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The Sky This Week, 2016 August 9 - 30

The summer vacation edition.
Waiting for darkness, Stellafane Observatory
imaged 2016 August 5 from Breezy Hill, Springfield, Vermont

We’ll be taking our annual summer vacation over the next couple of weeks, hopefully encountering clear dark skies for some pleasant nights of stargazing.

The Moon waxes in the evening sky this week, brightens the overnight hours during the week of the 16th, then wanes in the morning sky thereafter. Full Moon occurs on the 18th at 5:27 am Eastern Daylight Time, with Last Quarter falling on the 24th at 11:41 pm EDT. August’s Full Moon is popularly known as the Corn Moon, Grain Moon, or Sturgeon Moon, indicating the time of year when crops mature for the harvest and fish return to their spawning grounds. Luna forms a very attractive grouping with Mars, Saturn, and the bright star Antares on the evening of the 11th. Over the course of the next few evenings the Moon will pass through the stars of Sagittarius before transiting the star-poor autumnal constellations. She won’t encounter any bright objects until the 25th and 26th, when she drifts past the bright star Aldebaran in the pre-dawn hours.

The highlight of the August sky is the annual Perseid Meteor Shower, which typically peaks in the wee hours on the morning of the 12th. This year you’ll need to stay up well past 1:00 am that morning to see the shower after the Moon has set. Several astronomers who study these phenomena predict that we may be in for an unusually rich display this year since a dense stream material from the parent comet may have been perturbed by Jupiter to pass a little closer to the Earth. This comet, known as 109P/Swift-Tuttle, was co-discovered by astronomers Lewis M. Swift and Horace P. Tuttle in 1862 and orbits the Sun once every 134 years. Each year at this time in August we cross paths with debris shed by the comet as it passes through the inner solar system, and it produces the most consistent of the year’s annual meteor displays. Horace Tuttle went on to have a career at the U.S. Naval Observatory in the latter part of the 19th Century. In addition to the interfering Moon, you should also try to find a viewing location away from city lights. Perseids are noted for their fast speed across the sky and their brightness. About 5 to 10 percent of Perseids produce bright fireballs that leave persistent glowing trains in their wake that can last for several seconds. From a good dark-sky site a single observer may see as many as 100 or more meteors per hour! City dwellers will see much less, but a bright one may be visible from urban yards every few minutes. Observing them is simple; find a place out of the direct glare of street lights, lie down, and look up.

Moonlight wipes out the views of the Milky Way until later in the month, but those views are some of the summer’s best nighttime treats. During the month the sun sets a bit earlier each evening, so by the time the end of the month rolls around the Milky Way should be seen in all its glory by 9:30 pm.

It’s a busy month for the visible planets. During the first week you can still see all five of the naked-eye planets in the evening sky, but by month’s end only three are easily seen.

Venus and Mercury still skulk around the western horizon during early evening twilight. They are spaced by a bit over five degrees for most of the month, with brighter Venus trailing the fading glow of Mercury just a few degrees above the horizon. Binoculars will be a big help in locating them.

Jupiter continues his headlong plunge toward the sunset horizon and can only be seen now in evening twilight. By the end of the month he briefly entertains Venus and undergoes an exceptionally close conjunction with the dazzling planet on the evening of the 27th. This will also occur just a few degrees above the horizon, so binoculars will be helpful to watch the event.

Mars begins the month just south of the second-magnitude star Dschubba, middle star in the "head" of Scorpius, and over the course of the next few weeks overtakes and passes Saturn in his eastward trek along the ecliptic. On the evenings of the 23rd and 24th he passes just under two degrees north of the ruddy star Antares, whose name means "Rival of Mars". These are good nights to compare the colors of the two objects.

Saturn reaches the second stationary point in the current apparition on the 13th, slowly resuming eastward motion along the ecliptic thereafter. He is now the only planet that is easily recognized in the telescope thanks to his distinctive ring system, but by the later evening hours he too is swinging toward the southwestern horizon and the denser layers of air will distort the view.