Perseid meteor shower: Tips for watching the biggest shower of the year

This week marks the annual return of the Perseid meteor shower, the most reliable meteor shower of the year, though the full moon may interfere with this year's display.

The Perseid meteor shower peaks this week in the overnight hours of Friday and Saturday (Aug. 12 and 13) just before the full moon hits its maximum brightness. If you're preparing to try to catch the light show, here are some meteor basics to get you started:

As the Earth travels in its orbit around the sun, it passes through various streams of interplanetary debris, known as meteoroids. Most of these are left in the wake of comets. Whenever a comet comes near the sun, it gets warmed and sheds material: gas and dust. The gas forms its characteristic tail, and the dust is left behind.

IN PICTURES: Meteors

When the Earth passes through a trail of dust, the dust particles enter the Earth’s atmosphere at high speed, and heat it to incandescence. The rapid bright streaks that result are called meteors. [Amazing Perseid Meteor Shower Photos]

You can go out any night and observe meteors. Most of these are just random particles of interplanetary dust that the Earth happens to encounter, and are known as sporadic meteors.

When the Earth encounters a more concentrated patch of material, we get what is called a meteor shower. A few times in a century, we encounter a major field of meteoroids; the result is called a meteor storm.

It helps to think of these in terms of rainfall. Most of the time, there is no meteor rain, but at certain times, we experience a rain shower: a fine sprinkling of raindrops. On much rarer occasions, we get a full scale rain storm, with large quantities of meteors falling.

The Perseid meteor shower sky map available here shows where to look in the night sky to see this year's meteor shower.

Meteor showers: What to expect

Beginners in astronomy often have false expectations of what a meteor shower is like. They may have read accounts of the once-in-a lifetime meteor storms, where the sky is filled with falling meteors.

The reality is much less spectacular. Think of a meteor shower as the sprinkling of an April shower, rather than an August downpour.

Even though the Perseids are the largest meteor shower of the year, they often disappoint first time viewers. As with many things in astronomy, the key factors to the enjoyment of the Perseids are timing and patience.

Three things define a meteor shower: the time of its peak, the breadth of that peak, and the expected number of meteors per hour.

The Perseid shower is a winner on all three counts. It occurs in the second week of August, when nighttime temperatures are comfortable, it has a much broader peak than average, and it has one of the highest zenithal hourly rates of any meteor shower, 90. This means that if its radiant was directly overhead, the average observer under dark skies would see 90 meteors per hour.

Let’s back up and look at the term "radiant." The radiant of a meteor shower is defined as the apparent point in the sky from which the meteors in a shower appear to radiate.

Perseid meteor skywatching tips

The Perseids get their name because they originally appeared to radiate from a point in the constellation Perseus, though currently the radiant is in Cassiopeia.

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