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Photo of the Week. Day's end.

Astronomy news for the week starting Friday, February 22, 2013.

This is the week of the full Moon, which takes place during the day on Monday, February 25, with the Moon out of sight. That evening, the Moon (the Sap Moon, Crow Moon) will rise slightly past full (but so close to it as to make an unnoticeable difference). Prior to that time, the Moon will wax in its gibbous phase, while afterward it will wane in the gibbous, rising ever later after sundown as it heads towards third quarter next week.

Though the bright Moon will wash out the stars, making the fainter ones invisible to the naked eye, note one beautiful encounter that will take place between the waning gibbous and the first magnitude star Spica (the luminary of Virgo) the evening of Thursday the 28th, when the star will appear to hang on the Moon's northern edge. They will be closest around midnight. Spica will actually be occulted as seen from Central America and points downward. If you can, use binoculars. The closeness of the two allows us to see lunar orbital motion in real time, as the Moon traverses to the east (against the stars) by its own angular diameter in an about an hour. By the time it sets, the Moon will have moved notably to the east of the star. As the Moon and Spica head across the celestial vault, look for Saturn (the brighter of the two) further to the east of them.

The two outer planets, Saturn and Jupiter, now rule the planetary sky, the three inner planets ( Mercury, Venus, and Mars) all too close in line to the Sun to be readily visible. But the big two make up for it. Dominating the western sky, luminous Jupiter (other than the Moon the brightest thing up there) does not set until about an hour after midnight. Look for orange Aldebaran and the Hyades cluster still to the south of it. With dimmer Saturn (but at magnitude zero, currently brighter than all but the eight brightest stars) rising about an hour BEFORE midnight, for about two hours the giants of the Solar System share the sky. In the morning, look about an hour before dawn for Saturn to cross the meridian to the south as it trails Spica across the sky.

With spring fast approaching, we begin to take leave of the winter stars and look to those of spring. Yet in early evening, Orion still looks down upon us. He is bordered to the east by one of the more obscure constellations, and certainly one of the dimmer, Monoceros, the Unicorn. Somewhat obscure it may be, but it hosts some of the hottest and most luminous stars of the sky, including S Monocertis and Plaskett's Star, in addition to the beautiful Rosette Nebula. You still of course have plenty of time to admire Sirius, the brightest star of the sky to the southeast of the Hunter.
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