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Jimmy Westlake: Sea monster fills eastern sky

The sea monster Cetus fills up our eastern and southeastern sky during the early evenings this month. Look for the star Tau Ceti — a near twin of our sun — and the variable star Mira

The sea monster Cetus fills up our eastern and southeastern sky during the early evenings this month. Look for the star Tau Ceti — a near twin of our sun — and the variable star Mira, near the limit of naked-eye visibility.

Wedged in between the bright star Fomalhaut to the south and the glittering Pleiades star cluster to the east is the huge, lumbering constellation of Cetus the Whale. It ranks fourth in overall size among the 88 official constellations; only Hydra, Ursa Major and Virgo cover more area of the sky. But despite its large size, Cetus claims no star brighter than second magnitude, and it has only one of those.

Since the earliest times, Cetus has been identified with the mythological beast created by Poseidon because of Queen Cassiopeia's boasting that her daughter Andromeda was more beautiful than Poseidon's daughters. The only way to stop the monster's killing spree was to sacrifice the lovely Andromeda to him. While Andromeda was chained to the rocks at the seashore and awaiting her fate, the hero Perseus suddenly swooped in on Pegasus the Flying Horse and dangled the severed head of Medusa before Cetus. The monster was transformed instantly into a mountain of stone.

The original mythological Cetus was a sea monster and bore little resemblance to a whale. But 17th century astronomers chose to portray the image of a whale among these stars, and the image stuck. There are some ancient references that identify our Cetus the Whale as the giant cetacean that swallowed Jonah in the well-known Old Testament story.

During late October, Cetus has risen completely above our southeastern mountains by 9 p.m. Its brightest star is Deneb Kaitos, the whale's tail, visible just east of the brighter star Fomalhaut. From there, the whale extends some 40 degrees to the north and east to the star Menkar, the whale's nose. Menkar and four other stars form a distinctive pentagon shape that represents the head of the sea monster.

There are two particularly interesting stars within the constellation of Cetus. First is the star Tau Ceti, a near twin of our own sun and easily visible to the unaided eye. Because it is nearly the same size and temperature as our yellow sun and only 12 light years away, Tau Ceti makes an intriguing target for astronomers searching for Earth-like planets. One day, Tau Ceti might become home to a space colony when we leave our cradle behind. So far, no planets have been identified orbiting Tau Ceti, but a large ring of rocky debris, not unlike our own asteroid belt, has been detected. Tau Ceti has figured heavily in many science fiction stories in the past and no doubt will continue to capture the imagination of stargazers and dreamers everywhere.

The second star of note within the borders of Cetus isn't even visible to the naked eye except for a few weeks each year. It is Omicron Ceti, also known as Mira the Wonderful Star. Mira is a long-period variable star that first caught the attention of astronomers many centuries ago. When near maximum light, Mira sometimes can rival Cetus' brightest star, Deneb Kaitos, though it typically maxes out slightly fainter. When near minimum light, a telescope is needed to spot Mira at all. This remarkable star oscillates between these two extremes in a period of about 11 months. Mira was near its peak brightness back in August and now is fading. A sharp eye still can pick it out near the limit of naked-eye visibility.

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. Check out Westlake's astrophotography website at http://www.jwestlake.com.