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Perseid meteor shower illuminates island skies

By Mike Shanahan

Bishop Museum

POSTED:
LAST UPDATED: 09:09 p.m. HST, Aug 05, 2011

Each August brings the return of the year's most famous shower, the Perseid meteor shower. The Perseid shower is well-known because it's a reliable shower, and also because it occurs in mid-summer, when the weather is better.

The Perseids get their name from the constellation of Perseus the Hero, which rises in the northeast right around midnight in mid-August. The shooting stars appear to come from that part of the sky where Perseus is located.

Unfortunately, we'll have a full moon on the peak night, Aug. 13-14. Due to this lunar interference, instead of seeing as many as 100 meteors an hour, we'll more likely see no more than 20 to 30.

Meteor showers are caused when the Earth wanders into leftover comet debris. As a comet approaches the sun in its orbit, the comet leaves a trail of dust behind it. As the Earth orbits the sun, we wander into a given comet's debris at the same time every year. For this reason, shooting-star showers recur at the same time every year. Every August, we wander into the debris left over by comet Swift Tuttle. The little bits of comet dust hit our atmosphere and burn up from the friction, causing the shooting stars of the Perseid meteor shower.

This also explains why meteor viewing is always better after midnight. After midnight, your part of the Earth starts facing into the comet debris. More comet dust hits the atmosphere above your head, and you see more shooting stars.

To see the meteor shower's peak this year, stay up late on the evening of Aug. 13 and into the early hours of Aug. 14. You do not need a telescope or binoculars. Find a location with a good view of the full sky. Get away from any distracting street or house lights. Make sure you are comfortable, since you'll be looking up a lot. You can focus your attention on the eastern sky, but these streaks can appear anywhere.

Viewing should also be good on the night of Aug. 12-13. In fact, the Perseid shower is active from July 23 to Aug. 22.

PLANETS IN AUGUST

At the start of the month, look for Saturn shining about one-third of the way up in the west at dusk (8 p.m.) and setting around 10:30 p.m. Saturn will be only about 10 degrees above the western horizon at dusk and will set by 8:45 p.m.

Saturn shines at 0.9 magnitude. Look for the bright star Spica to the left of Saturn. The two dots of light are almost identical in brightness this month. If you look closely, Saturn has a slightly yellow color, and Spica is slightly bluish.

Look for the crescent moon just below Saturn on Aug. 3. Four weeks later, on Aug. 31, the crescent moon will be just to the left of Saturn, and just below Spica.

Jupiter, the king of the planets, rises in the east at midnight at the start of August and by 10 p.m. at the end of the month. At minus 2.5 magnitude, it cannot be missed. Just look east for the brightest dot. Throughout the month, Jupiter will be high overhead by daybreak. Look for the waning gibbous moon next to Jupiter on the evening of Aug. 19-20.

Mars is still a fairly dim object in the morning sky. It's still 200 million miles from Earth, and shines at 1.4 magnitude, no brighter than an average brightish star. Mars rises in the east around 3 a.m. throughout the month of August. Look for Mars to the left of the famous hourglass shape of Orion the Hunter. While Mars is actually pale orange, it's called "the red planet" in English, and in Hawaiian it's Hoku Ula, or "Red Star." Look for the crescent moon next to Mars on Aug. 25.

Mercury pops into the morning sky at the end of August. Your best chance to spot Mercury this month will be on Aug. 27 around 5:30 a.m. Look for Mercury very low in the east, just below the slender crescent moon. Mercury will still be fairly faint, shining at first magnitude, but the moon can be a handy guide to spotting the elusive planet.

THE AUGUST SKY MAP

The Summer Triangle is high overhead in our August sky. These are three bright stars from three different constellations that form a giant star triangle: the star Altair in Aquila the Eagle, Vega in Lyra the Harp, and Deneb in Cygnus the Swan.

In the southwest, Scorpius the Scorpion is bright and clear. Known here as "Maui's Big Fishhook," it is one of the easiest constellations to find. To the left of Scorpius, look for Sagittarius. The constellation is due south on the map and has a teapot-like shape. The stars of Sagittarius are fairly bright; Capricorn, to its left, is much fainter and looks like a bikini bottom or a big smile.

Farther east, all of Pegasus is now visible. At the heart of the constellation is a square marked by four second-magnitude stars.

Look for the famous Big Dipper very low in the northwest. The pointer stars of the Big Dipper — the two stars in the cup that don't have the handle attached — point to the North Star. Cassiopeia is on exactly the other side of the North Star from the Big Dipper.

Arcturus, the brightest star in Bootes the Herdsman, is in the western sky on this map. You may know it better by its Hawaiian name, Hokule‘a.


Mike Shanahan is director of Education, Exhibits and Planetarium. For more information, go to www.bishopmuseum.org/planetarium/planetarium.html.






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