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The Night Sky of August

Dr. Wayne Wooten
Professor of Astronomy

For August 2018, the last quarter moon is on August 4th. The new moon is on August 11th, which means there will be little moonlight to interfere with the peak of the Perseid meteor shower on the mornings of August 12-13th this year. From a dark observing site, you can expect about a meteor a minute from 11 PM until dawn, with the radiant, Perseus, rising in the NE about 11 PM. The waxing crescent moon passes six degrees north of Venus in the west on August 14th, and five degrees north of Jupiter on August 17th. The first quarter moon is August 18th. The waxing gibbous moon passes two degrees north of Saturn on August 21st, and seven degrees north of fading Mars on August 23rd. The Full Moon, the Green Corn moon, occurs on August 26th.

While the naked eye, dark adapted by several minutes away from any bright lights, is a wonderful instrument to stare up into deep space, far beyond our own Milky Way, binoculars are better for spotting specific deep sky objects. For a detailed map of northern hemisphere skies, visit the www.skymaps.com website and download the map for August 2018; it will have a more extensive calendar, and list of best objects for the naked eyes, binoculars, and scopes on the back of the map.

Mercury passes between us and the Sun on August 8th, and is lost in the sun’s glare all month. Venus reaches the edge of its orbit at greatest eastern elongation on August 17th. It is 46 degrees from the Sun and appears half lit now from earth-based telescopes. For the next two months, it will be retrograding between Earth and Sun, appearing larger each day, but become a more slender crescent as well, and falling back closer to the Sun each evening. It is at inferior conjunction, passing between us and the Sun, on October 26th, and will be in the morning sky for the rest of the year.

Mars was at opposition in Capricornus on July 27th, and will still be close to earth and bright in the SE all month just after sunset. But the earth has already passed it, so it will be farther away and fainter and smaller in the telescope each evening. In July 2018, our hopes of getting a good look at it were dashed by a huge planet-wide dust storm, so perhaps the dust will settle and let us get better views of it while it is still this close in August. It will not be this close and bright for another 17 years!

Jupiter is still well placed for viewing in the southwest in Libra at sunset. The Great Red Spot is easy to spot with small telescope, as are the four larger moons. Much more distant, fainter Saturn is in Sagittarius, in the south at sunset. Enjoy the rings, now 26 degrees open and tilted toward earth and sun.

The Big Dipper rides high in the NW at sunset, but falls lower each evening. Good scouts know to take its leading pointers north to Polaris, the famed Pole Star. For us, it sits 30 degrees (our latitude) high in the north, while the rotating earth beneath makes all the other celestial bodies spin around it from east to west.

Taking the arc in the Dipper’s handle, we "arc" SE to bright orange Arcturus, the brightest star of Spring. Cooler than our yellow Sun, and much poorer in heavy elements, some believe its strange motion reveals it to be an invading star from another smaller galaxy, now colliding with the Milky Way in Sagittarius in the summer sky. Moving almost perpendicular to the plane of our Milky Way, Arcturus was the first star in the sky where its proper motion across the historic sky was noted, by Edmund Halley.

Spike south to Spica, the hot blue star in Virgo. From Spica curve to Corvus the Crow, a four sided grouping. It is above Corvus, in the arms of Virgo, where our large scopes will show members of the Virgo Supercluster, a swarm of over a thousand galaxies about 50 million light years away from us. One of the largest, M-61, is highlighted this month because this galaxy has a bright starburst core and lies 53 million light years away.

Hercules is overhead, with the nice globular cluster M-13 marked on your sky map and visible in binocs. It is faintly visible with the naked eye under dark sky conditions, and among the best binoc objects in the August sky at night.

The brightest star of the northern hemisphere, Vega dominates the NE sky. Binoculars reveal the small star just to the NE of Vega, epsilon Lyrae, as a nice double. Larger telescopes at 150X reveal each of this pair is another close double, hence its nickname, the "double double"…a fine sight under steady sky conditions.

Below Vega are the two bright stars of the Summer Triangle; Deneb is at the top of the Northern Cross, known as Cygnus the Swan to the Romans. It is one of the most luminous stars in our Galaxy, about 50,000 times brighter than our Sun. To the south is Altair, the brightest star of Aquila the Eagle. If you scan the Milky Way with binocs or a small spotting scope between Altair and Deneb, you will find many nice open star clusters and also a lot of dark nebulae, the dust clouds from which new stars will be born in the future

To the southeast, Antares is bright in the heart of Scorpius. It appears reddish (its Greek name means rival of Ares or Mars to the Latins) because it is half as hot as our yellow Sun; it is bright because it is a bloated red supergiant, big enough to swallow up our solar system all the way out to Saturn’s orbit! Just above the tail of the Scorpion are two fine naked eye star clusters, M-7 (discovered by Ptolemy and included in his catalog about 200 AD) and M-6, making one of the best binocular views in the sky. Your binoculars are ideally suited to reveal many fine open star clusters and nebulae in this region of our Galaxy. Get a dark sky site, and use the objects listed on the back of the August 2018 SkyMap printout to guide you to the best deep sky wonders for binocs.

East of the Scorpion’s tail is the teapot shape of Sagittarius, which marks the heart of our Milky Way galaxy. Looking like a cloud of steam coming out of the teapot’s spout is the fine Lagoon Nebula, M-8, easily visible with the naked eye. In the same binocular field just north of the Lagoon is M-20, the Trifid Nebula. Just east of the pair is the fine globular cluster M-22, faintly visible to the naked eye and spectacularly resolved in scopes of 8" or larger aperture. Look just east of the top star in the teapot of Sagittarius with binoculars.

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