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The Night Sky of August

Dr. Wayne Wooten
Professor of Astronomy

For August 2010, the Last quarter Moon will be on August 3rd, rising about midnight, and the New Moon will be on August 10th, ideal for observing the Perseid meteor show in the next weekís morning hours. The morning of August 12th is the peak for the Perseid Meteor Shower, our best annual celestial fireworks show.

The Moon will be a thin crescent, setting in early evening, so it will not be a factor when the radiant rises in the NE after midnight. If you have a dark sky site, you will see about a meteor every 2-3 minutes from midnight until dawn. They will seems to come out of the constellation Perseus, hence the name. The waxing crescent moon passes 2 degrees south of Mercury low in the SE on August 12, then below the striking triangle of bright Venus and fainter reddish Mars and Saturn on August 13th. The first two weeks find the moon a crescent in the morning sky and evening skies, making the darker skies idea for observing the Milky Way. The first quarter moon is on August 16th, and the Full Moon, the Green Corn Moon in Native American Lore, is on August 24th.

Mercury will be visible in the evening sky in early August, reaching a greatest elongation of 27 degrees east of the sun on August 7th, but it retrogrades in the next week and will be lost in sunís glare by midmonth. Venus dominates the western sky for the rest of the year, and moves below Saturn on August 8th, then passes below Mars on August 19th. Mars too lies in the evening sky, very distant from earth and not the bright object you may head described in the recycled e-mails revived every August since its close approach to earth in 2003. These are urban legends that will not die, alas. Both Mars and Saturn are setting earlier each evening, and will be lost in the sunís glare by September. But in the east, Jupiter rises in Pisces about 10 PM at the start of August, and about 8:30 PM by monthís end. It is at opposition on September 21st, rising in the east at sunset and up all night.

Those who are used to seeing Jupiter will be surprised by the lack of its southern "racing strike", the usually very prominent south equatorial belt, which vanished this spring and has not grown back to date.

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 Dipperís 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, then 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. Several other good globular clusters are also shown and listed on the best binoc objects on the map back page.

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"Öa 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. About midway between sits the planetary nebula M-27, visible in binoculars. This fine stellar tombstone is our astrophoto highlight of the month. The "dumbbell" nebula was photographed by with a 18" scope and a MalinCam video camera, and is one of the most colorful and photogenic deep sky objects to observe with small scopes. It can in fact be seen with good binoculars.

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 Saturnís orbit!

East of the Scorpionís 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 teapotís 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.

Just a little NE of Sagittarius, and much brighter, giant Jupiter dominates the SE sky in Capricornus. Any small scope will reveal what Galileo marveled at in 1609; four large moons, all bigger or similar to ours in size, orbit it in a line along Jupiterís equator. So get out the old scope, and focus on Jupiter for a constantly changing dance of the moons around the giant world. .

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