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Astronomy Picture of the Day


Photo of the Week.. Bare trees lost themselves against a lacy sky (the fifth in a set of five panoramic cloudscapes).

Astronomy news for the week starting Friday, June 19, 2002.

Phone: (217) 333-8789
Prepared by Jim Kaler.

The Moon grows through its waxing gibbous phase the early part of the week, reaching full the night of Tuesday the 23rd after midnight in the Americas. The full Moon will therefore rise shortly before sunset that night and set just after sunrise. On Wednesday, the 24th, it passes south of Neptune in Capricornus. Last month's full Moon was the lowest of the year for those in northern latitudes, and this one will be almost as low, especially since the tilt of the lunar orbit brings it rather well below the ecliptic plane.

Summer full moons -- this one the Thunder Moon or Hay Moon -- often take on a beautiful coppery color. When the Sun or Moon are low above the horizon, you look through vastly more air then when these bodies are high in the sky. The air absorbs the blue component of sunlight and turns the Sun or Moon reddish, the effect greatly enhanced by high summer humidity.

The Sun "captures" a trio of planetary bodies this week. Jupiter, completely out of sight, passes conjunction with the Sun on Friday the 19th, of course far to the other side, about as far from us as it can get, some 6 1/4 Astronomical Units (the AU the distance between the Earth and the Sun). Almost exactly a day later, Mercury passes superior conjunction with the Sun. Mercury and Venus both go through two conjunctions, one when they are between us and the Sun ("inferior"), and again when they are on the other side ("superior"). Two days after Mercury's passage, Vesta, the brightest of asteroids, passes its solar conjunction as well. With all these disappearances, about all you can watch for is magnificent Venus, which rides high in the twilight evening western sky and is quite impossible to miss. About a month from now, the planet will pass its greatest angle from the Sun, when (because we then look at half the daylight and half the nighttime side) it will appear to us like a half moon. It is very close to that now.

Though the heat of summer is upon us, the late springtime stars still dominate the very early evening. Look for bright orange Arcturus, the luminary of Bootes, the Herdsman, now falling into the evening western sky. Most of the constellation appears as a large "kite" to the north of Arcturus, only two stars of the classic figure, Eta (Muphrid) and Zeta Bootis, splayed out to the south. As Arcturus sinks, white Vega and Deneb rise in the northeast, making the color contrast between them and Arcturus rather obvious, the "redder" color of Arcturus coming from a cooler gaseous surface.
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