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The Sky This Week, 2017 February 28 - March 7

Keeping watch on the Moon.
The Moon, imaged 2017 February 3 with USNO's 30.5-cm (12-inch) f/15
Clark/Saegmüller refractor

and a Canon EOS Rebel T2i DSLR

The Moon climbs into the evening sky this week, waxing through her crescent phases to First Quarter, which occurs on March 5th at 6:32 am Eastern Standard Time. You’ll find the young crescent about 10 degrees southeast of brilliant Venus during evening twilight on the 28th. On the following night she welcomes March from a perch just four degrees south of ruddy Mars. If you have binoculars of a small telescope you can spend the evening watching Luna drift through the Hyades star cluster. Along the way she will occult several of the cluster’s stars. At 11:04 pm she will hide the bright star Aldebaran for just over half an hour. Aldebaran will emerge from the Moon’s bright limb at 11:39 pm.

The Moon herself is the best telescopic target in the evening sky. The phases that flank First Quarter offer some of the most interesting sights for owners of telescopes of just about any size. As the terminator slowly crawls across the Moon’s face from night to night prominent craters, vast lava plains, and great chains of mountain peaks come into view, and gradually change their appearance as the local lighting from the Sun climbs higher in the lunar sky. This is also the time of year when the nights around First Quarter show the Moon at her highest declination in the northern sky, so you’re looking through the least amount of our atmospheric turbulence when you gaze at her stark airless surface. While the Moon’s surface often seems close enough to touch on nights of steady "seeing", it’s still very hard to grasp the scale of her surface features. Even with our 12-inch refractor telescope here at the Naval Observatory the smallest features we can see under the best conditions are just under a kilometer across. To put that into perspective, if the famous Meteor Crater in Arizona were relocated to the Moon it would just be visible in that great telescope under the best conditions!

As Luna climbs to the apex of her path around the sky she casts more and more light, gradually swallowing the view of the fainter stars. Fortunately the Moon’s path takes her through the middle of the Great Winter Circle, so the bright outlines of Orion and his surrounding companions can still be seen despite the increasing glare of our only natural satellite. When you tire of looking at Luna’s battered surface, turn your telescope toward the bright stars of the Great Winter Circle and enjoy their subtle differences in brightness and color.

Dazzling Venus, which has dominated the view in the western early evening sky since last autumn, is poised to make a dramatic exit from the sky. Right now she is well-placed in the west as the Sun sets, popping into view just after the Sun goes down. She lingers until well after the end of evening twilight, but in less than a month she will pass between the Earth and the Sun, then vault into the morning sky. You’ll notice the beginning of this plunge from the sky this week; by the week’s end she will set five minutes earlier each successive night. However, there is a positive side to this if you won a telescope. Over the course of the next few weeks her apparent disc will grow in size as she becomes an ever-slimming crescent. You should be able to spot her phase in a pair of steadily-held binoculars.

Mars continues to keep pace ahead of the Sun, losing just a few minutes of visibility over the course of March. The red planet moves from the constellation of Pisces into Aires, the Ram. After Venus he is still the brightest object in the western sky at the end of evening twilight, and his characteristic pinkish glow should easily identify him.

Giant Jupiter now rises at around 9:00 pm, making steady progress toward better visibility in the evening sky. He will come to opposition in early April, but if you can’t wait until them to get him in your sights you can now get a good view of him by midnight. He is located just above the first-magnitude star Spica, and he will remain near the star during the majority of his 2017 apparition.

Saturn can be found low in the southeastern sky in the gathering morning twilight. The ringed planet is located just over 15 degrees east of the ruddy star Antares, which crosses the meridian at around 6:00 am EST.

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