Catch the big meteor show while you can

By Joe Rao

Skywatching columnist

updated 3:10 p.m. ET Aug. 11, 2008

Every August, just when many people go vacationing in the country where skies are dark, the best-known meteor shower makes its appearance.

It is also the month of "The Tears of St. Lawrence," more commonly known as the Perseid meteor shower.

Laurentius, a Christian deacon, is said to have been martyred by the Romans in the year 258 on an iron outdoor stove. It was in the midst of this torture that Laurentius cried out: "I am already roasted on one side and, if thou wouldst have me well cooked, it is time to turn me on the other."

The saint's death was commemorated on his feast day, Aug. 10. King Philip II of Spain built his monastery place, the "Escorial," on the plan of the holy gridiron. And the abundance of shooting stars seen annually between Aug. 8 and 14 have come to be known as St. Lawrence's "fiery tears."

Viewing prospects
In 2008, the Perseids are expected to reach their maximum on Tuesday.

The time of maximum should be about 1100 GMT (7 a.m. ET) on Aug. 12, Margaret Campbell-Brown and Peter Brown report in the 2008 Observer's Handbook of the Royal Astronomical Society of Canada. If so, the timing is very good for meteor watchers observing before dawn in North America, especially in the western states. And that morning, the waxing gibbous moon sets around 1:30 a.m. local daylight saving time, leaving a dark sky for the following three hours.

Take full advantage of that moonless period. Next year, a last-quarter moon will illuminate the after-midnight sky with its light and will hinder observation of the Perseids.

Comet bits
We know today that these meteors are actually the dross of Comet Swift-Tuttle. Discovered back in 1862, this comet takes approximately 130 years to circle the sun. And in much the same way that the Tempel-Tuttle comet leaves a trail of debris along its orbit to produce the Leonid meteors of November, Comet Swift-Tuttle produces a similar debris trail along its orbit to cause the Perseids.

Every year during mid-August, when Earth passes close to the orbit of Swift-Tuttle, the material left behind by the comet from its previous visits rams into our atmosphere at approximately 37 miles (60 kilometers) per second and creates bright streaks of light in our midsummer skies.

Comet Swift-Tuttle made its most recent appearance sixteen years ago, in December 1992. For several years before and after its 1992 return, the Perseids were a far more prolific shower, appearing to produce brief outbursts of as many as several hundred meteors per hour, many of which were dazzlingly bright and spectacular. The most likely reason was that the Perseids parent comet was itself passing through the inner solar system and that the streams of Perseid meteoroids in the comet's vicinity were larger and more thickly clumped together — hence the reason for the brighter meteors and higher-than-normal meteor rates.

With the comet now far back out in space, Perseid activity has pretty much returned to normal.

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