The Night Sky of August

Dr. Wayne Wooten
Professor of Astronomy

For August 2012, it is full moon on August 2nd, the Green Corn Moon. The last quarter moon is on August 9th. The waning crescent moon passes by Jupiter on the morning of August 11th, and by Venus on the morning of August 13th. On August 12, it is the peak for the Perseid Meteor Shower, our best annual celestial fireworks show, and the waning crescent moon will sit midway between the two brightest planets.

If you have a dark sky site, you will see about a bright meteor every 5-10 minutes from midnight until dawn. They will seem to come out of the constellation Perseus, rising in the NE just before midnight. The new moon is on August 17th, and the waxing crescent moon passes five degrees south of Saturn on the evening of August 22nd, and then 3 degrees south of Mars later that evening. The first quarter moon is on August 24th, and the second full moon of August, a “blue moon”, is on August 31st. The first two weeks find the moon waning in the morning sky, making the darker evening skies idea for observing the Milky Way.

Mercury will be briefly visible in the morning sky in mid August, just to the lower left of the waning crescent moon on August 15st. It will be directly the very slender crescent moon on August 16th, but soon disappears behind the sun for the rest of August. At the same time, Venus reaches greatest western elongation, 46 degrees west of the Sun on August 15th; through the telescope Venus appears on the edge of its orbit as seen from Earth, and exactly half lit, and 23” of arc across. On August 1st, Venus was a waning crescent, 41% sunlit, and 28” across. By the end of August, Venus is waning gibbous phase, 58% sunlit but now on the far side of its orbit, only 21” across. Mars is moving rapidly eastward in Virgo, passing between Saturn and Spica on August 13-14th. Jupiter rises in Taurus about 3 AM at the start of August, and about midnight by month’s end. It is at opposition on December 3rdt, rising in the east at sunset and up all night. But the best telescopic treat is still Saturn, now moving eastward away from Spica in the southwestern sky. Enjoy the rings, now open about 11 degrees, for by the end of September it will be lost in the sun’s glare in the west.

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. Look for Saturn to the upper right of Spica, and drawing closer to it night by night as Saturn revolves around the sun in its slow 30-year orbit. 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.

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 on the map back page when you download the SkyMap pdf file.

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. It is just below Cygnus and above Aquila that we find the exquisite planetary nebula Messier 27, the Dumb Bell Nebula.

To the south, Antares rises about the same time in 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.

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. This stellar nursery is ablaze with new stars and steamers of gas and dust blown about in their energetic births. In the same binocular field just north of the Lagoon is M-20, the Trifid Nebula.

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