The 2010 Perseids

Background

Perseiid meteor. ©Rick Scott and Joe Orman

The most famous display of its kind, this meteor shower often puts on a spectacular display. This year will be a great year to observe the Perseid meteor shower because the Moon will be nearly New and presents no impediment to . This annual display of bright, fast-moving meteors begins several weeks before the peakand builds to a climax in the early morning hours of August 13 before tapering off quickly. Look for meteors the nights of August 11–12 and 12-13 for the best displays. This year, the waxing crescent moon will not cause much interference with observing the shower as the Moon will set around midnight.

The shower—produced by the earth's passage through debris scattered along the orbit of the periodic comet Swift-Tutte—is impressive to view, but all the more remarkable when one considers that the source of the speeding luminous streaks are tiny grains of dust careening into the upper atmosphere at appproximately 130,000 miles per hour. Friction with the molecules in our atmosphere is violent enough to heat the dust flecks to the point of incandescence and vaporize them (typically at altitudes of 35 to 45 miles above the ground.) From our vantage point on Earth, the meteor trails can be traced back to a point of intersection called the radiant. For this particular shower, that point is located in the constellation Perseus (the hero who rescued Andromeda and slayed the Medusa) and thus gives the shower its name. The radiant is purely an optical illusion since the debris stream is actually a wide path the earth crosses, but this stream appears to vanish at a point in the distance just like the rails of a railroad track appear to converge at the horizon even though the tracks are parallel.

How to Observe the Shower

Meteor showers are one of the great free shows in astronomy. They require no special equipment and can be enjoyed by everyone at the same time. All you need is a dark observing location with an unobstructed view of the sky (the idea is to see as much of the sky as possible, so buildings and trees should be avoided). A comfortable chaise lounge chair or reclining lawn chair provides the most comfort and keep you off the cold, hard ground. Since you'll be spending a lot of time staring up at the sky, a regular lawn chair may lead to a stiff neck very quickly. Hence, the reclining lawn chair or blanket. And remember that it is summer in North America—you may find a light jacket is useful if it gets chilly in the early morning hours (a good rule of thumb is the dress as if it is going to be 20° colder than expected). It is always easier to remove layers if you get too warm than to try and get warm if you have too few insulating layers of clothing. Snacks and something to warm to drink never hurt, either, although be warned that alcohol diminishes night vision. A good bug spray may be a necessity, too, as we are talking about the Dog Days of summer and the mosquito population may be at its most abundant. The bottom line, however, is to make yourself comfortable and enjoy yourself. How you accomplish that is up to you.

Where to Look

Forget about telescopes and binoculars—they only restrict your view of the sky to an area roughly the size of the Full Moon. An unobstructed view of the entire sky is best to enjoy this display. Once the sky has darkened, the shower radiant can be found just above the horizon low in the east. After twilight has ended is a great time to watch for the "earth grazing" meteor that streak along the horizon or disappear below your eastern horizon. Be watchful, however, as meteors can be seen anywhere in the sky and often silently blaze paths that extend over a quarter of the sky. Occasionally a meteor brighter than the planet Venus, or fireball, will slip across the sky leaving a smoky trail to mark its passage. As that fireball disintegrates you may even hear a sizzle or explosion (and exploding meteor is called a bolide).

As the evening progresses, the radiant will climb higher into the eastern sky (due to the eastward rotation of the earth), improving the chances of seeing the meteors after the midnight hours. There are two reasons for the more favorable view after midnight: early in the evening the radiant is near the horizon and roughly half of the meteors will streak towards the east and quickly disappear below the horizon, and after midnight the earth has rotated sufficiently for the night side to now plunge head-on into the meteor stream. For those willing to stay up until 3 a.m. or later, the most favorable view comes in the wee small hours of the morning when the radiant approaches the point directly overhead and meteors fan outward to cover the whole sky.

Additional Links

The Astronomy Picture of the Day
American Meteorical Society
Sky & Telescope's Meteor Page
Science@NASA
SpaceWeather.com

To find out if the weather will cooperate with your observing plans, the latest forecast from the National Weather Service and a nifty up-to-the-minute sky chart can be viewed at The Weather Underground.

Notes on Universal Time

Universal Time (UT) and Greenwich Mean Time (GMT) are used worldwide to avoid confusion between observations in different time zones. To convert from Universal Time to local time, determine the number of time zones between your location and Greenwich, England, then subtract one hour per time zone if you are in the western hemisphere or add one hour per time zone if you are in the eastern hemisphere. For example, the Central Time zone of the Midwestern United States is six time zones west of Greenwich. Therefore, 6 hours must be subtracted from the Universal Time to get Central Standard Time (CST). Or, to convert to Universal Time from Central Standard Time, simply add 6 hours to the current time and adjust the day to the next day if the time turns out to be after midnight (0:00 hours).