Tom Burns: The Perseid Meteor Shower 2016


Tom Burns - Stargazing



The best meteor shower of the year, the Perseid shower, is coming up in mid-August. I thought I’d fill you in a bit early so that you can have time to prepare. This year, astronomical conditions conspire to make the Perseids not just the best of the year but perhaps the best meteor shower since the Leonids at the turn of the millennium.

The best time to observe the Perseid meteor shower this year is during the early (and I do mean early) morning of Friday, Aug. 12, from just after midnight until the rising sun spoils the view.

Listen up, meteor maniacs. Heed the following advice, and you’ll be mesmerized by “shooting stars.” Ignore it, and all you’ll be is mosquito food.

This week, I’ll fill you in on what’s happening and why it happens. Next week, I’ll provide some practical advice about observing this year’s shower.

Meteors are streaks of light that flash across the sky. They usually last a second or so. They happen because bits of space debris, most of them about the size of grains of sand, burn up in Earth’s atmosphere.

When you sit back to watch a meteor shower, you’re actually seeing the pieces of comet debris heat up as they enter the atmosphere and burn up in a bright burst of light, streaking a vivid path across the sky as they travel at 37 miles per second.

Normally, the process happens about 40 miles up as the grain hits the boundary between a thin layer of atmosphere and a thicker one.

If you are skeptical, you should be. It would be surprising indeed if you saw a grain of sand burn up at 40 or more miles away.

In fact, you are not seeing the actual speck burn up.

Instead, you are seeing the object heat up the atmosphere around it. That process causes the atmospheric gas to glow in a long train that follows the path of the speck of debris.

On any given night, meteor shower or no, you’ll see at least five meteors an hour if you’re observing from dark, rural skies where the glow of streetlights (or the moon) doesn’t wash out the view.

Meteor showers happen when our planet passes through a cloud of dust laid down by a passing comet, which is essentially a dirty hunk of ice. Showers occur at about the same time every year because Earth returns to the spot in its orbit where the cloud of debris hangs out.

The comet in question here is Swift-Tuttle, which is a scant 16 miles wide. If that sounds tiny, consider that it is the largest known object to repeatedly pass by planet Earth.

As it passes close to the sun where we are, the sun’s energy heats up and vaporizes the ice on the surface of the comet. The dust, rock, and dirt embedded in the ice are thus released, leaving a dusty, dirty, rocky trail that Earth passes through quite regularly every year.

Swift-Tuttle last passed nearby Earth during its orbit around the sun in 1992, and the next time will be in 2126. You’d expect the shower to diminish a bit each year until the debris cloud is replenished in 2126, but this year, we may get the best Perseid shower in decades.

You can thank the planet Jupiter for this year’s excellent display. The planet’s gravity causes the debris trail to clump up in some sections. Meteor experts are predicting that this year, Earth will pass through such a clump, and we may get what is known as an “outburst.”

Meteor showers last anywhere from one night to several nights running, depending on the width of the debris trail left by the comet. They tend to vary in intensity over the course of a single night depending the amount of space junk in the part of the cloud that Earth happens to be passing through. Thus, showers are inherently unpredictable, so don’t shoot the astronomer if their predictions are wrong and this year’s show is a dud.

Still, you can maximize the number of streaks you see by following a few simple guidelines, which I will tell you about next week.

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Tom Burns

Stargazing

Tom Burns is director of the Perkins Observatory in Delaware.

Tom Burns is director of the Perkins Observatory in Delaware.

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