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The Sky This Week, 2011 March 22 - 29

A change in the air


 Perigee Moon, 2011 March 19
Imaged with an Antares Sentinel 80-mm f/6
refractor telescope and a Canon PowerShot A95
digital camera from Alexandria, VA

The Moon moves into the morning sky this week, waning from her recent perigee performance. Last Quarter occurs on the 26th at 8:07 am Eastern Daylight Time. Luna spends the week skulking around the southerly reaches of the Ecliptic as she drifts among the constellations of the summer sky which are now becoming prominent before the start of morning twilight. She can be found just three degrees northwest of the ruddy star Antares over the south horizon at around 5:00 am EDT on the 24th. Two mornings later the Moon may be found just above the "Teapot" asterism of Sagittarius. By the end of the week look for the Moon low in the southeastern sky, rising about an hour before bright Venus as twilight begins to brighten the east.

As we work our way into the first full week of spring it’s hard not to notice how rapidly the dull shades of winter ate being replaced by sprouting bulbs and greening lawns. This is the time of year when many things undergo rapid changes, and among those are the constellations. The Sun is moving northward along the Ecliptic at its fastest rate for the year, adding an average of three minutes to the length of the day here in temperate northern latitudes. This has a noticeable effect on the winter constellations, which seem to tire of their watch over the long winter nights and yearn for a well-deserved rest. Orion and his bright cohorts are now confined to the western half of the sky, and by midnight the first stars of The Hunter begin to set. The eastern sky is much more sparsely populated with bright stars, with only three first-magnitude luminaries as opposed to the dozen that inhabit the sky around Orion. Regulus, Arcturus, and Spica will soon be the dominant stars of the night as the evenings become warmer and shorter.

You still have time to track down the elusive planet Mercury in the western evening twilight sky. The fleet planet reaches his greatest elongation east of the Sun on the 22nd, when he is about 18 degrees from our day-star. He now sets just at the end of evening twilight, so the best time to look for his is about half an hour after sunset, when he will be about ten degrees above the west horizon. You may need binoculars to pick him out, especially toward the end of the week, when he will have faded by over a full magnitude in brightness. Last week the MESSENGER space probe successfully entered orbit around Mercury, so keep an eye on the news to see what new wonders we’ll find on the solar system’s inner frontier.

By the end of the week Saturn rises just before 8:00 pm EDT, and by late evening he forms a colorful triangle with the bright, rose-tinted star Arcturus and blue-hued Spica, which lies about 10 degrees east of the ringed planet’s golden glow. Saturn will reach opposition on April 3rd, so each passing night brings him a little higher in the evening sky and closer to convenient observing hours. Saturn is a treat for any telescope, and this year his rings are opening up to present a good view of their structure for instruments of 3-inches or greater aperture. As you increase aperture you’ll see more detail, and you’ll also see more of the distant world’s small icy moons.

Venus still shines brightly before sunrise, but only in the gathering of morning twilight. She seems to be chasing the Sun and will continue to shine just before dawn for several more weeks to come.

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