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The Sky This Week, 2013 July 16 - 23

Exploring worlds near and far
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Saturn with three moons, 2013 July 15, 01:40 UT 


The Moon skirts the southern horizon this week, gradually turning northward as she enters the faint star-fields of the autumn constellations. Full Moon occurs on the 22nd at 2:16 pm Eastern Daylight Time. July’s Full Moon is popularly known as the Buck Moon, and if you see any of the deer here at the Observatory it’s easy to see why it gets that name. This is the time of year when bucks’ antlers fully develop in preparation for sparring contests in the fall. It is also known as the Thunder Moon because of the frequency of diurnal storms on hot July afternoons. This week the Moon begins her course just below the planet Saturn. On the evening of the 18th she may be found just east of the second-magnitude star Graffias, northernmost star in the "head" of Scorpius. The Scorpion’s ruddy heart, marked by the star Antares, will be seven degrees to the southeast. The Full Moon on the 22nd will be just a degree east of the third-magnitude star Dabih in the constellation of Capricornus, but the star may be overwhelmed by Luna’s bright glare.

It is hard to believe that 44 years ago the first footprints left by humans on another world were left on the dusty desolation of the Moon’s Sea of Tranquility. On July 20, 1969 Neil Armstrong and Edwin "Buzz" Aldrin became the first people to tread the surface of another world. Take a few moments on the evening of the 20th to reflect on this achievement and to honor the memory of Mr. Armstrong, who passed away last year. If you have a small telescope, take a look at our nearest neighbor in space and marvel at the battered landscapes that will greet you in the eyepiece.

Evening twilight finds Venus glimmering brightly in the western sky. The dazzling planet is moving along the ecliptic with a pace that’s slightly faster than the Sun. This puts her in an interesting situation. If you watch her very carefully you’ll notice that she sets about a minute earlier each evening; however the Sun also sets about a minute earlier as well, so Venus maintains the same relative distance from Old Sol. In another few weeks the Sun’s pace will begin to lag behind Venus and she will finally set after the end of evening twilight. Look for Venus close to the bright star Regulus on the evenings of the 21st and 22nd.

Saturn is now well west of the meridian as twilight begins to darken the sky. From my observing site at home I find that I only have about an hour to get the telescope on him before he disappears behind neighborhood trees. However, from an open-sky site you’ll have a bit more time to enjoy this distant, curious world. Despite the planet’s southerly declination, the heat and humid conditions of late actually help improve the view of his subtle cloud belts and tantalizing rings. The reason for this is that summer heat waves usually involve a stagnant dome of high-pressure air over the DC area, and this limits the effects of jet streams in the Earth’s upper atmosphere overhead. Curiously, this actually allows us to better view the bright equatorial cloud belt on Saturn, which boasts one of the strongest jet streams in the solar system. Winds here blow in excess of 1000 miles per hour! On the 19th, be sure to take a few minutes to look at the planet. On this date the Cassini spacecraft that’s been orbiting Saturn since 2004 will take a picture looking back toward the Earth; be sure to wave and smile!

Early risers will have a treat to look for in the pre-dawn sky in addition to the coolest temperatures of the day. Two planets will come together in the gathering twilight for one of the closest planetary conjunctions of the year. The planets in question are Mars and Jupiter, which you will find about 10 degrees up in the east-northeast about 45 minutes before sunrise. Jupiter should be easy to spot with the naked eye, but you may wish to use binoculars to help locate ruddy Mars. The planets will be close for a day or two before and after the 22nd, but that morning they will be just ¾ of a degree apart. Both objects will be prominent in the evening skies in 2014, with Jupiter dominating the winter night and Mars holding court in the spring.

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