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Third quarter

Photo of the Week. Third quarter Moon.

Astronomy news for the week starting Friday, March 1, 2013.

Sometimes the nightly sky excites, sometimes its quietness soothes; this week it is perhaps more of the latter. We do have a Moon that begins the week in the later stages of the waning gibbous phase, which ends at third quarter on Monday, March 4, with the Moon out of sight. Look for the near quarter that morning. It then spends the rest of the week as a waning crescent whose rising approaches ever closer to the start of dawn's light. The night of Friday the 1st, (and the morning of Saturday the 2nd) look for Saturn just to the east of the Moon. With the Moon passing south of the planet during the day of Saturday the 2nd in North America, the two will have changed places by the time they rise that evening. On Tuesday the 5th, the Moon will pass perigee, where it will be closest to Earth on its modestly elliptical orbit.

Jupiter and Saturn are still "it" for the naked-eye planetary sky. In the early evening, until it sets an hour after midnight, Jupiter dominates the heavens. Remaining north of Aldebaran and the Hyades, the Solar System's giant (carrying more than 300 times the mass of Earth) will gradually pick up speed to the east against the starry background. Then, around 10:30 PM, Saturn rises in the southeast, first to share the sky with Jupiter and then after Jupiter sets to glide alone toward its meridian passage (well to the east of Virgo's Spica) shortly before 4 AM. None of the other ancient planets (those known since ancient times) is visible, though Mercury at least makes a bit of a splash by passing inferior conjunction with the Sun (on the near side of the Sun) just a few hours before formal third quarter Moon on Monday the 4th.

Sure, March is here and the passage of the Sun across the Vernal Equinox in Pisces to mark the first day of spring is imminent. But in the early evening the Winter Triangle still glows in the southwest. Start with the brightest star of the sky, obvious Sirius (in Canis Major). Then look to the northwest to find bright reddish Betelgeuse (in Orion) and to the northeast for Procyon (Canis Minor). Farther up lies Gemini, whose classical figure traditionally holds the Summer Solstice (even though precession has technically carried it across the boundary with Taurus), allowing us to think of the much warmer days to come.
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