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The Sky This Week, 2016 October 4 - 11

Spotlight on the Moon
Crescent Moon (with Earthshine) and Venus at dusk
imaged 2016 October 3 from the U.S. Naval Observatory

The Moon waxes in the evening sky this week, gracing the southern sky as she waxes to First Quarter, which occurs on the 9th at 12:33 am Eastern Daylight Time. The Moon will be northeast of Saturn on the evening of the 5th, then about the same distance northeast of ruddy Mars on the 7th. She will end the week by moving into the star-poor reaches of the autumnal constellations, passing just three degrees north of the third-magnitude star Deneb Algeidi in Capricornus on the evening of the 11th.

The Moon is the easiest object to observe with a telescope and is certainly the most rewarding celestial target for novice and experienced observers alike. Virtually any kind of optical aid will reveal the tortured surface of our only natural satellite. My personal interest in astronomy began at an early age when I first saw the Moon through my father’s binoculars. Since then I’ve enjoyed poring over the Moon’s craters, mountains, and broad lava plains through many different instruments, and each view has been rewarding. This week is a special one for looking at Luna since the evening of the 8th has been designated as International Observe the Moon Night. Weather permitting I’ll have a telescope set up in my yard so my neighbors can enjoy exploring our nearest neighbor in space. If you have a telescope, no matter how big or small, do the same where you live and open someone’s eyes to the view of another world.

Of course, the waxing Moon adds scattered light to the night sky, so your views of the Milky Way will rapidly wash out as Luna’s phase increases. Fortunately we have plenty of bright summertime stars to enjoy during the evening hours. The stars of the Summer Triangle, Vega, Deneb, and Altair, are high overhead as darkness settles in the early evening and can be followed until the wee hours. Rising in the east is another geometric figure that is one of the signature constellations of the fall. Even though it is made up of second-magnitude stars, the "Great Square" of Pegasus is prominent in the later evening hours. The square is considered to be an asterism that makes up about half of the constellation, which is supposed to represent the mythical flying horse that carried Perseus to the rescue of Andromeda. Each of the characters in this famous tale from antiquity is located in the eastern autumnal sky. The easiest of these to find in a bright sky is Cassiopeia, the vain queen and mother of Andromeda. She can be recognized by a "W"-shaped group of five stars in the northeastern sky.

Venus is becoming more prominent in the evening twilight sky. She pops out of the twilight glow just after sunset in the southwest, and as the sky darkens she becomes almost impossible to miss.

Saturn can be found in the southwest about 20 minutes after sunset, still drifting slowly eastward above the brighter stars of Scorpius. As soon as you see him you can point the telescope in his direction and still enjoy a good view of his wide-open rings, but as the sky darkens he settles into the turbulent air above the horizon.

Mars also becomes visible in twilight as he speeds eastward through the stars of Sagittarius. This week he closes in on Nunki, the Archer’s brightest star. Through the telescope he resembles a tiny gibbous Moon, and if you’re lucky enough to catch a stretch of steady air, you should be able to make out his north polar ice cap.

You can still find Mercury just above the eastern horizon shortly before sunrise this week. He should be fairly easy to spot as the week opens, but each successive morning finds him a little closer to the rising Sun. If you have a very open eastern horizon try to catch the fleet planet in a close conjunction with Jupiter, just emerging from the solar glare.

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