Skylights featured on Astronomy Picture of the Day

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Skylights featured five times on Earth Science Picture of the Day:
1 , 2 , 3 , 4 , 5


Photo of the Week. Copernicus, who told the world of a heliocentric Solar System, watches the skies outside Adler Planetarium in Chicago.

Astronomy news for the week starting Friday, December 7, 2001.

We begin the week with the Moon passing its third quarter today, Friday, December 7. It will then wane through the crescent phase, daily becoming closer and closer to the eastern morning horizon. The Moon is heading toward a rendezvous with the Sun, as when it passes new next Friday the 14th, it will also pass across the Sun to produce an eclipse that will be seen as partial throughout nearly all of North America. Be sure to se aside a bit of time next Friday afternoon to watch, at sunset in eastern North America, late afternoon on the west coast -- providing of course that you have either a professionally made filter or you watch by projection. The amount of Sun covered varies from a few percent in Canada to 40 percent in the southern US, while Hawaii -- the place to be -- will see near full coverage.

It never ceases to amaze how long Mars hangs around after it passes its opposition with the Sun. Not all that much farther from the Sun than the Earth, our planet only slowly pulls ahead of it. As a result, and as a result of the planet moving northward, the setting time only slowly becomes ever-earlier. The red planet, which has just passed from Capricornus to Aquarius, is still nicely visible in the southwest, setting shortly after 10 PM. The early evening is therefore graced with all the outer planets except Pluto, as Saturn now rises before sunset, Jupiter, in Gemini, following just before 7 PM. Uranus and Neptune, both in Capricornus, both set shortly before Mars.

Saturn, in Taurus, moves within a rich field of stars. The constellation is host to the two top open clusters, the Pleiades, or Seven Sisters, a very obvious patch of modestly bright stars, and the Hyades, which lie just to the west of Saturn. Because the Hyades cluster is only a third the distance of the Pleiades, a mere 150 light years, its stars are more spread out. Older too (about half a billion years), it lacks the sparkle of the hot massive blue stars that the youthful Pleiades (closer to 100 million years) contain. (More massive stars die at younger ages.) The Hyades seem to be highlighted by the orange first magnitude giant star Aldebaran, but that is only a line-of-sight coincidence, as Aldebaran, fainter than Saturn in apparent brightness, is only 60 light years away, less than half the distance to the Hyades. The Hyades has a long and important history in astronomy, as the cluster provides an important stepping stone in the celestial distance scale. It is so close that we can see the paths of the stars slowly converging to a point in the distance -- a perspective effect -- from which a distance to the cluster can be derived. While admiring Taurus and its clusters, be sure also to watch out for Orion, the bright red supergiant Betelgeuse, at Orion's northeast corner, rising about the same time as Jupiter.
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