The Sky This Week, 2013 July 2 - 9
Globular Cluster Messier 13 in Hercules
The Moon may be found in the pre-dawn sky this week, waning to a thin crescent before disappearing in the rising SunÆs glare. New Moon occurs on the 8th at 3:14 am Eastern Daylight Time. Early risers on the 4th will find Luna some five degrees south of the rising Pleiades star cluster. The next morning she passes just three degrees northeast of the bright star Aldebaran. If youÆre up for an early morning challenge and have a clear horizon to the east, try to locate the MoonÆs sliver of a crescent just before sunrise. If you have a pair of binoculars, look just above the Moon for the reddish glimmer of Mars. The red planet is gradually emerging from solar conjunction, and in another few weeks will be a bit higher and easier to spot.
Earth passes aphelion, its most distant point from the Sun, on the 5th at 10:44 am EDT. At this time weÆll be 152,097,413 kilometers (94,508,951 miles) from Old Sol. Since weÆre at our most distant from the day-star weÆre moving at our slowest orbital velocity for the year. This causes the Northern Hemisphere summer season to last a bit longer than the other three. That may be a small consolation to think about once weÆre in the grip of winter!
If the sky ever clears this will be a great week to get out and observe the ôdeep-skyö. This term is what I use to describe everything thatÆs beyond our solar system and the nearby stars that form the constellation patterns. Deep-sky encompasses the Milky Way and the myriad of star clusters, nebulae, and external galaxies that are available for enjoyment with small telescopes. The summer deep-sky is dominated by the massive star clouds of the central parts of our Milky Way galaxy. From a dark location this diffuse band of light arches across the midnight sky with its densest regions hovering over the southern horizon. Binoculars or small, wide-field telescopes are the best tools for exploring these regions, especially the fields above the stars of Scorpius and Sagittarius. As you sweep upward toward the bright stars of the Summer Triangle, youÆll encounter dark rifts of starlessness interspersed with the knots of star clusters and glowing nebulae.
A characteristic object in this part of the sky is the ôglobular clusterö. These hazy puff-balls of light are clusters of hundreds of thousands of very old stars that slowly orbit the Milky WayÆs center, taking a few hundred million years to complete one circuit. There are some 150 such clusters in the Milky WayÆs system, and some of the best and brightest are showcased right now. The best of these is Messier 13, the Great Hercules Cluster, which can be seen in binoculars as a hazy patch nestled between two 7th magnitude stars in the northwest corner of the ôKeystoneö asterism in Hercules. A 4-inch telescope will show a smattering of tiny stellar pinpoints surrounding a bright fuzzy core, and in instruments with 8 or more inches of aperture it resolves into a swarm of uncountable stars. Messier 4 may be found just to the right of the ruddy star Antares in Scorpius, while my favorite globular, Messier 22, lies just to the left of the star Kaus Borealis, which marks the ôtopö of the ôTeapotö asterism in Sagittarius. There are at least a dozen more of these objects awaiting your view in this part of the sky.
Closer to home the planet Venus hangs above the western horizon during evening twilight. You should have no trouble finding her about half an hour after sunset, but she disappears just after 10:00 pm.
Saturn remains the only easily observable planet for evening skywatchers. The ringed planet is now just west of the meridian as twilight fades, so you only have a few hours to enjoy the view of him through a telescope. Saturn reaches the second stationary point of this yearÆs apparition on the 9th, pausing his westward creep against the stars and resuming his slow plod eastward. This is a good time to observe him with the telescope since the planetÆs sphere now casts a noticeable shadow on the eastern portion of his distinctive rings. When you tire of looking at fuzzy globular clusters, round out your evening enjoying the always amazing view of this distant planet!