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The Sky This Week, 2012 May 22 - 29

Venus plunges, Mars coasts, Saturn delights, and the Moon returns.
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Partial Eclipse Shadows on the wall of the Flagstaff Station
Imaged 2012 May 20 by USNO Astronomer Merri Sue Carter

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Venus (lower right) and Gemini over Mulberry Creek, Morattico, Virginia, 2012 May 19
Imaged with a Canon EOS Rebel T2i DSLR, 20s @ f/5.6, ISO 1600


The Moon returns to the evening sky this week, climbing past plunging Venus and ruddy Mars as the week progresses. First Quarter occurs on the 28th at 4:16 pm Eastern Daylight Time. Look for Luna’s last evening encounter with bright Venus this year in the fading twilight of the 22nd. On the night of the 25th the Moon forms the end of a line with the Twin Stars of Gemini, Castor and Pollux. On the 27th she passes seven degrees south of the bright star Regulus in Leo, and on the 28th lies a similar distance south of Mars.

Last week’s annular eclipse of the Sun was widely observed by many people in the western U.S. By a stroke of good fortune the central path passed over several national parks where thousands of people waited in anticipation for it. Those who saw it were enthralled by the dazzling ring of sunlight surrounding the dark disc of the Moon, and many people had a chance to take some very creative images of the event. We’ll have to wait until 2017 August 21st for the next central solar eclipse to touch American shores, but that one will be a spectacular total eclipse that will be well worth the wait.

Anticipation is now building for the Transit of Venus that will take place on June 5th. You can still see Venus in the evening sky as the week opens, but she is now falling toward the western horizon like a stone, setting nearly seven minutes earlier with each successive night. By the end of the week she sets less than an hour after the Sun. It’s during these last weeks of any evening apparition of Venus that the planet puts on its best show for the small telescope. As the planet approaches the Earth before passing between us and the Sun its disc grows ever larger and its crescent becomes ever slimmer. You can easily see the slender phase in a pair of binoculars, and some exceptionally keen-eyed people can see the crescent with the unaided eye. This is the week to look for a very elusive phenomenon called the "Ashen Light". This soft glow is best seen in deep twilight and appears as a very subtle brightening of the unlit portion of Venus’ disc, similar to "Earthshine" on the waxing lunar crescent. The cause of the glow is still a mystery, but it may originate from sunlight scattering through Venus’ dense atmosphere or heat from the planet’s hellish surface stimulating "airglow" far above the ground. As the crescent gets thinner the light seems to become easier to see, but you’ll need to have an exceptionally clear sky to hope to glimpse it.

Mars is picking up speed as he moves eastward through the stars of Leo, the Lion. The red planet will continue to trudge around the zodiacal constellations through the rest of the year, gradually growing fainter in the process. His disc will still show hints of detail in large telescopes under steady air, but in modest instruments he’ll be little more than a pale pink dot.

Saturn emerges from evening twilight high up in the southeastern sky, so you’ll have something to point the telescope to after Venus departs for the night. Saturn always pleases the folks who look at it for the first or the hundredth time! If you’re having a neighborhood cook-out over the coming holiday weekend, bring your telescope along and become the toast of your block!

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