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Photo of the Week. Summer thundercloud.

Astronomy news for the week starting Friday, July 25, 2008.

Passing last quarter during daylight (in North America) on Friday, July 25, the Moon begins to fade away as it enters its waning crescent phase and heads towards new on Friday, August 1, at which time it will totally eclipse the Sun and present a fine sight for people in Europe (Russia) and Asia (China), but not in North America. A partial solar eclipse will be visible in extreme northern North America, and will cover nearly all of Europe and Asia except for Spain, Portugal, and Japan. (Paired with this eclipse will be a partial lunar eclipse on August 16, which will be invisible in North America as well.) Back to home, the last glimpse of the thin crescent will be the morning of Thursday, July 31, in eastern twilight. Look next week for the waxing crescent in western evening twilight. On Tuesday the 29th, the waning crescent goes through perigee, bringing higher-than-usual tides to the coasts.

Of the ancient planets, the only one now readily visible is Jupiter, which is seen rising gloriously in the southeast in early evening. Bright and beautiful, hard to miss, Jupiter crosses the meridian to the south around 11:30 PM Daylight. Its retrograde, westerly, motion against the background stars has returned it to a lovely position just to the northeast of the Little Milk Dipper in Sagittarius, the locally bright stars making the planet's motion from week-to-week quite obvious. Of the "missing" bright planets, only Mercury makes some sort of news, as it passes superior conjunction with the Sun (on the other side of the Sun) on Tuesday, the 29th. Saturn and Mars are quite lost in evening twilight.

With the Moon nicely out of the way, we have a good chance to witness one of the better meteor showers of the year, the Southern Delta Aquarids, named after a southern star in Aquarius that marks the region of the sky from which the meteors seem to come (which involves the direction of the meteoroid stream about the Sun combined with the orbital motion of the Earth). The shower is visible from late July into early August with a broad peak around Monday, July 28, when under a dark sky it will produce perhaps 20 meteors a minute. The best time to look will be around 3 or 4 AM, to the south. The parent comet, from which meteor showers derive (as the comets slough off dust and rock), is unknown.

Summer is a fine time to catch the two celestial crowns. Look for a semi- circle of stars, Corona Borealis, the Northern Crown, to the northeast of bright Arcturus. Then if you have a good southern horizon and don't live too far north, look directly beneath the Little Milk Dipper of Sagittarius (now well-marked by Jupiter) to find the more ragged semi-circle of Corona Australis, the Southern Crown.
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