The Perseid meteor shower peaks next month, but already its forerunners are darting through our night sky. And there are a host of minor showers in summertime that make meteor-watching rewarding on just about any clear night under dark skies.
Anyone gazing at the summer night sky for even a short length of time is likely to spot a few "shooting stars" darting across the sky. In general, Earth encounters richer meteoric activity during the second half of the year.
And you're more likely to see twice as many meteors per hour in the predawn hours as compared to the evening hours. This is becaue we are on the "trailing" side of the earth during the pre-midnight hours, due to our orbital motion through space. So any meteoric particle generally must have an orbital velocity greater than that of the earth to "catch" us.
However, after midnight, when we are turned onto Earth's "leading" side, any particle that lies along Earth's orbital path will enter our atmosphere as a meteor. As such objects collide with our atmosphere at speeds of 7 to 45 miles per second, their energy of motion rapidly dissipates in the form of heat, light and ionization, creating short-lived streaks of light popularly referred to as shooting stars.
Peak activity
The best meteor display of the summer comes during the second week of August.
The annual Perseid shower, at its peak around the nights of Aug. 11 and 12, is capable of producing 50 to 100 fast, bright meteors per hour for a single observer under clear, dark skies. Any city or suburban lighting can reduce these numbers dramatically.
The year 2005 will be a very good year to watch for the Perseids, chiefly because bright moonlight will not interfere; the nearly first-quarter moon will set before midnight, leaving the rest of the night dark for prospective meteor watchers.
The only equipment you'll need is your eyes and a modest amount of patience.
The very first forerunners of the Perseid shower began to appear around July 17. Try watching for them after the waxing moon has left the sky, leaving the predawn hours dark. You'll only see a few per hour at best, but the numbers will begin to ramp up during the second week of August. The last Perseid stragglers may still be noted as late as Aug. 24.
And more ...
To go along with the Perseids, there are at least ten other minor meteor displays that are active at various times during July and August.
While the hourly rates from these other meteor streams are but a fraction of the numbers produced by the Perseids, overall they provide a wide variety of meteors of differing colors, speeds and trajectories.
Among these are the Southern Delta Aquarids, which can produce faint, medium-speed meteors; the Alpha Capricornids, described as slow, bright, long-trailed meteors; and the Kappa Cygnids, which are classified as "slow-moving and sometimes brilliant."
Summertime meteors occasionally flitting across your line of sight are especially noticeable between mid-July and the third week of August. And between Aug. 3 and 15, there are no fewer than six different minor displays.
As meager as the individual hourly rates are with these minor displays, collectively they become strikingly augmented with the annual August Perseids.
British observational meteor astronomer Alastair McBeath comments that August is Perseid month, with "rising sporadic meteor rates, mild weather overnight, several other minor showers on show, and it's vacation time. With no real moonlight interference for the Perseids, all we need are clear skies!"
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for , New York