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The Sky This Week, 2016 April 12 - 19

Celebrate Yuri's Night!
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The Crescent Moon & Mercury, 2016 April 8
Imaged from the dome of the USNO's 12-inch telescope

The Moon waxes in the evening sky this week, brightening the stars of the winter and springtime constellations. First Quarter occurs on the 13th at 11:59 pm Eastern daylight Time. Luna will pass just over a degree north of the second-magnitude star Alhena on the evening of the 12th. On the 16th you’ll find her three degrees south of the first-magnitude star Regulus. On the following night she passes just two degrees south of bright Jupiter.

April 12th is widely observed by amateur astronomers and space enthusiasts around the world as "Yuri’s Night". It was on this date in 1961 that Yuri Gagarin became the first human to enter space. It was also the date of the first flight of the Space Shuttle, when the orbiter "Columbia" lifted off in 1981. This is a great night to share your astronomical interests with your friends, family, and neighbors. If you have a telescope, set it up in your yard and invite everyone for a look at the Moon and Jupiter. You’ll be joining a cadre of thousands of amateur astronomers around the world providing glimpses of past and future destinations in space. This is also a good time to talk about artificial night lighting and its role in reducing our view of the sky. It’s a great opportunity to act locally and think globally.

The elusive planet Mercury is now approaching his greatest elongation east of the Sun, which occurs on the 17th. This will be the best evening show of the year for the solar system’s innermost world, which is never particularly easy to see. You’ll need a good open western horizon and clear skies, but with a little luck you should be able to track him down. Go out about half an hour after sunset and look to the west. You’ll find Mercury about 10 degrees above the horizon, glimmering with a pale orange glow. Early in the week he’ll shine brighter than any star in the sky except Sirius. As the week passes he’ll climb a little bit higher each night, but his light will slowly fade. He sets around the end of evening twilight all week long, so you should have adequate time to find him. Later in the week binoculars may be helpful, but once you’ve located him he should be relatively easy to find on successive nights.

Jupiter gets a visit from the Moon on the evening of the 17th, but you won’t need the moon to identify him in the evening sky. After the Sun and Moon Old Jove is the brightest object in the sky, and he becomes visible high in the southeast shortly after sunset. He’s ideally placed for viewing all evening long, crossing the meridian at around 10:30 pm. You can follow the night-to-night antics of his four bright Galilean moons with any telescope, and if you have a telescope of modest aperture you can see details in his turbulent atmosphere. On the evening of the 15th look for the planet’s famous Great Red Spot to rotate across his disc while the moon Io drags its shadow across the distant cloud tops.

Early risers can still enjoy the gathering of the planets Mars and Saturn near the bright star Antares in the constellation of Scorpius. The trio is best seen at around 5:00 am when they are near the meridian, but you can still get a good look at them in morning twilight about an hour later. Mars will reach the first stationary point in his apparition on the 17th. He’ll stop his eastward motion along the ecliptic at this time and begin retrograding westward for the next couple of months.

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