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Astronomy Picture of the Day


Photo of the Week.. The setting Sun hides in springtime clouds.

Astronomy news for the week starting Friday, June 21, 2002.

Phone: (217) 333-8789
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.

The Moon begins the week in its waxing gibbous phase, and passes through full on Monday, June 24th. At this full- moon passage, the Moon will experience another penumbral eclipse, during which the Moon will pass through the partial shadow of the Earth. In a penumbral eclipse, no part of the Moon ever falls into total shadow, so the Moon remains illuminated, and is just slightly dimmed. Such eclipses are of little interest, and at best are only barely visible. The only curious feature of this one is that it is one of two in a row. The Moon went through a penumbral eclipse the last full Moon on May 26th, and then we had a solar eclipse right in the middle, the two penumbral ones acting like bookends. This one is "visible" (if that is the right word) mostly in the eastern hemisphere, though eastern North America will witness a bit of it as well. A third penumbral eclipse takes place the night of November 19, leaving us with an unusual three lunar "eclipses" this year with none in total or even partial shadow (in which part of the Moon passes through the Earth's dark shadow).

Toward the end of the week, the Moon passes south of Neptune. Though the evening sky is dominated by Venus, you can still find Jupiter far down and to the right of it. The morning sky on the other hand has Mercury, which reaches its western greatest elongation on Friday the 21st. Though well separated from the Sun, the little planet will be hard to see low in the sky in bright eastern twilight.

It is the Earth that really takes the stage this week. Two hours before Mercury passes its elongation, at 8:24 AM Central Daylight Time (9:24 EST, 6:24 PDT), the Sun passes the summer solstice in Gemini, where it will be as far north as possible, 23.4 degrees north of the celestial equator. At that time, summer begins in the northern hemisphere, winter in the southern. The Sun will appear directly overhead at the Tropic of Cancer, and will (technically anyway) graze the horizon at midnight at the Arctic Circle. The north pole will receive maximum sunlight, while the south pole is in the grip of midwinter.

As the handle of the Big Dipper goes over the north pole in early northern evening, look in the space between the Big and Little Dippers (the latter contained by Ursa Minor) to find the tail of Draco, the Dragon. Between the Big Dipper's handle and the Little Dipper's bowl, you can admire Thuban, the star that lay at the pole in ancient Egyptian times nearly 5000 years ago, its current separation from the pole the result of the 26,000 year wobble of the Earth's axis.

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