See Several Shooting Star Shows
First of a few astronomy posts.
For Northern Hemisphere skywatchers, August is usually regarded as "meteor month," with one of the best displays of the year reaching its peak near mid-month. That display is, of course, the annual Perseid meteor shower beloved by everyone from meteor enthusiasts to summer campers.
This year experts predict an excellent Perseids display, as peak activity will coincide with a new moon, meaning dark skies that allow the meteors to shine.
Meanwhile, there are other lesser-known summer meteor displays to check out right now.
When to watch
In general, the 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. Here's why: During the pre-midnight hours we are on the trailing side of the Earth as it moves through space. Any meteoric particle generally must have an orbital velocity greater than that of the Earth to "catch" us. After midnight, when we have rotated onto the Earth's leading side, any particle that lies 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 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."
Summertime meteors are especially noticeable between mid-July and the third week of August. And between Aug. 3 and 15, there are six different 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.
The only equipment you'll need is your eyes and a modest amount of patience. Telescopes and binoculars are of no use for fast-moving meteors.
The actual number of meteors a single observer can see in an hour depends strongly on sky conditions. The rates above are based on a limited star magnitude of +6.5 (a really good sky), an experienced observer, and an assumption that the radiant is directly overhead. The radiant is the place in the sky where the paths of shower members, if extended backward, would intersect when plotted on a star chart.
Your clinched fist held at arm's length is equal to roughly 10-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 are but a fraction of the numbers produced by the Perseids, combined, overall they provide 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, long trailed yellowish meteors. And the Kappa Cygnids are classified as slow-moving and sometimes producing brilliant flaring fireballs.
Note that five of the six showers listed, come from the region around the constellations of Aquarius and Capricornus. These constellations 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 observing the Perseids, which under clear, dark skies will produce one or two meteors every minute.
