Sunday, May 10, 2009

May 10th-16th: This Weeks Sky Highlights

May 10th
Look for Luna rising with ruddy Antares, heart of Scorpius, the Scorpion, late in the evening of the 10th. Luna washes out all but the brightest stars this week, but there are a number of interesting things to look for despite her glare. This is the time of the year when we see one of the oldest dramas in skylore play out during the late evening hours. If you head out about an hour after sunset and look toward the west, you’ll see the flickering light of the sky’s brightest star, Sirius, dancing just above the trees.

High in the south at the end of evening twilight is where you’ll find Saturn, now the lone bright planet visible in the evening sky. He’s perched under the right triangle of stars that make up the hindquarters of Leo, the Lion. Since the start of the year the ringed planet has been slowly progressing westward against the background stars. This "retrograde" motion will come to an end by early next week. The planet’s rings have also been slowly opening toward our line of sight, but they reach their extreme for the year this week, tilting just over five degrees. They will slowly begin to close up for the rest of the current apparition, going "edge-on" to us in early September.

Venus and Mars are engaged in an extended game of "cat and mouse" this week. You should be able to easily spot Venus some 45 minutes before sunrise along the eastern horizon. Mars will be more of a challenge, though, and you'll probably need binoculars to see him. The two planets are moving eastward against the stars at nearly identical rates, so all week long Mars maintains a six degree lead on the brighter Venus.

Vega is the summertime equal of Arcturus which is a bright winter star. Vega is already making its way up in the northeast after dark. It is the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. It's 25 light-years distant and lies in the constellation Lyra. Four stars form the main "body" of the Lyre: Beta, Gamma, Delta and Zeta Lyrae. Together they make a kind parallelogram. At the northwestern corner of this parallelogram a triangle of stars can be seen: Alpha (Vega), Epsilon and again Zeta Lyrae. Within this constellation lies the most famous planetary nebula in the sky, M 57 or the Ring Nebula.

Face north at nightfall this week and look very high, almost overhead. There's the Big Dipper, floating upside down. The middle star of its bent handle is Mizar; can you see tiny Alcor hiding in its skirts? To find out on which side of Mizar to look for Alcor, notice that Vega is rising way off in the northeast. A line from Mizar through Alcor always points to Vega.

May 15th
By 11 p.m. the Moon is well up in the southeast. Look to its lower left, by a bit less than a fist-width at arm's length, for reddish, summery Antares already on the rise. Scattered nearby are fainter stars of Scorpius. Due to its location on the Milky Way, this constellation contains many deep sky objects such as the open clusters Messier 6 (the Butterfly Cluster) and Messier 7 (the Ptolemy Cluster), and the globular clusters Messier 4 and Messier 80.

This is the time of year when the Gemini twins stand upright in the west as twilight fades. Their bright head stars, Pollux and Castor, are lined up nearly horizontally just 4½° apart, about the width of three fingers at arm's length. Castor is the brighter of the two, and was discovered to be a visual binary in 1678. Each of the components of Castor is itself a spectroscopic binary, making Castor a quadruple star system.

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