D e s e r t E x p o s u r e 
March 2006
D e s e r t E x p o s u r e |
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 Constellation of the Month: Taurus, The Bull (Part II) This month we will take a second look at the constellation Taurus. Instead of looking at the whole constellation, we will look at its two major open clusters, the Pleiades and the Hyades.
Mythologically, the Pleiades were the daughters of the Titan Atlas and the sea-nymph Pleione. Atlas had led the Titans in a war against Zeus and the other Olympians. The Titans lost, and Zeus forced Atlas to hold up the sky forevermore. One day when Pleione and her daughters were playing in a field, the hunter Orion came upon them and was taken by their beauty. He began pursuing them endlessly. Zeus eventually noticed the Pleiades' plight and changed them (and their mother) into doves to escape Orion's advances. Zeus then turned them into a small group of stars near the horns of Taurus. Atlas was doubly punished, not only having to hold up the sky, but losing his wife and daughters to the sky as well. While there are seven Pleiades (Maia, Electra, Alcyone, Taygete, Asterope, Celaeno and Merope), there are only six stars readily visible to the naked eye. There are two stories about the missing Pleiad. One is that while the other Pleiades had taken lovers from among the gods, Merope had consorted with a mortal, Sisyphus, king of Cornith. To hide her shame, she fled from her sisters. A different story has Electra being an ancestress of the royal house of Troy. After the Greeks destroyed Troy, Electra was so saddened by the loss that she abandoned her sisters. She became a comet, and comets were thereafter known to portend doom whenever one became visible. The Hyades are another group of daughters of Atlas and Pleione. These daughters also had a brother, Hyas. When Hyas was killed by a wild boar he was hunting, the Hyades (Phaola, Ambrosia, Eudora, Coronis and Polyxo) were so grief-stricken they died of sadness. Zeus then put them up into the sky. There, they portend the rainy season, with their tears of sorrow falling softly on the Earth as rain. Later, Thione and Prodice were added to the Hyades. They are daughters of Hyas and Aethra (one of the Oceanides), who were also saddened by the loss of their father. Open clusters are the kindergartens of our galaxy. Giant clouds of dust and gas (mostly hydrogen) reside in the galaxy's spiral arms. When a nearby star goes supernova, the shock waves expand outward from it and can strike one these gas clouds, compressing the cloud and beginning the process of star formation. As the cloud collapses, individual areas of higher density randomly form and their gravity pulls in increasing amounts of dust and gas, forming huge gas balls. Eventually, the core of these gas balls gets so hot from the compression caused by the weight of the gas above it, that it starts to fuse, converting hydrogen into helium, and a cluster of stars is born. Since all these stars came from the same gas cloud, they all have the same motion as the original cloud, and move together through space. This grouping is called an "open cluster." Eventually the gravity of other stars in the galaxy causes them to spread out, and finally they lose their group identity to join the background of stars in the galaxy. The Pleiades consists of over 500 stars in an area two degrees across, but the brightest stars fit into the central one degree. The Pleiades cluster is about 2,200 trillion miles away, just down the block in astronomical terms. The cluster has a low density, and the gravity of the surrounding stars will tear it apart in the next 250 million years. Pictures of the Pleiades often show the remains of the dust cloud that formed them, still reflecting their light some 100 million years after they formed. Spread across five-and-a-half degrees in our sky, the Hyades are only
870 trillion miles away and some 790 million years old. The hallmark
star of Taurus, its red eye, Aldebaran, appears to be in the Hyades,
but it is actually two and a half times closer to us. The Hyades are
moving toward a point just east of Betelgeuse in Orion. The Planets for March 2006 The bright star in our morning sky is the planet Venus. After having been in the evening sky most of last year, Venus will grace the morning sky for most of this year. Venus has a thickening crescent shape, shrinking slowly as the days go by and it pulls away from the Earth. Starting the month in Sagittarius, Venus will move rapidly into Capricornus and then Aquarius. At midmonth, Venus will be magnitude -4.5 and 27.6 seconds-of-arc across, a full third smaller than it was last month at this time.
Mars is in Taurus this month, beginning almost between the Pleiades and Hyades. It passes the Hyades around March 7, some seven degrees from Aldebaran. Mars is high in the west, and sets around 12:30 a.m. as it slowly fades and gets smaller. Still obvious at magnitude 1.0, the Red Planet is now only 6.3 seconds-of-arc across. High in the east at sunset, Saturn is shining at magnitude -0.3 in the constellation Cancer. Telescopically, Saturn is a stunning sight, with the ball of the planet 19.6 seconds-of-arc across and the rings 44.4 seconds-of-arc across with the southern face showing. The rings are tilted up 20 degrees to our line-of-sight. Jupiter comes up around 11 p.m. and is visible the rest of the night. Still in Libra, Jupiter will be at magnitude -2.3 and 41.2 seconds-of-arc across. The Earth is slowly catching up with Jupiter, and so the King of the Planets is growing larger and brighter when viewed through a telescope. Now is the time to start observing the constantly varying cloud patterns on Jupiter's surface with your telescope. So put on your heavy jacket, enjoy the early-morning spectacle, and "keep watching the sky"!
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