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The Sky This Week, 2016 April 5 - 12

Celebrating dark skies and bright planets
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Jupiter, imaged on 2016 April 4 at 02:29 UT

The Moon returns to the evening sky this week, with New Moon falling on the 7th at 7:24 am Eastern Daylight Time. Try to find the slender crescent Moon low in the west on the evening of the 8th. On the 10th you’ll find Luna less than half a degree from the bright star Aldebaran in the constellation of Taurus, the Bull as twilight ends. If you live in the eastern U.S. and have a telescope, you can watch Aldebaran slip behind Luna’s dark limb at 6:44 pm EDT and re-appear on the bright limp at 7:56 pm.

This week has been designated as "Dark Sky Week" by the International Dark Sky Association. It’s a week set aside each year to raise awareness about light pollution and the effects of poor nighttime lighting on the environment. The IDA has been a leading institution in studying the economic and environmental effects of outdoor lighting for 35 years by raising awareness of the disappearing night sky. One of the activities for the week is the Globe at Night citizen science program, which continues until the 10th. Simply compare your views of the stars of Leo, the Lion, to star charts on the website to gauge the brightness of your particular patch of sky. The effort to modify our outdoor lighting habits has many benefits, as studies have shown how our use of lighting has important implications on our circadian rhythms and general health. Poor outdoor lighting also affects many nocturnal animals and wastes energy and taxpayer money. Take some time this week to consider the night sky and the wonderful resource that it truly is.

During evening twilight this week you’ll have the year’s best chance to see the elusive planet Mercury grace the darkening sky. The fleet planet may be found low in the west throughout the week, climbing higher above the horizon on each successive night. On the evening of the 8th you’ll find Mercury about seven degrees below and to the right of the slender crescent Moon. You should have little trouble spotting him about 45 minutes after sunset so long as you have a flat western horizon. He’ll hang around for the next few weeks, but he’ll gradually fade during that time.

Jupiter continues to be the dominant planet in the evening sky. Old Jove now shines brightly throughout the evening hours, crossing the meridian at around 11:00 pm. You should be able to find him high in the southeast shortly after sunset, and he will be well-placed for telescopic observation as soon as you spot him. It’s hard to put into words the superlatives that Jupiter represents. It is the largest planet in the solar system, with a diameter some 10 times larger than Earth and a volume that could easily contain 1100 Earth-sized planets. The dark equatorial cloud belts, visible in almost any telescope, are produced by a ferocious "jet stream" in the planet’s atmosphere where winds approach the speed of sound. The famous Great Red Spot is a long-lived storm system in the South Equatorial Belt that has persisted for over 300 years and covers an area comparable to the entire surface area of our home planet. Jupiter also carries over 60 moons in tow. The largest of these, the Galilean moons, were first described by Galileo over 400 years ago and remain as fascinating to us as they did to him. Despite its great distance from Earth, currently some 420 million miles, an amazing amount of detail can be glimpsed with relatively modest telescopes. No wonder amateur astronomers spend so much time looking at him!

Mars and Saturn now rise at around midnight, but the best time to give them a look is still before dawn in the southern sky. They are both located near the bright star Antares in the constellation of Scorpius near the southernmost reaches of the Ecliptic. This makes them rather difficult to observe, since their proximity to the horizon means their light mist pass through denser layers of our atmosphere. Still, they can be rewarding targets when conditions allow. Saturn’s rings can be seen in any telescope, but to catch details on the red planet you’ll need a telescope with at least four inches of aperture.

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