One of the great things about August is that it marks the annual return of the Perseid meteor shower. Many people find this the most enjoyable meteor shower of the year. One reason is that it is convenient to spend time outdoors watching it because it happens in the waning days of summer with comfortable nighttime weather, children off from school, and many people on vacation. Another reason is that the Perseids is the most dependable meteor shower of the year. Under clear, dark skies, you may be able to see 80 meteors per hour at peak activity. This year we expect the shower to peak on the night of August 11–12, though many meteors likely will be visible for a few nights before and after that.
What is a meteor? A meteor is a piece of debris (called a meteoroid) that slams into the earth’s atmosphere at high speed and burns up from air friction. This burning causes the flash of light that we call a meteor (or falling star or shooting star). There’s no real danger of being hit, because meteoroids burn up at an altitude of 50 miles or more. In most cases the meteoroids aren’t much bigger than a grain of sand. A meteoroid is a piece of an asteroid or a comet. At a dark site typically you can see four or five meteors per hour almost any night.
What is a meteor shower? As the earth orbits the sun each year, it crosses the orbits of several comets. A comet comes near the sun once each orbit, and as it does it sheds a tremendous amount of material. These potential meteoroids eventually are scattered along the comet’s orbit. When we cross a comet’s orbit, we encounter a much larger than normal number of meteoroids, producing a shower of meteors. This month we cross the orbit of Comet Swift-Tuttle, the parent body of the Perseid meteor shower.
While meteors from a shower may appear anywhere in the sky, if you trace their paths backward, you will find that they appear to come from a particular point. We call this point the radiant, and it marks the direction in space where the meteors are coming from. We name meteor showers after the locations of their radiants. For instance, the Perseid shower radiant lies in the constellation Perseus. There are a number of meteor showers throughout the year, but the Perseids normally is the best.
How can you maximize your enjoyment of the Perseid meteor shower? Here are several tips. First, pick a dark site. Bright lights will reduce the number of meteors that you will see, and cities produce a lot of light, so get as far as possible from any cities, and avoid any local lights. Second, since the meteors can appear anywhere in the sky, pick a location with good exposure in all directions of the sky. Third, more meteors are visible in the early morning hours, so you will have more success if you look for them in the hours before dawn rather than after dusk. Fourth, lie down so that you see the entire sky. Of course, a clear sky is a must. So keep an eye on the weather forecast, and be prepared to adjust the night(s) that you plan to observe the Perseids. Some years a bright moon interferes, but not this year—the moon is a waxing crescent, and it sets relatively early in the evening.