The Sky This Week : September 10 thru 17, 2013 !

The Sky This Week, 2013 September 10 – 17
A great week to view the Moon!
Coper-Erat_121123_02small.jpg

Lunar craters Copernicus (left) and Eratosthenes
Imaged 2012 November 23

The Moon skirts the southern horizon this week, waxing to a fat gibbous phase as she moves through late summer’s constellations and into the autumnal sky. First quarter occurs on the 12th at 1:08 pm Eastern Daylight Time. She passes several degrees north of the bright star Antares on the evening of the 11th, then drifts through the heart of the summer Milky Way over the next two nights passing above the “teapot” asterism of Sagittarius on the night of the 13th. From there she will drift through the sparser starfields of Capricornus and Aquarius.

The Moon fills a prominent gap in the sky for owners of small telescopes. The early evening’s two bright planets are gone by the end of evening twilight and Jupiter doesn’t rise until the wee hours. Despite her low altitude, Luna waxes through her best phases for visual exploration, starting the week as a fat crescent and ending in a gibbous. From night to night you can watch the “terminator” line creep across the lunar landscape, revealing a new set of cratered vistas for each evening’s expeditions. Even though her features are essentially permanent, I always enjoy visiting old familiar landmarks. Subtle changes in illumination from lunation to lunation often reveal details that I’ve overlooked or never noticed in the past. One of my favorite parts of the Moon to study is the area between the prominent craters Copernicus and Eratosthenes, on the southern edge of the great impact basin called mare Imbrium. These craters will be on the terminator on the nights of the 13th and 14th. Between them is a field of dozens of small “secondary” impact craters caused by the debris from the impact that created Copernicus that rained down on the surrounding landscape. They bear a mute testimony to the force of the blast that created the crater, especially when you realize that the diameter of Copernicus is almost twice the distance from Washington, DC to Baltimore!

Despite their low altitude and poor telescopic visibility, you should still take a few minutes in the early evening to watch Venus and Saturn in the southwestern twilight sky. Dazzling Venus will catch up to the much dimmer glow of Saturn and pass just three degrees south of the ringed planet on the evenings of the 16th and 17th. Both planets will set at the end of evening twilight, but Venus will slowly gain ground on the advancing Sun and gradually become more prominent in the late autumn and early winter. Saturn, alas, will steadily fall toward the Sun’s glare over the next several weeks, becoming increasingly difficult to spot. We’ll have to wait until next spring to see him grace the evening skies again.

Jupiter is still best seen in the early morning hours, but he’s making steady progress towards an appearance in the evening sky. Old Jove now rises at around 1:30 am EDT and may be found high in the east as morning twilight starts to brighten the horizon. As we enter the last few weeks of daylight time it would be worthwhile to grab a few early morning peeks at the giant planet for a preview of things to come when he reaches opposition in January. His roiling cloud belts are putting on a good show and the famous Great Red Spot is more prominent than it has been for many years.

Mars may be found about halfway between Jupiter and the eastern horizon before dawn. The red planet is now located about halfway between the Twin Stars of Gemini, Castor and Pollux, and Regulus, the heart of Leo, the Lion. If you have binoculars you can watch Mars pull away from the scattered star cluster known as the Beehive in the dim constellation of cancer, the Crab. Mars will continue his eastward trek against the background stars, taking aim at Regulus. He will continue to travel eastward into the sprawling constellation of Virgo by the springtime, reaching opposition near the bright star Spica in early April.

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