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Astronomy Picture of the Day

Earth Shadow

Photo of the Week.. The Earth's shadow, the gray band near the horizon, sets over the Pacific Ocean just before sunrise.

Astronomy news for the week starting Friday, May 3, 2002.

Prepared by Jim Kaler.

If you like stars, go to STARS: Portraits of Stars and their Constellations, compiled from previous stars of the week. Enjoy photographs of the January 20, 2000 total eclipse of the Moon. Watch planets move against the background stars. See sunsets, rainbows, the Moon and planets, and other sky phenomena in Sunlight.

We begin the week with the Moon in its last quarter, the phase reached about the time of Moonrise in North America the night of Friday, May 3. The rest of the week sees the lunar disk waning as a crescent toward its new phase, the Moon dropping ever lower in the eastern sky near dawn.

The Moon, however, takes a distinct second place to what is happening in the evening western sky. The night of Sunday, May 5, in mid- twilight, find reddish Mars, Saturn, and brilliant Venus all tucked together into a tight triangle, Mars on top, Venus the brightest. The bright star Aldebaran will be almost directly below Saturn, while down and to the right, on a line from Mars through Venus, is Mercury, which achieves its best visibility and greatest elongation to the east of the Sun that same night. During the week, it will be easy to see all these planets shift in relative position, Venus and Mercury orbiting this side of the Sun, Mars far to the other side. Then watch the conjunctions. Venus passes 6 degrees north of Aldebaran and Mars passes 2 degrees north of Saturn during the day of Saturday, May 4th, making them the closest for us that evening and on the previous night as well. Then the night of Tuesday, the 7th, we see the closest approach between Venus and Saturn, when the ringed planet will be 2 degrees to the south of its temporary neighbor. Looking ahead a bit, then find Venus passing only three-tenths of a degree to the north of Mars the night of Friday, May 10. While all this action is taking place, Jupiter rides high above, still placed against the bright stars of Gemini. We will not get as good a look at all the traditional naked-eye planets for a long time. None of these close passages has any real physical meaning, but the aesthetic meaning is undeniable.

With the morning sky becoming more accessible with the dimming of the Moon, you might get a binocular glance at Comet Ikeya- Zhang, which is coursing in the northeast toward and through Draco. And with luck you might see a few meteors of the Eta Aquarid shower, which peaks early in the week (the mornings of May 3 to 6) with a maximum of perhaps 10 per hour visible.

As the evening planets gather, you can also admire that icon of the Northern Hemisphere, the Big Dipper. The grand figure, known in Britain as the Plough (which it resembles as much as it does a Dipper), is an asterism -- an informal constellation -- of Ursa Major, the Great Bear. Unlike most constellations, many of the stars of the Bear are physically related, and are part of the Ursa Major cluster, the chief members being the five inner stars of the Dipper. Other examples of constellations with related stars are Orion of northern winter, his mythical nemesis Scorpius of northern Summer (the two made in part of loose "associations" of hot stars), Perseus of autumn, and Coma Berenices of spring, both of which are made in part of real star clusters.

Do you have a favorite star or one you would like to see highlighted on the Star of the Week? Send a suggestion to Jim Kaler.
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