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Hal Kibbey

Last modified: Wednesday, July 31, 2013

Star Trak: August 2013

July 31, 2013

BLOOMINGTON, Ind. -- The annual Perseid meteor shower, which will peak on the night of Aug. 11-12, is one of the most popular every year because it happens on warm summer nights. In a clear, dark sky there may be as many as 60 bright meteors per hour, some with smoke trails that last several seconds after the meteor has vanished. Start observing around midnight local daylight time. The crescent moon will set before midnight, so it won't interfere.

The Perseids will be visible for most of August, though there will be fewer meteors to see the further from the peak date you watch. If the peak is hidden by clouds, try looking for meteors again as soon as the night sky is clear.

To minimize the effect of local light pollution, which can obscure as many as half of the meteors, try to avoid artificial lights. Face east if you have a clear view in that direction, and look about half way up the sky from the horizon. You won't need binoculars or a telescope because the meteors move much too fast for those. The chances of seeing a fireball will be greatest near dawn, when Earth will be moving head on into the meteor stream.

The Perseids may appear anywhere in the sky, but they will seem to originate from a point called the radiant in the constellation Perseus, which gives the meteors their name. The higher the radiant is above the northeastern horizon, the more meteors will be visible. Perseus is just north of the W-shaped constellation Cassiopeia in the Milky Way, with the bright star Capella and the Pleiades star cluster below it. Meteors near the radiant will have short trails because we see them nearly end on, while those far from the radiant will look longer because they are seen from the side.

Most meteor showers happen when Earth crosses the orbit of a comet; the Perseids come from Comet Swift Tuttle. The meteors are caused by particles released from the comet's nucleus and left behind in space. As Earth plows through this stream of debris, ranging in size from sand grains to pebbles, each particle slams into our atmosphere at a speed of more than 30 miles per second and burns up almost instantly from friction with air molecules. The resulting heat momentarily creates a streak of glowing air that we see as a meteor (sometimes called a "shooting star" or "falling star"). All of this happens about 50 miles above the ground, regardless of how close some meteors may appear.


Venus will shine through the bright glow of evening twilight a half hour after sunset all month, appearing about 15 degrees above the western horizon each evening as seen from mid-northern latitudes. The brilliant planet will remain at about the same altitude all month, setting about an hour and a half after the sun. By month's end it will be 5 degrees to the lower right (west) of the bright white star Spica.

At the beginning of August, Saturn will be about 30 degrees above the southwestern horizon when it comes into view about 45 minutes after sunset to the upper left (south) of Spica. Saturn and Venus will rapidly approach each other as the days pass, and by the end of the month Saturn will set just an hour after Venus and two and a half hours after the sun.

Saturn's rings will be tilted 17 degrees to our line of sight during August. Any telescope will show Saturn's biggest moon, Titan, which will be north of the planet Aug. 2 and 18, and south of it Aug. 10 and 26.

Jupiter will rise around 3:30 a.m. local time as August begins, followed 20 minutes later by Mars. Both will be about 20 degrees above the eastern horizon 45 minutes before sunrise Aug. 1. The two planets will rise earlier each day, and sunrise will happen later. By Aug. 31, Jupiter will rise around 2 a.m. and provide interesting views through a telescope. Mars will be much farther from Jupiter and about 5 degrees west of the Beehive star cluster.

On Aug. 1, Mercury will be 10 degrees above the east-northeastern horizon a half hour before sunrise. Though it will be brighter each morning after that, it will gradually appear lower until it disappears from view around mid-month. It will pass behind the sun Aug. 24.

Light pollution

If you look at the constellation Cassiopeia in the northeast on a clear summer night, and you can't see the Milky Way sprawling high across the sky from the northern to the southern horizon, then your sky has significant light pollution, which is the case for about two-thirds of the world's population. This dimming of the night sky is caused by excessive artificial lighting, much of which is wasted.

Moon phases

The moon will be new on Aug. 6, at first quarter on Aug. 14, full on Aug. 20 and at third quarter on Aug. 28.