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Astronomy Picture of the Day

Solar Eclipse

Photo of the Week.. The "sunset eclipse" of June 10, 2002, as seen from Urbana, Illinois. Courtesty of P. Larry Nelson.

Astronomy news for the short week starting Sunday, August 18, 2002.

Skylights will resume its normal schedule on Friday, August 23. Thank you for your patience.

The sky is rather busy in spite of a shortened week. The Moon waxes through its gibbous phase during most of it, reaching full on Thursday August 22 shortly before moonrise in the Americas, causing the Moon to rise shortly after sunset. Eight hours before full phase is achieved, the Moon passes four degrees to the south of Uranus, which now lies close to the Capricornus-Aquarius border. The bright Moon will, however, make the distant planet quite impossible to see. About a day and a half before that, the night of Tuesday the 20th, the Moon will do the same to Neptune, which is firmly ensconced in Capricornus.

That the near full Moon passes Uranus obviously means Uranus too is opposite the Sun. On Monday the 19th, the planet, now in full retrograde motion, will pass its formal solar opposition. Not to be outdone by such a dim planet, Venus reaches its greatest elongation east, when it is 46 degrees to the east of the Sun, the same day as the full Moon, on Thursday the 22nd, allowing a grand view of the evening sky both to the east (for the Moon) and to the west (for Venus). This time of year, however, the ecliptic, near which the planets move, lies rather flat against the northern hemisphere western evening horizon. As a result, Venus will not be all that high in the sky even though it is at its greatest angular separation from the Sun. At that time, the telescope will show Venus in a "half phase," that is, we see half the daylight side, half the night. Though the Sun will now begin to catch up with Venus, the planet will continue to brighten for another month as it gets closer to the Earth, reaching greatest brilliancy on September 26. During this time the planet is seen telescopically as a continuously slimming crescent.

Venus and the Moon provide us with subtle and little-known lighting effects. The blue sky is caused by the blue component of sunlight scattering off the Earth's atmosphere. The Moon is illuminated by reflected sunlight, and in very clear sky away from artificial lighting, you can see the sky take on a bluish cast. Once the Moon is out of sight, Venus is so bright that in a fully darkened sky, trees and other objects will cast Venusian shadows on the ground.

Look to the south in early evening to see Scorpius dominating the landscape, Antares at its heart, the great hook of its tail nearly grazing the southern horizon for those in middle northern latitudes.

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