Adrian Berry  
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The Green Star

ONLY one star visible to the naked eye is indisputably green. This is Zuben el Chamali (or Zubenelg), otherwise known as beta Librae, 160 light years away in the southern skies. I got this arcane piece of information from Michael E. Bakich's Cambridge Guide to the Constellations, one of the most fascinating astronomy reference books I have ever seen.

It contains everything - and much more - that one could possibly want to know about the constellations, and the stars and other objects that they contain. Here, for example, is a list of the 200 nearest stars (most reference books list only 50), the 200 brightest stars, an alphabetical list of hundreds of star names with their designations, and the three specific references to the constellations that appear in the Bible. (Two are in Job and the third is in Amos.)

I had forgotten, until reading this book, that the present 88 constellations the International Astronomical Union decided upon in 1928 were preceded by 50 other constellations; some that are now extinct, and others that were merged or divided to form the present ones. Some of these had extraordinary origins. 


The Roman emperor Hadrian

Antinous (now part of Aquila) was named after a homosexual slave and lover of the Roman emperor, Hadrian, who drowned himself in the Nile in the hope that the gods might prolong his master's life. Cur Caroli (now Canes Venatici) commemorated the martyrdom of Charles I. The brightest star in Canes Venatici still bears the name ``the crowned heart of Charles.'' Another English royal constellation was Robur Carolinum (now in Carina) representing the Royal Oak of Charles II who supposedly hid a day and a night in this tree after his defeat by Cromwell at the Battle of Worcester. One possible reason for abolishing this constellation is that barely an oak tree in England was not claimed as the king's hiding place after the battle!

And I was surprised to learn also that, including the 12 zodiacal constellations, the Moon passes through a total of 18, the visible planets through 24, and Pluto through no less than 41. (I'm sure that astrologers could make something of this if only they knew it.)

It is well known that some constellations are much richer in interesting objects than others, but Mr Bakich gives the exact figures. The most interesting is Centaurus, with 101 stars visible to the naked eye; and the most boring is Caelum, with only four.

And for another way of looking at it, Hydra is the biggest constellation, comprising 3.2 percent of the sky or 1,303 square degrees; and Crux is the smallest, with only 0.2 percent or 68 square degrees. I don't know whether these facts are of any practical use, but reciting them might well create a noticeable effect at a cocktail party.

So why is the star Zuben el Chamali green, the only known star in the Universe to be so? Mr Bakich does not know. He has contented himself with observing it and questioning other observers of it, and they all agree about its unique colour.

But if anyone can tell me why, of 3,047 naked eye stars, one, and only one, is green, I should be very interested to hear.

 

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