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The Sky This Week, 2017 October 10 - 17

Rambling through the Milky Way.
The "Double Cluster", NGCs 869 & 884
imaged 2013 August 15 from Fishers Island, NY
by Geoff Chester with an Antares Sentinel 3-inch f/6 refractor
and Canon EOS Rebel T2i DSLR.

The Moon wanes in the early morning sky this week, passing through the Last Quarter phase on the 12th at 8:25 am Eastern Daylight Time. Luna begins the week among the stars of winter, which are on the meridian at 6:00 am as morning twilight begins to brighten the sky. She moves steadily eastward toward the rising stars of spring, and occults the bright star Regulus in Leo before dawn on the 15th. The star will disappear behind the Moon’s bright limb at 5:38 am EDT and re-appear from her dark limb at 6:41 am. This event should be easy to view in binoculars.

As Luna swings into the morning sky the evenings benefit by her absence. You still have time to enjoy the last of the summertime constellations and the sweeping glow of the Milky Way, which bisects the sky from southwest to northeast at 8:00 pm, the time of the end of evening twilight. You’ll find the Summer Triangle of the bright stars Vega, Deneb, and Altair crossing the zenith at this time, and skywatchers in rural locations can marvel at the structure of our Galaxy passing through this bright asterism. Note the dark rift that begins to split the Milky Way in the middle of the Triangle. Use binoculars to sweep the bright star clouds that trend to the southwest; you’ll pass by several bright knots of amorphous light that betray the locations of star clusters and gaseous nebulae. These are also great targets for small low-magnification telescopes. Moving toward the northeast, the Milky Way runs through the faint constellation of Cepheus, which resembles a child’s drawing of a house, and the more familiar "W"- shaped grouping of Cassiopeia. The area around these star patterns is chock-full of star clusters, many of which resolve nicely in the small telescope. My favorite small-telescope target in this part of the sky is the so-called "Double Cluster", which can be seen as a bright hazy spot in the Milky Way between Cassiopeia and the bright star Mirfak in Perseus. Binoculars will show two fuzzy spots, but my 3-inch refractor with a wide-field eyepiece will show two distinct clusters of stars set in the background of a Milky Way star cloud. Formally known as NGC 869 and NGC 884, these clusters contain some of the most luminous stars in the galaxy, many of which shine with over 100,000 times the brightness of our Sun.

The early evening is also the time to catch a glimpse of Saturn, which may be found low in the southwest as evening twilight darkens the sky. The ringed planet is the brightest object in the southwestern sky at this hour, and you’ll have to act fast to catch a good view of him in the small telescope as he now sets by 10:00 pm.

Venus and Mars continue to dance in the pre-dawn sky. At 6:30 am you’ll easily spot bright Venus about 10 degrees above the eastern horizon, while Mars will probably require binoculars to spot a few degrees above the brighter Venus. Venus will continue to put more distance between herself and the red planet. By the week’s end they will be almost 8 degrees apart. Look for the slender waning crescent Moon as she passes just over a degree north of Mars on the morning of the 17th.


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