Skylights featured on Astronomy Picture of the Day

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Winter Triangle

Photo of the Week. The Winter Triangle disappears as we leave the cold behind.

Astronomy news for the week starting Friday, April 8, 2011.

The Moon grows as a fat waxing crescent through first quarter the morning of Monday, April 11th, well after moonset in North America. The evening of Sunday the 10th it will therefore appear a bit short of first quarter, while the following night it will be seen a bit after the perfect phase. It thence waxes in the gibbous phase, full Moon not reached until Sunday the 17th. The night of the 10th, look for the near-quarter to the south of Gemini's Castor and Pollux as it prepares to pass between the mythical warrior twins and Procyon in Canis Minor farther to the south.

The extreme ends of the planetary system come into play this week as the innermost, Mercury, goes through inferior conjunction with the Sun (more or less between us and the Sun) on Saturday the 9th, while half a day earlier, dim Pluto (dare we call it a "planet"?) starts its tiny retrograde motion (to the west against the stellar background). Slowly working its way through northern Sagittarius to the north-northwest of the Little Milk Dipper, Pluto, at dead-on 14th magnitude, is some 1500 times fainter than the human eye can see without optical aid. Now called a "dwarf planet," Pluto really belongs more to the extended Kuiper Belt of debris that orbits beyond Neptune.

Having gone through opposition with the Sun last week, Saturn now rises a bit before sunset, so is nicely up in the east as the sky darkens. Look for it crossing the meridian to the south around 12:30 AM Daylight Time followed to the southeast by Spica, the two making a fine sight, the planet almost twice as bright as the star. With Jupiter, Mercury, and Mars too close to the Sun to be seen, that leaves us with Venus. Now not rising until half an hour after twilight begins to brighten the sky, the planet is getting difficult to see without good timing and a good horizon.

Procyon, which will be visited by the near-quarter Moon, is the northeastern anchor of the famed Winter Triangle, which consists of it, Betelgeuse in Orion, and Sirius in Canis Major. The Triangle encloses a good part of the dim, modern constellation of Monoceros, the Unicorn that, while relatively obscure, hosts a variety of fine stellar and interstellar sights that include associations of newly-born stars.
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