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The Sky This Week, 2010 July 27 - August 3

Planetary "leapfrog", and the joys of summer stargazing

 Summer Stargazing at its best
The Race, Fishers Island, NY, August 2006

The Moon wanes in the late night and early morning sky this week, spending most of her time among the faint stars of the rising autumnal constellations.  Last Quarter occurs on August 3rd at 12:59 am Eastern Daylight Time.  Luna does pay a call on one bright object this week as she glides some six degrees north of giant Jupiter during the morning hours of the 31st.  By the week’s end the crescent Moon is closing in on the famous Pleiades star cluster.  

As Luna drifts into the morning sky, the stars of summer once again have an opportunity to shine.  Many of us take advantage of August as the time for a summer vacation, and going to the seashore or the mountains offers an opportunity to escape the haze and light pollution that surrounds our urban and suburban enclaves.  It’s also the time of year to see one of the most wonderful sights in all of Nature, the magnificent panorama of the summer Milky Way.  Our home Galaxy can be appreciated on many levels, with and without optical aid.  The wonderful sweep of its misty glimmer is often best appreciated by simply lying on your back in an open space such as a meadow or beach and simply looking up.  As your eyes become accustomed to the dark, subtle details in the Milky Way reveal themselves in the form of knots of nebulous light and patches of seeming emptiness.  In the hours after sunset and before sunrise the occasional satellite drifts through the field, a not-so-subtle reminder of our activity in space.  Hoist a pair of binoculars and the nebulous patches of the Galaxy become clouds of innumerable faint stars interspersed with knots of glowing gas and star clusters.  Point a telescope at these objects and watch them resolve into intricate tracings of delicate nebulosity or groupings of dozens to hundreds of stars.  From very dark locations the familiar outlines of many constellations become lost in an ocean of background stars and the sky itself seems to glow with a faint, suffused light.  Yes, summer stargazing is at its best as July turns to August.  Stay up late a few nights while you’re away!  

As you wait for the sky to darken in the hours after sunset, keep an eye on the southwestern sky, where three planets are participating in one of the best series of conjunctions for the year.  The objects in question are Venus, Mars, and Saturn, and they will spend the next couple of weeks playing a celestial version of “leapfrog” during the twilight hours.  As the week opens, both Venus and Mars lie to the west of Saturn.  By the end of July Mars overtakes and passes the more distant ringed planet, with closest approach between the duo falling on the evening of the 31st.  In the meantime, dazzling Venus is chasing down both objects, and by the end of the week you’ll see an attractive triangle in the southwest with Mars and Venus forming the base and Saturn the apex.  Looking ahead to August, Venus blows by Saturn on the 7th, then passes Mars on the 18th.    

All of this activity in the early evening sky sets the stage for the entrance of Jupiter, who rises just as Saturn and his companions set.  By the end of the week you should see Old Jove in the east at around 11:00 pm, and by midnight he should be high enough to train the telescope in his direction.  Jupiter will become an easier target as August passes, rising about four minutes earlier each night.  He’s still missing his prominent South Equatorial Belt of dark clouds, but this in turn helps to accentuate the famous Great Red Spot, which is the planet’s most famous feature. 

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