07 - The Heavenly Twins - February 2013

The Heavenly Twins

Shining brightly low to the north-east in February and March around 9pm, about 25 degrees above the horizon, you will find two prominent stars 4.5 degrees (or 9 moon diameters) apart.  They stand out like a pair of sore thumbs. These are the famous Twins of Gemini, one of the zodiac constellations. 

They are better known as Castor and Pollux, the twin members of the famous Argonauts in Greek mythology.  Pollux is the brighter one above and to the east of Castor. The remainder of the constellation Gemini is strung out above and to the west of Castor and Pollux for about 22 degrees.    

These two stars were venerated by the ancient sailors – mythology said they protected those who went to the sea in ships.  Shelley wrote: “When wintry tempests o’er the savage sea are raging, and the sailors trembling call on the Twins of Jove with prayer and vow…”   They even rate a mention in the Bible. In Acts Chapter 28, verse 11, Paul mentions that “... we departed in a ship... whose sign was Pollux and Castor.”     

Twins in mythology maybe, but the two stars couldn’t be more different. Pollux is closest at 36 light years and is a simple, unprepossessing giant star 35 times brighter than our Sun.  Castor, however, is a famous and fascinating multiple star, one of the most striking in the sky. While our naked eyes appear to see a single blue-white star 47 light years away, modest telescopes reveal it has two stars orbiting each other and a third orbiting the pair. Triplets! But there’s more… even more powerful instruments reveal that each of these three stars is in fact a binary – a very close pair of stars orbiting each other. Sextuplets!  

So nothing in space is ever at it seems, and there’s the fascination in astronomy.   

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