Skylights featured on Astronomy Picture of the Day

Scout Report Selection Webivore Selection SpaceCareers Selection

Skylights featured on Earth Science Picture of the Day: 1 , 2 , 3 , 4 , 5 , 6 , 7


Photo of the Week. Rainbows don't need rain; just Hawaii and enough moisture in the air.

Astronomy news for the week starting Friday, December 1, 2006.

Welcome to December and to what is sometimes called "meteorological winter," though astronomical winter, marked by when the Sun crosses the Winter Solstice in Sagittarius, does not begin until December 21.

We begin a week of the full Moon (the "long night Moon," the "cold Moon"), the phase passed the evening of Monday, December 4, right about the time of Moonrise in North America, the Moon therefore rising opposite the Sun almost exactly at sunset -- and setting the following morning just after sunrise. Early in the week the Moon waxes gibbously, and later in the week, after full, gibbously wanes. Before full phase, the eastern edge is the sunrise line, while after full the western edge is the sunset line. Almost exactly three days before full, on Friday the 1st, the Moon passes perigee, where it is closest to the Earth.

While until Solstice passage the days continue to shorten, the earliest sunset actually takes place around Thursday the 7th. The difference is caused by the eccentricity of the Earth's orbit combined with the tilt of its axis, resulting in the actual position of the Sun being to the west of its average position as projected on the celestial equator. We make up for it, in that the latest sunrise does not take place until a couple weeks after Solstice passage.

Following Mercury's brief appearance last week, it is now quickly disappearing into twilight to join Jupiter and Mars, which, rising in mid-dawn, are effectively invisible (as is Venus). That, once again, leaves us with Saturn. Now rising just after 10 PM, the ringed planet is making a nice return to the evening scene. Saturn is beautifully placed in western Leo just to the east (and a bit north) of somewhat dimmer Regulus. Look for the two jewels high to the south in the pre-dawn sky. Saturn passes a milestone this week on Wednesday the 6th, when it ceases its normal easterly movement against the stars and begins retrograde (westerly) movement as a result of the faster Earth preparing to pass between it and the Sun. Over the next several weeks, watch the planet move slowly away from Regulus rather than toward it. Periodic retrograde motions of the planets were the first real clues that the planets orbit around the Sun rather than around the Earth.

Cetus, the Whale or Sea Monster, holds forth in the mid-evening sky. Look for bright Fomalhaut well to the southwest around 8 PM, and then up and to the left to find Cetus's brightest star, Deneb Kaitos. The rest of the constellation sprawls further up and to the left, ending in an irregular circle that makes the Whale's head. To the north lie the triangles of stars that make Aries, the Ram, and Triangulum, the Triangle.
Valid HTML 4.0!