Pollux and Castor represent the heads of the famous twins and the fainter stars Propus and Alhena mark their feet.
Gemini is one of the 12 constellations of the zodiac, which means that it lies along the path that the sun, moon and planets follow in their journeys around the sky. The sun’s northernmost position lies right at the feet of the Gemini twins, near the beautiful star cluster M35.
Pollux and Castor were fraternal twins born to Leda. The ancient Greeks called them the Dioscuri, or sons of Zeus, although only one of the mythological twins was said to be fathered by the king of the gods.
Castor’s father was Leda’s actual husband, Tyndareus, while Pollux’s father was Zeus. Thus, Pollux was immortal like his father, but his brother Castor was a mere mortal.
Although they weren’t conjoined twins, they were inseparable, nonetheless. The two brothers were also very close to their two sisters, Helen (of Troy) and Clytemnestra. Pollux and Castor shared many adventures in Greek mythology, even sailing with Jason and the Argonauts in their quest for the Golden Fleece.
The Gemini twins were thought to bring good luck to sailors, sometimes appearing as a bright blue glow atop the ship’s mast. St. Elmo’s fire, as it is now known, is caused by a static electrical build up on a pointy object, like a mast, during a thunderstorm.
When Castor was mortally wounded in battle, Pollux pleaded with Zeus to grant his brother immortality, too, that he should not die. Zeus heard the plea and immortalized both brothers in the sky, side by side forever, as our constellation of Gemini, the Twins.
Close inspection reveals that the star Pollux, representing the immortal twin, is slightly brighter than Castor, the mortal twin. That’s how I remember which one is which.
Aim a medium-sized telescope at Castor and you might think that you are seeing double. In fact, you are. Castor is a fine example of a binary star, two stars that appear as one to the naked eye.
Each of these stars is again double and are circled by yet a third pair of faint stars, making Castor a rare sextuple star system, about 51 light years from Earth. Pollux is a little closer to us, at 33 light years, and has no known stellar companions.
Recent studies, however, show that Pollux has at least one large planet orbiting around it. This planet, formally named Thestius, is more than twice the size of our solar system’s largest world, Jupiter.
The beautiful star cluster at the twins’ feet is called Messier 35, or M35 for short. M35 is estimated to be 175-million years old — fairly young for a star cluster. It contains over 400 stars and covers an area of the sky equivalent to the full moon.
Although M35 is visible to the unaided eye as a fuzzy smudge, binoculars or a small telescope are needed to show its twinkling stars. M35 is 3870 light years from earth. A much more distant star cluster, NGC 2158, appears at the edge of M35.
The Geminid meteor shower springs out of this constellation in mid-December every year, from a point near the star Castor. Up to 90 meteors per hour can be seen on the night of the peak, making it one of the best of our annual meteor showers.
NASA’s Gemini Program in the 1960s was named for the celestial twins because each Gemini mission launched two astronauts toward the stars.
For information about astronomy-related events in Steamboat Springs, including public star parties at CMC’s Ball Observatory, contact physics and astronomy instructor Paul McCudden, at firstname.lastname@example.org or 970-870-4537 or visit the SKY Club web page at http://www.coloradomtn.edu/skyclub.
Jimmy Westlake is adjunct Professor of Physical Sciences at Colorado Mountain College and former Director of the Rollins Planetarium at Young Harris College in Georgia and the St. Charles Parish Library Planetarium, in Luling, Louisiana. His “Celestial News” column appears monthly in the Steamboat Today newspaper. Check out Jimmy’s astrophotography website at http://www.jwestlake.com.
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