The annual Perseid meteor shower is cranking up and is expected to peak around 2 a.m. MDT Thursday, Aug. 13. The timing this year is perfect for meteor watchers in western North America, plus, the moon will be in its new phase, leaving the sky nice and dark for meteor watching.

The Perseid meteor shower is the “old faithful” of meteor showers because, under good sky conditions, it dependably produces between 60 and 100 “shooting stars” per hour, at its peak. But don’t wait for the peak — you can expect to see about 15 to 30 meteors per hour before dawn each morning for a week on either side of the peak, as the shower rises to and falls from its maximum activity.

Perseid meteors also are called “St. Lawrence’s Tears” and have been observed every August since at least 258 A.D. That’s when the Romans martyred a Christian deacon named Laurentius on a hot gridiron. As Laurnetius’ family carried away his body, they saw a number of bright streaks shooting across the sky. They believed that the streaks were the fiery tears of Laurentius falling from heaven, and they marveled at the miracle.

Centuries later, sky watchers all over the world continue to marvel at the sight of “St. Lawrence’s Tears” in mid-August every year.

In 1862, American astronomers Lewis Swift and Horace Tuttle co-discovered a comet that now bears their names: Comet Swift-Tuttle. Italian astronomer Giovanni Schiaparelli pointed out that the Perseid meteor particles orbit the sun in the same path as Comet Swift-Tuttle. That was the first indication that comets could be the source of our annual meteor showers.

We now know that the Perseid meteors are produced when the Earth crosses the orbit of Comet Swift-Tuttle in mid-August every year. Tiny bits of dust left in the wake of the comet smash into the Earth’s atmosphere at 130,000 mph and burn up as fiery meteors about 60 miles high.

What we witness as a “shooting star” is not the dust particle itself, but the hot, incandescent column of super-heated air that surrounds it. Particularly large Perseid meteors can leave glowing smoke trails that persist for many seconds or minutes after the meteor’s death plunge.

If you are very lucky, you might even witness what I call a “shadow caster,” a meteor so bright that it casts flickering shadows across the ground.

Perseid meteors can be seen in all parts of the sky, but their trails will all point back toward the constellation of Perseus, rising in our northeastern sky after midnight. You will always see the most meteors between midnight and dawn because that’s when the spinning Earth has you facing the direction from which the meteors are streaming, like looking out of the front windshield of a moving car as snowflakes stream past.

Perseid meteor watching makes a great family activity. Take the kids and find a nice, dark location, roll out the sleeping bags and watch for “St. Lawrence’s Tears.”

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy’s astrophotography website at http://www.jwestlake.com.