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Astronomy Picture of the Day

Country sky

Photo of the Week.. Country summer sky (the second in a set of five panoramic cloudscapes).

Astronomy news for the week starting Friday, June 28, 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 wanes through its gibbous phase the early part of the week, passing its third quarter on Tuesday, July 2, shortly before moonset in the Americas, the Quarter visible in the daylight western sky. Since the Sun has just passed the summer solstice in Gemini, this third quarter will be seen just past the vernal equinox in Pisces. It thereafter begins to wane through its crescent phase as it descends the early morning sky. Just 9 hours before the quarter, the Moon passes apogee , where it is farthest from the Earth.

The configuration of the Sun and Moon conspire to produce some of the year's weakest ocean tides. Tides are produced by the gravitational stretching action of the Moon and Sun on the Earth's waters, making them flow more or less to points beneath the two bodies. Tidal amplitudes at the shore are always at their cyclical strongest when the Sun and Moon are aligned (full and new Moons) and weakest when the two work at cross-purposes, at the quarters, when the solar tide acts to fill in the more-powerful lunar tide. In addition, tides are very sensitive to the distances of the tide-producing bodies. With the Earth approaching aphelion on Friday, July 5, where it is farthest from the Sun, both bodies will also have their weakest tidal effects.

This week is full of invisible passages. On Friday, June 28, the gibbous Moon passes 4 degrees south of Uranus, all but washing out the faint planet. Then on Tuesday, July 2, in between lunar apogee passage and the time of the third quarter Moon, Mercury passes just 0.2 degrees south of Saturn, the event lost in morning twilight. The next day, on Wednesday, July 3, Mars passes less than a degree to the north of Jupiter, but that will be lost in western twilight. The following day, in celebration of the Fourth of July, Mars swings north of the star Pollux in Gemini. The only planet left standing is Venus, the brightest of them all. Impossible to miss in the west after sundown, this second planet from the Sun does not now set until nearly 11 PM Daylight time.

The bright orange-colored star that announces spring, Arcturus in Bootes (the Herdsman), the brightest star of the northern hemisphere, lies just past the meridian to the south at 9 PM. It is challenged by the luminary of summer, white Vega in Lyra (the Harp or Lyre), which is only marginally fainter than Arcturus and is now seen rising in the northeast in early evening. Between Lyra and kite-shaped Bootes is mighty Hercules, one of the oldest constellation figures known, and the semi-circular ring of stars that makes Corona Borealis, the Northern Crown, which represents the crown of Princess Ariadne.

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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