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The Sky This Week, 2012 May 8 - 15

Lions and planets and bears, oh my!


Venus, 2012 April 25, 21:22 UT
Imaged from Alexandria, VA with a 3.1-inch (80mm) f/6 refractor,
1.6X Barlow lens, and a Canon EOS Rebel T2i DSLR

The Moon wanes in the morning sky this week, with Last Quarter falling on the 12th at 5:47 pm Eastern Daylight Time. Luna begins the week perched above the "teapot" asterism of Sagittarius. From there she sails majestically through the faint "water" constellations of the autumnal sky, Capricornus, Aquarius, and Pisces. It will be a lonely voyage since there are no bright objects to meet up with along her celestial path.

As darker skies once again take over the evening sky it’s a great time to become acquainted with the constellations of late spring. The last of the bright stars of the Great Winter Circle now wallow in the west, having done their part to light up the long dark nights of that season. The stars of spring are more subtle, but two easily-recognized patterns now straddle the meridian as evening twilight fades. High overhead in the north are seven stars that almost everyone who lives in the Northern Hemisphere will recognize. Shaped roughly like a box with a long handle, these stars form the asterism we call the Big Dipper. They are part of the much larger constellation of Ursa Major, the Great Bear. The four stars of the Dipper’s "bowl" mark the Bear’s haunches, while the three "handle" stars define a rather un-ursine tail. From a dark-sky location you can trace out legs, claws, and a head from the many third- and fourth-magnitude stars that are normally masked by moonlight or city glow. Turning to face the south you’ll find another great celestial beast, Leo the Lion. This year Leo is hosting Mars, which lies just under 10 degrees east of Leo’s brightest star, Regulus. Above Regulus you’ll find five fainter stars which trace out a figure resembling a sickle or a backwards question mark. These form the Lion’s head. Ten degrees east and a little north of Mars is a right triangle which traces the Lion’s hindquarters. These two great predators patrol the spring sky foraging for their offspring, which are nearby in the forms of the obscure constellations of Ursa Minor and Leo Minor.

In the east you’ll notice a bright rose-tinted star following the Bear and the Lion. This is Arcturus, the brightest star in the northern sky and third-brightest overall. Follow the arc made by the Big Dipper’s handle to "arc to Arcturus", then continue that line to "speed on to Spica", the blue-tinted lead star of Virgo which is enjoying the company of Saturn at the moment. If you have a telescope and a dark-sky site, explore the area of the sky bounded by the Big Dipper, Leo, Arcturus, and Spica. You’ll notice dozens of faint smudges of amorphous light in these areas, the soft tell-tale glimmer of distant galaxies. Dubbed "the Realm of the Nebulae" by 19th Century observers, this part of the sky contains thousands of galaxies belonging to a vast cluster, to which our Milky Way belongs as a far-flung outsider.

Dazzling Venus spends the week seemingly hanging close to the second-magnitude star Al Nath in the constellation of Taurus, the Bull. The brilliant planet is now beginning to catch up to the Earth in the great orbital steeplechase, and over the next few weeks she will drop from the evening sky like a stone.

Mars continues to accelerate eastwards among the stars of Leo. He is well-placed for viewing on the meridian at the end of evening twilight, but his disc is shrinking rapidly as Earth pulls away from him. You’ll need a telescope of at least eight inches aperture to glean much detail from his shrinking surface.

Where Mars challenges planetary observers, Saturn delights. The ringed planet is still rising as darkness falls, so you have many hours to enjoy what I consider to be the most exotic object in our solar system. In a medium-aperture telescope under a dark sky the planet with its mysterious appendages seems to swim among half a dozen faint icy satellites and one large and very exotic moon, Titan. Saturn, its rings and moons are continuing to provide surprising discoveries for the Cassini mission, which is now in its eight year of exploring this far-flung planetary system.

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