The Sky This Week, 2012 July 10 - 17
Saturn, imaged 2012 June 17, 02:08 UT
The Moon wanes in the pre-dawn sky this week, passing through her crescent phases before becoming lost in the glow of twilight. New Moon occurs on the 19th at 12:24 am Eastern Daylight Time. She drifts out of the star-poor constellations of late autumn and ends the week cavorting in the rising stars of the Great Winter Circle. From the 14th through the 16th she flirts with the bright planets Venus and Jupiter just before dawn, and on the morning of the 15th the Moon, Venus, Jupiter, and the bright star Aldebaran will gather for one of the most spectacular conjunctions for the year. Even though it’s a Sunday morning, this one will be worth getting up early to see!
With the Moon lurking in the early morning sky we now have an opportunity to enjoy the splendor of summer’s more distant celestial sights. This is the time of year when many of us are on vacation, and often our journeys take us away from cities to the mountains or the shore. In many cases you’re a good distance from city lights, and the more subtle lights of the night sky have much more prominence. It’s a great time of year for casual stargazing, since there’s plenty of time for social activity in the evening before the sky fully darkens, and you have several hours of viewing time before the first rays of dawn send you to bed in the wee hours. If you start observing at around 10:30 pm you will see the summer equivalent to winter’s Orion hovering over the southern horizon. Like Orion, this constellation is marked by a bright reddish star called Antares, which means "Rival of Mars". Also like Orion, this reddish star is surrounded by a striking pattern of blue stars that form a very good representation of a Scorpion. The constellation of Scorpius is even related to Orion in mythology, with the lowly creature causing the death of the mighty hunter in a fit of Greek goddess jealousy. Both Orion and Scorpius were placed in the sky by the gods, but they never appear together at the same time!
By midnight the heart of the summertime Milky Way stands above the southern horizon, a vast glowing mass of soft starlight. It seems to originate from the "spout" of a teapot-shaped asterism that’s formed by the brighter stars of the constellation Sagittarius, the Archer. Gazing in this direction would give us a view of the heart of our home Galaxy were it not for the vast clouds of dust, gas, and stars that veil the enigmatic center. If we could "see" with x-ray "eyes", we would detect one of the brightest sources of high-energy radiation in the sky, the black hole that resides in the Milky Way’s core and lurks some 30,000 light years from us. Our visually attuned eyes can trace the Milky Way back up to the northeast, where it passes through the bright stars of the Summer Triangle, Vega, Deneb, and Altair.
The early evening hours offer us a chance to sight two planets that are trying to outpace the advancing Sun. Mars and Saturn are both located in the constellation Virgo, and it won’t take you too long to figure out who the favorite will be in this race. Mars is rapidly closing in on Saturn, and if you want to measure his progress just watch him move against some of Virgo’s brighter stars this week. This week the red planet zooms by the star Eta Virginis, passing just over a degree south of the star on the evenings of the 12th and 13th. By the end of the week he’ll form a nice triangle with Eta and Gamma Virginis.
Saturn still lingers about five degrees north of Virgo’s brightest star Spica. Although he has resumed direct eastward motion, it will take him about two weeks to cover the distance that Mars moves in one night. You still have a few hours to enjoy viewing the ringed planet through the telescope before he drops into the horizon haze, but the best time to look at him is in late evening twilight when he’s still well up in the southwest.
As mentioned earlier, Jupiter and Venus are dazzling early risers and will continue to do so through the course of the month. Once the Moon passes them, though, the distance between them will begin to grow. Venus passes one degree north of the bright star Aldebaran on the morning of the 11th, and by the 15th the Moon and Jupiter will help to form an almost perfect parallelogram with Venus and the star. It should be quite a show!