The Perseid Meteor Shower

In 258 A.D., to distract the masses from constant war under his reign, the Roman emperor Valerian ordered the merciless execution of dozens of leaders of the Catholic church.  Among those martyred was one of the seven deacons of Rome, Laurentius, just 33 years old.  The Roman authorities, rarely subtle, tortured Laurentius by roasting him alive on an iron stove.   Though doomed, Laurentius taunted his captors and 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.”

With that brave comment, Laurentius, now called St. Lawrence, became the patron saint of comedians.  But the date he died, August 10, was also known throughout the world for an annual display of meteors or “shooting stars”.   In medieval Europe, this meteor display became known as the fiery “Tears of St. Lawrence”.  We now call them the Perseids, the finest meteor shower of the year, visible from late July through mid-August.

Like most meteor showers, the Perseids are simply dust-sized pieces of icy debris expelled from a comet, in this case, Comet Swift-Tuttle.  As the Earth passes through the comet’sdebris once each year, some particles streak through our atmosphere and heat up, leaving a transient bright streak we call a meteor.  The tiny particles burn up in the atmosphere.  Very few, if any, make it to the Earth’s surface.  Some hit the moon, too, though they’re too faint to see, even with a telescope.

While the Perseids move into the Earth’s atmosphere on parallel paths, they appear to radiate from a single point in the sky called a radiant.  The effect is similar to falling snowflakes that seem to radiate from a point in front of your windshield as you drive into a snowstorm.  The radiant of the Perseid meteors is found in the northern constellation Perseus. (This excellent image gives you a better idea of how a radiant works.  See how all the meteors trace their way back to a single point?  If you see a meteor whose direction can’t be traced back to the radiant in Perseus, it’s not a Perseid.)


Perseid meteors, traceable back to a point in the sky called the radiant (from Astronomy Picture of the Day)

The Perseids build slowly, starting in late July when you might see 3-4 an hour.  They peak when Earth passes through the thickest part of the debris stream on August 11-12.  At the peak of the show, in clear, dark sky, you might see as many as 60 meteors an hour.

For the best view, observe late on August 11 and the early morning of August 12.  After midnight is best… that’s when the Earth turns into the stream of particles from Swift-Tuttle.

Avoid ambient light if you can.  Lie on a reclining chair or a blanket on the ground, and simply look up.  You don’t need binoculars or a telescope.  You don’t need to look right at Perseus: the meteors can appear anywhere in the sky.  Those with long streaks come into the atmosphere at an oblique angle.  Those with shorter streaks enter the atmosphere at a steep angle and come more directly towards you (no, they will not hit you).

Because the radiant lies in Perseus, northern-hemisphere observers get the best view, though you southerners will see some, too.

It’s the best celestial show of the month.  So hope for clear skies, and get out and see the Perseids if you can.