For Northern Hemisphere skywatchers, August is usuallyregarded as "meteor month," with one of the best displays of the yearreaching its peak near mid-month. That display is, of course, the annualPerseid meteor shower beloved by everyone from meteor enthusiasts to summercampers.
This year experts predict an excellentPerseids display, as peak activity will coincide with a new moon, meaningdark skies that allow the meteors to shine.
Meanwhile, there are other lesser-known summer meteordisplays to check out right now.
When to watch
In general, the Earth encounters richer meteoric activityduring the second half of the year. And you're more likely to see twice as manymeteors per hour in the predawn hours as compared to the evening hours. Here'swhy: During the pre-midnight hours we are on the trailing side of the Earth asit moves through space. Any meteoric particle generally must have an orbitalvelocity greater than that of the Earth to "catch" us. Aftermidnight, when we have rotated onto the Earth's leading side, any particle thatlies along the planet's orbital path will enter our atmosphere as a meteor.
In these head-on collisions,meteors hit our atmosphere at speeds of 7 to 45 miles per second. Their energyof motion rapidly dissipates in the form of heat, light, and ionization,creating short-lived streaks of light popularly referred to as "shootingstars."
Summertime meteors are especially noticeable betweenmid-July and the third week of August. And between Aug. 3 and 15, there are sixdifferent minor displays. When they run (and peak):
- Southern Delta Aquarids, July 12-Aug. 19 (July 28), 15 per hour, faint, medium speed.
- Alpha Capricornid, July 3-Aug. 15 (July 30), 4-5 per hour, slow, bright, a few fireballs.
- Southern Iota Aquarids, July 25-Aug. 15 (Aug. 4), 1 to 2 per hour, faint, medium speed.
- Northern Delta Aquarids, July 15-Aug. 25 (Aug. 8), 1 to 4 per hour, faint, medium speed.
- Kappa Cygnids, Aug. 3-Aug. 25 (Aug. 18), 1 to 3 per hour, slow moving, sometimes brilliant.
- Northern Iota Aquarids, Aug. 11-31 (Aug. 20), 1 to 3 per hour, faint, medium speed.
How to watch
The only equipment you'll need is your eyes and a modestamount of patience. Telescopes and binoculars are of no use for fast-movingmeteors.
The actual number of meteors a single observer can see in anhour depends strongly on sky conditions. The rates above are based on a limitedstar magnitude of +6.5 (a really good sky), an experienced observer, and anassumption that the radiant is directly overhead. The radiant is the place inthe sky where the paths of shower members, if extended backward, wouldintersect when plotted on a star chart.
Your clinched fist held at arm's length is equal to roughly10-degrees on the sky. So if the radiant is 30-degrees ("three-fists")above the horizon, the hourly rate is halved; at 15-degrees it is a third.
While the hourly rates from these other meteor streams arebut a fraction of the numbers produced by the Perseids, combined, overall theyprovide a wide variety of meteors of differing colors, speeds and trajectories.
The Southern Delta Aquarids, for example, can produce faint,medium speed meteors. The Alpha Capricornids generate slow, bright, longtrailed yellowish meteors. And the Kappa Cygnids are classified as slow-movingand sometimes producing brilliant flaring fireballs.
Note that five of the six showers listed, come from theregion around the constellations of Aquarius and Capricornus. Theseconstellations are highest in the southern sky between roughly 1 and 3 a.m.local daylight time, so that's generally the best time to watch.
And don't forget to reserve the overnight hours of Aug.12-13 for observingthe Perseids, which under clear, dark skies will produce one or two meteorsevery minute.
- 2007 Perseid Meteor Shower
- Sky Calendar & Moon Phases
- Astrophotography 101
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 otherpublications, and he is also an on-camera meteorologist for News 12 Westchester, New York.