For the week including October 1, 2010

THe 10 The Loop 10 Location Larger Illustration

CETUS, THE SEA MONSTER

This time of year, around 10pm, the constellation of Cetus, the Sea Monster, is just above the eastern horizon. According to Greek myth, the sea monster was about to devour the beautiful princess Andromeda when it was slain by the hero Perseus. The legend of Perseus and Andromeda is one of the most enduring. There are half a dozen constellations visible in the north and east that commemorate it in one way or another.

Although the stars of Cetus don’t stand out in the sky, a careful hunt will allow you to pick out the faint loop of stars at the left side of the constellation that marks the head of the Monster. These stars are highlighted in red in our illustration. The rest of Cetus spreads across the horizon to the southeast. If you have a telescope, turn it on the orange giant star, Menkar, the brightest star in the loop. Very close by is a blue-white star that provides a striking color contrast.

Cetus is also home to Mira, the Wonderful. Hundreds of years ago, the star Mira (Latin for wonderful) was the cause of amazed confusion among astronomers. In 1603, it was included as a fairly bright member of Johann Bayer’s star atlas, the best sky map that had yet been produced. But by the time that the atlas was distributed, Mira had vanished! When astronomers had begun to think that Bayer had made a mistake, Mira reappeared in its designated position, but it was much dimmer than the star Bayer had described. To everyone’s astonishment, Mira grew in brightness over weeks and months until it exceeded his original description. Astonishment doubled when, before a year had passed, Mira performed a slow fade and passed from sight again. At the time, no other star was known to vary in brightness like Mira and it became a hot topic. When Galileo popularized the use of a new Dutch invention called the telescope in 1610, astronomers began to plot the star’s comings and goings. Every reappearance of Mira has been recorded since 1638 and it became the prototype of a class of stars called “Variables”. We know now that Mira is a huge star, the tenth largest known and 400 times larger than our Sun. This great size allowed the Hubble Space Telescope to give us a close up view. The image at lower left shows a hook of material extending from Mira toward a hidden, dimmer companion star. Mira’s brightness varies on a 330-day cycle and at times there is a considerable difference in its peak luminosity. In 1779, Mira’s peak almost succeeded in placing it among the ten brightest stars in the sky.

For the backyard astronomer, there is also a beautiful galaxy pair to see in this constellation:

The “10”: The Hubble Space Telescope photograph at upper right shows one of the strange sights to be seen in among the stars. Also known as Index Catalog object 298 and Arp 147, this pair of interacting galaxies is best known to astronomers as the “10.” According to computer simulations, several million years ago, the “1” galaxy crashed through the center of the “0” galaxy. It was left with a distorted core region and ring of stars encircling it. The “zero” galaxy was left with no discernible center and has spun itself into a circle of very hot, very young, blue-white stars.

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