Gemini - Pollux and Castor - Stars and Myths
I’ve always been fascinated by the constellations. I learned about them in detail in middle school and I still enjoy taking out my star maps to locate them in the sky.
One constellation, Gemini, is particularly interesting to me. I was born right when the sun entered Gemini – supposedly – and it’s an easy-to-identify constellation in the sky.
Gemini is one of the constellations of the zodiac.
The zodiac includes 12 constellations that are located around the ecliptic (basically a celestial sphere) and include Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Capricorn, Sagittarius, Aquarius and Pisces.
Pollux & Castor
A few ancient tales exist about Gemini. Its name means “twins.” Since the dawn of humans, civilizations have given Gemini various “twin” names. Arabs in the Middle East called it Two Peacocks, the Hindus named it Twin Deities and the ancient Egyptians heralded it as Two Sprouting Plants.
The two brightest stars in Gemini are called Pollux and Castor.
One story says that Pollux and Castor were the twin sons of the Queen of Sparta, named Leda. Jupiter was their father. Jupiter may not have been Castor’s father, though, because Castor was mortal and Pollux was not.
When Castor died in battle, Pollux begged for his brother’s immortality. It was granted, but they both had to move to the sky.
Another tale recounts how the brothers joined the Argonauts, a group of mariners trying to secure the Golden Fleece. Jason, their leader needed to find the fleece to secure his place on the throne.
Castor had a penchant for horses and Pollux was a brave fighter, often only fighting with his bare hands.
In ancient times, mariners on the sea wanted to honor Leda when they saw a curious glow around the ropes during lightning storms. They called them Ledean Lights.
In January, the constellation Gemini is in the eastern sky by dusk. In June, it’s in the western sky. It’s located in the Northern Hemisphere.
The constellation is characterized by two relatively bright stars. Pollux and Castor are the “heads” and their bodies extend virtually parallel down from them. The northern “feet” are closer to the constellation Taurus and the southern “feet” are nearer to Orion.
If you look closely, you may be able to see showers of meteors around the feet of the constellation in mid-October and around the head in early to mid-December.
The entire constellation of Gemini boasts more than 50 double-stars. They can only be seen with a telescope.
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Pollux is brighter than Castor. That wasn’t always the case, though. Castor used to be brighter a long time ago. It’s the largest double star in the northern hemisphere. This double star was the first of its kind for scientists to discover.
Castor is pretty bright, as well. It’s magnitude (measure of brightness) is between 1.9 and 2.9. On a scale of 0-5, 0 is considered the brightest object, and 5 is the least bright. It’s about 47 light years away.
Castor as a double star can be seen with a small telescope, but it’s not visible to the naked eye. The two stars revolve around each other every 420 years.
Pollux is brighter at a magnitude of 1.2, making it the 15th brightest star in the northern sky. It’s located about 31 light years away, but retreating at a rate of 2 miles per second!
Gemini’s stars have a name designation called Geminorum. Castor is α Geminorum; β Geminorum is Pollux.
Sir William Herschel was studying the constellation in 1781 when he saw an unidentified object near the star η Geminorum, also called Propus.
Six months later, he determined that it was a planet – not a comet – and one that was twice as far from the sun as its planetary neighbor, Saturn.
The scientific community finally decided to name this new planet Uranus. Saturn’s mythical father was Uranus.
Near the star δ Geminorum (also called Wasat) is where the planet Pluto was discovered in 1930.
Not visible to the naked eye, but interesting nonetheless is the star cluster M35. It’s located at Castor’s feet, right by 1 Geminorum. Astronomers call it one of the most beautiful objects in the sky.
This is just one constellation of which to study, but is incredibly interesting.
References and Resources
Field Book of the Skies. Olcott, William T. G.P. Putnam's Sons, New York: 1954.
The Handy Space Answer Book. Engelbert, Philis and Diane Dupuis. Visible Ink Press, MI:1998.
Guide to Stars and Planets. Moore, Sir Patrick. Firefly Books, New York: 2005.
© 2012 Cynthia Calhoun