Cetus and Tau Ceti

Ris­ing low in the south­ern sky this month is one of the most unusual of the old con­stel­la­tions. The oceans rep­re­sented vast­ness and dan­ger to the ancient Greek peo­ple. As they looked south into the great waters of the Mediter­ranean, they invented a pat­tern of stars that rep­re­sented the awe and fear that they felt.

It is the mighty Cetus, the whale, ris­ing out of the great deep. Before mid­night you can find him spread out over a large expanse of the south­east­ern sky. A cir­clet of five stars forms his large head. He has a long, skinny body formed by a line of stars stretch­ing to the west and end­ing in a rather fat tail.

Our mod­ern iden­ti­fi­ca­tion of him as a whale is, well, kind of fishy. The Greeks couldn’t have had much expe­ri­ence with whales.

More likely, they saw him as a sea mon­ster that rose majes­ti­cally from the waters in the autumn and dove back in the late winter.

He is pic­tured in an 18th cen­tury star map as a weird com­bi­na­tion of dif­fer­ent ani­mals. He has an enor­mous head, with a large open mouth and rather formidable-looking teeth. He has claw-like front feet and a scaly body like a lizard, end­ing with a long, curved tale like a sea serpent.

He acted as a grotesque and scaly hit­man for Posei­don, the god of the sea.

His great­est bat­tle is a whale of a good story, a tail, er, tale, of brav­ery and self sac­ri­fice. Cas­siopeia was the Queen of Ethiopia. She is vis­i­ble as a “W” of stars high in the north­ern sky. She spouted off that she was more beau­ti­ful than the Nereids, hand­maid­ens to Poseidon.

He didn’t have much of a sense of humor about such things, so he sent Cetus to rav­age the coast­line of Cassiopeia’s domain. Androm­eda, Cassiopeia’s daugh­ter and a con­stel­la­tion vis­i­ble in the east­ern sky, was chained to a rock near modern-day Tel Aviv to act as a mid-afternoon snack for the mon­ster. In this way, it was hoped that Neptune’s anger would be assuaged.

Androm­eda faced her fate with­out blub­ber­ing. (Will these bad whale puns never end?) Luck­ily for her, the great hero Perseus (just to the east of Cas­siopeia in the sky) came fly­ing down on the winged horse Pega­sus (just to the south of Androm­eda). He dis­patched Cetus, saved the inno­cent Androm­eda, and mar­ried her.

The Ethiopi­ans no doubt had the world’s largest fish din­ner at the wed­ding. One can imag­ine the solic­i­tous Cas­siopeia ask­ing Perseus, “And how do you like your sea mon­ster, del­i­cately poached in but­ter or deep fried with a side of tar­tar sauce?”

Cetus pos­sesses an inter­est­ing vari­ety of astro­nom­i­cal objects to observe, but none is more famous than Tau Ceti, espe­cially to science-fiction buffs.

Many sto­ries have been writ­ten about it because the star is the clos­est likely can­di­date to have plan­ets like our sun does. Eas­ily vis­i­ble to the naked eye, it is the bot­tom left star in the tail of Cetus.

Tau is one of the clos­est stars to our sun at about 12 light years away, or a mere 70 tril­lion miles. Like our sun, it has reached a nice, respectable mid­dle age. At about about 90 per­cent of the sun’s size but only about 45 per­cent of its bright­ness, Tau has strik­ing sim­i­lar­i­ties to our daystar.

In 1959 the astronomers of Project Ozma lis­tened with their radio tele­scopes for sig­nals from intel­li­gent crea­tures like us. Sci­en­tists and explor­ers may look there some day for Earth-like plan­ets if we ever send mis­sions beyond the reaches of our solar sys­tem. If one exists, it is about .75 the dis­tance from Tau as Earth is from our sun.

Two recent dis­cov­er­ies make a twin of Earth a bit less likely. Var­i­ous attempts, includ­ing those of the Kepler Space Tele­scope, have dis­cov­ered hun­dreds of plan­ets orbit­ing other stars. How­ever, small stars like Tau turn out to be dif­fi­cult tar­gets for such examinations.

Instead, Kepler has dis­cov­ered many gas-giant plan­ets inex­plic­a­bly close to their par­ent stars. Such Jupiter-like plan­ets would sim­ply absorb Earth-like plan­ets or cast them out of the hab­it­able zone.

Also, in 2004 British astronomers dis­cov­ered a disk of cold dust and debris around Tau. Such a disk might have formed plan­ets like Earth in the first place. How­ever, its pres­ence now would make for an extra­or­di­nary num­ber of meteor falls on any extant planet. The planet may be there, but life would find it dif­fi­cult to form.

To the ancients, Cetus rep­re­sented the fear of the great waters, a vast expanse of ocean filled with unknown dan­gers. The same turns out to be true of the vast­ness of space. The orig­i­nal dis­cov­ery of plan­ets orbit­ing other stars cre­ated great hope that other life might be out there. So many things can go wrong that get­ting a foothold might be life’s great­est challenge.

Tom Burns is the direc­tor of Perkins Obser­va­tory. He can be reached at tlburns@owu.edu.

Posted by Tom Burns on Oct 7 2012. You can follow any responses to this entry through the RSS Feed. Comments can be made below.