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The Sky This Week, 2010 April 13 - 20

Global Astronomy Month continues, the Moon returns to the evening sky.
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"Evening Colors" at the USNO
Every evening, at local sunset as determined by the Nautical Almanac Office and timed by the USNO's Master Clock, the U.S. flag is lowered accompanied by the sound of a lone bugle sounding "Retreat".

The Moon waxes in the evening sky this week, leaping quickly up into the evening twilight among winter’s departing stars. First Quarter occurs on the 21st at 2:20 pm Eastern Daylight Time. See if you can spot Luna’s 36-hour old crescent within a degree of fading Mercury in the deepening twilight of the evening of the 15th. Mercury will have faded to about magnitude 1.5 by this time, so you’ll probably need binoculars to glimpse him just below and to the left of the Moon’s slender arc. On this evening Luna will be some seven degrees below and to the right of dazzling Venus; on the following night you should have no trouble spotting a slightly fatter crescent Moon at a similar distance almost directly above the brilliant planet. By the week’s end the Moon is drawing a bead on ruddy Mars, who is once again gaining speed in his eastward dash against the background stars.

April is Global Astronomy Month, a program that evolved from last year’s extraordinarily successful "100 Hours of Astronomy", one of the cornerstone projects of the International Year of Astronomy. Sponsored by Astronomers Without Borders, GAM continues in the spirit of last year’s worldwide event where over one million people looked through telescopes, most for the first time. Here at the USNO some 9000 people turned out for our Open House, far outstripping our wildest expectations. We won’t be hosting such an event this year, but there are many opportunities to see the night sky over the next few weeks through the telescopes of local amateur astronomers. Every Friday, weather permitting, the Analemma Society in Great Falls, VA hosts public viewing from their site Observatory Park at Turner Farm, close to the intersection of Georgetown Pike and Springvale Road. On Saturday night the National Capital Astronomers will host "Exploring the Sky" at the Rock Creek Nature Center, just off Military Road in Northwest DC, and on April 24th the Northern Virginia Astronomy Club will sponsor their Astronomy Day observance at Sky Meadows State Park. Take advantage of the Moon’s crescent phases to enjoy the changing constellation scene as winter’s brighter stars give way to the more subtle patterns of spring. This past weekend I had a chance to take my 14.5-inch telescope out to the country to explore the distant galaxies that lie far beyond the patterns of Leo and the Big Dipper; next weekend I’ll be poking around lunar craters and exploring the rings of Saturn.

Mercury rapidly fades in the evening twilight this week. You’ll probably be hard-pressed to find him once the Moon deserts him after their close encounter on the 15th. The fleet planet will return to the evening sky twice more this year, but it won’t be until December that he will be as prominent as he has been the last few weeks.

Fortunately, brilliant Venus is easily seen in the evening sky. She is gradually climbing away from the Sun and sets a few minutes later each night. She will be a fixture in the west and southwest sky until the fall. In late summer she’ll overtake mars and Saturn for a spectacular twilight planetary grouping.

Mars continues to shine high in the south as twilight fades. He’s now trekking eastward away from the Gemini Twins of Castor and Pollux. He’s still much brighter than either star, and his distinct color sets him apart from any other bright object in this part of the sky. This week he passes to the north of the well-known "Beehive" star cluster, which should provide a very nice view through a pair of binoculars.

Saturn occupies a large, relatively empty section of the sky southeast of the tail of Leo, the star Denebola. The ringed planet forms a triangle with the bright stars Arcturus and Spica in the later hours of the evening and crosses the meridian at around 11:30. He’s very well placed for telescopic viewing and will be one of the highlights for Global Astronomy Month activities.

Finally, giant Jupiter greets very early risers out for a pre-dawn stroll. He’s low in the east as first light begins to envelope the land. Save him for summer, though. That’s when he’ll be at his best!

USNO Master Clock Time
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