Star Trak: August 2018

BLOOMINGTON, Ind. -- The annual Perseid meteor shower will peak on the night of Aug. 12-13. The Perseid shower is one of the most popular every year because it happens on warm summer nights, when gazing at the starry sky is always enjoyable.

Its peak this year will be less than two days after new moon, so moonlight won't interfere with the display. In a dark sky there may be as many as 150 meteors per hour, with 15 to 30 of the brightest ones visible each hour. Some will leave smoke trails that last several seconds after the meteor has vanished.

The Perseids will be visible for most of August, though there will be fewer meteors to see the farther 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 halfway up the sky from the horizon. You won't need binoculars or a telescope because the meteors move much too fast for those devices. The chances of seeing a fireball will be greatest near dawn, when Earth will be moving head-on into the meteor stream.

The image caption followsView print quality image
An outburst of Perseid meteors lights up the sky in August 2009 in this time-lapse image. Stargazers expect a similar outburst during this year's Perseid meteor shower, which peaks the night of Aug. 12-13. Photo courtesy of NASA/JPL

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 these "shooting stars" 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 straight 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. All of this happens about 60 miles above the ground, regardless of how close some meteors may appear.

Planets

Mars will be bigger and brighter than it has been since 2003 for the entire month of August. Rising just after sunset as the month begins, the Red Planet will be at its highest in the south around 12:30 a.m. in early August but before 10:30 p.m. as the month ends.

Venus will be fairly low in the west after sunset, and its altitude will decrease to 15 degrees during the month. The dazzling white planet will move closer to the bright white star Spica to its left (south) during August until it is only 1 degree below the star on Aug. 31.

Jupiter will appear in the southwest as darkness falls during August, setting in late evening.

Saturn will be highest in the south around 10:30 p.m. as the month begins and two hours earlier by month's end. The planet's famous rings will be tilted almost 27 degrees to our line of sight.

Mercury will be visible before dawn during the last week of August. On Aug. 26 it will be 8 degrees above the eastern horizon 45 minutes before sunrise. Binoculars may be needed to pick the planet out of the predawn glare.

Light pollution

If you look at the constellation Cassiopeia in the northeast on a clear summer night and can't see the Milky Way sprawling high across the sky from the northern to the southern horizon, it means 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. See the International Dark-Sky Association website for more information.

Moon phases

The moon will be at third quarter on Aug. 4, new on Aug. 11, at first quarter on Aug. 18 and full on Aug. 26.

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Hal Kibbey

Phone: 812-336-1333

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Email: hkibbey@indiana.edu

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