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The Sky This Week, 2011 May 24 - 31

Strung-out planets in the morning sky, spring's easy star patterns
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Saturn and its large moon Titan, 2011 May 12, 02:27 UT


The Moon wanes through her crescent phases in the early morning sky this week. New Moon occurs on June 1st at 5:03 pm Eastern Daylight Time. Luna spends most of the week drifting through the dim starfields of the autumnal constellations, but as the week ends she encounters the bevy of planets that are still visible in the gathering morning twilight. Look for the Moon just over four degrees north of bright Jupiter on the morning of the 29th. On the 30th look for her about eight degrees northwest of bright Venus about 20 minutes before sunrise. Venus will be just five degrees above the horizon, but with a clear sky and an open view to the east you should be able to track her down in the brightening sky. About halfway between Venus and the Moon use a pair of binoculars to try to snag a glimpse of ruddy Mars gradually emerging from the solar glare.

The overnight hours are now dominated by a relatively few bright objects and a couple of recognizable star patterns. The rose-tinted star Arcturus is the brightest of this lot, shining down from a perch high overhead in the south as astronomical evening twilight ends. The brightest star in the northern hemisphere sky, it is over a full magnitude brighter than the spring’s other first-magnitude luminaries, Spica and Regulus. The latter star may be found in the southwestern sky as twilight ends, and it is the brightest star in the constellation of Leo, the Lion. Leo is one of the very few constellations that doesn’t require a huge leap of imagination to trace out. With Regulus marking the Lion’s heart, look above the bright star for a sickle-shaped asterism that outlines Leo’s head. 16 degrees to the east is a right triangle of stars marking the Lion’s haunches, with the second-magnitude star Denebola staking the tip of the beast’s tail. In a dark sky you can trace out more stars underneath the main figure and arrange them in imaginary chains to depict his legs. Almost at the zenith at this hour is another well-known asterism of seven stars that’s popularly known here in America as the "Big Dipper" and in England as "The Plough". While none of the stars in this group are particularly bright, it is an easy pattern to trace out even in the light-polluted skies of the city. Farther afield the fainter outlier stars reveal a fairly acceptable outline that has some resemblance to a bear, except for the long "tail" that’s formed by the Dipper’s "handle". These fainter stars of Ursa Major extend about the length of the Dipper to the east and south, where keen eye-d skywatchers can imagine four legs and a chunky head leading the brighter stars around the sky.

The second-brightest object in the evening sky after Arcturus if the ringed planet Saturn. The planet’s yellow tint stands out well in contrast to the blue hue of nearby Spica and the rosier glow of Arcturus. Through the telescope the shadow of the planet’s globe on the famous rings is becoming very easy to see as Saturn moves toward quadrature. If you happen to catch a night of very steady seeing while you observe the ringed planet, swing your telescope just half a degree to the west to the third-magnitude star known as Porrima. This star is a very famous double star that is often used as a test for premium telescope optics. It is one of the few doubles in the sky which shows appreciable change in the separation and position angle of its component from year to year. The pair is now opening up from a very close periastron several years ago. At that time I couldn’t split the components with my 8-inch telescope, but now they are once again visible as two distinct stars.

Mercury, Venus, Mars and Jupiter are now breaking up their scrum in the pre-dawn sky. Mercury is now lost in the solar glare of morning twilight, but Venus and Jupiter should still be fairly easy to spot about 20 minutes before sunrise. As mentioned earlier, use the Moon and Venus to try to track down dim ruddy Mars on the 30th. The red planet will gradually become more visible over the next several months, but if you want to get an early start on this year’s apparition this is a good chance to get a little help from some bright friends.

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