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The Sky This Week, 2016 September 6 - 13

Sights to see on Moonlit nights.
Epsilon Lyrae, the "Double-double" star in Lyra
imaged 2015 November 16 from Alexandria, Virginia with a 23.5-cm (9.25-inch) telescope

The Moon waxes in the evening sky this week, skirting the southern horizon as she passes through the dense star clouds of the Milky Way. First Quarter occurs on the 9th at 7:49 am Eastern Daylight Time. Luna forms a line with the planet Saturn and the bright star Antares on the evening of the 8th, presenting a very nice photo opportunity. On the following evening you’ll see her just under 10 degrees northeast of ruddy Mars. After passing above the "Teapot" asterism of Sagittarius the Moon begins the long traverse through the sparse starfields of the rising autumnal constellations.

This is the time of the year when we notice the most rapid change in the length of the day. While a similar situation occurs in the spring, I find it more noticeable now since the days are rapidly getting shorter rather than longer. Length of day decreases by about 2.5 minutes per day from now through the end of October, and I have particularly noticed this at sunset. From my point of view this is a good thing since I can set up my telescope and begin enjoying the night sky at a decent hour!

The waxing Moon washes out the fainter objects of the sky including the star clouds of the summer Milky Way, but there are still a number of treats to entertain the telescope owner. High overhead as twilight ends are the three bright stars that form the asterism known as the Summer Triangle. While the star clusters and nebulae fall victim to the scattered light of the Moon, you can find plenty of interesting stars to look at including some of the best of the sky’s double stars. The prime example for this time of year is the star Albireo, which can be seen from suburban skies almost in the center of the Summer Triangle. Your eyes will see this star as a single object, but virtually any telescope with a magnification of 25X or more will reveal two stars with a wonderful color contrast. I like to call Albireo the "Navy Double" due to the contrasting blue and gold colors. This double is ideally suited for small telescopes as larger apertures tend to wash out the apparent colors. For a more challenging target, center the brightest star in the Summer Triangle, Vega, in your finder scope. Two degrees east of Vega you’ll see a pair of stars that form a very wide double that’s easy to see in binoculars. However, if you point a good 3-inch or larger telescope at this wide pair you’ll see that each component is itself a very close double star, thus making the whole system a quadruple group!

The early evening finds bright Venus gradually climbing higher above the western horizon. You may still be able to catch a fleeting glimpse of Jupiter before 8:00 pm, but you’ll need an exceptionally clear night and a flat open horizon. Venus, however, should be quite easy to find as evening twilight deepens.

The Moon pays a visit to Saturn on the evening of the 8th, when she passes just three degrees above the ringed planet. Saturn is also lined up with the bright star Antares in the constellation Scorpius. If you train your telescope on Saturn as soon as you see him in twilight you can enjoy about an hour’s view before he begins to sink toward the horizon haze.

Mars is moving briskly eastward against the background stars, passing between the brighter stars of Scorpius and the "Teapot" asterism of Sagittarius. He has lost much of his luster from opposition in late May, but his distinctive ruddy tint contrasts nicely with most of the stars in the area. You might still try to catch a glimpse of features on his surface, but his disc is now just 10 arcseconds across so you’ll need a good-sized telescope and very steady air.

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