For skywatchers in the Northern Hemisphere, late summer is usually regarded as the prime "meteor-viewing season," with one of the best displays of the year reaching its peak in mid-August. But some lesser-known summer meteor displays can still dazzle.
The summer meteor shower season hits its peak with the annual Perseid meteor shower, which is usually beloved by everyone from meteor enthusiasts to summer campers in August. This year will be an excellent one for the Perseids, as their peak will nearly coincide with a new moon, which should offer dark skies for prospective observers.
But the Perseids aren't the only meteor show in town. [Stunning meteor shower photos.]
Meteor shower basics
In general, the Earth encounters richer meteoric activity during the second half of every year. And skywatchers are more likely to see twice as many meteors per hour in the predawn hours as compared to the evening hours.
This is due to the fact that during the pre-midnight hours we are on the "trailing" side of the Earth, 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 the Earth's "leading" side, any particle that lies along the 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."
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 that are active. These six are listed in the accompanying table. [Table: Summer Meteor Shower Viewing Guide]
The only equipment you'll need is clear weather, your eyes and a modest amount of patience.
What you might see
The actual number of meteors a single observer can see in an hour depends strongly on sky conditions. The rates given in the table are based on a limited star magnitude of +6.5 (considered to be the faintest star visible to the naked eye without the use of binoculars or a telescope; 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 (about three fists in size) above the horizon, the hourly rate is halved. At 15 degrees it is one-third.
While the hourly rates from these other meteor streams provide 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.
Among these are the Southern Delta Aquarids, which can produce faint, medium-speed meteors; the Alpha Capricornids, described as "slow, bright, long-trailed yellowish meteors" and the Kappa Cygnids which are classified as "slow moving and sometimes producing brilliant flaring fireballs." As such, if you stay out and watch long enough, you may be nicely rewarded for your time spent.
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. The Kappa Cygnids appear to emanate from the constellation Cygnus, which will appear more or less overhead within an hour of local midnight.
Moon muscles in
Currently the one drawback in watching for meteors is the moon, which will reach full phase on July 25. Since it will be in the sky practically the entire night, the brilliant light of July's full moon will likely obscure all but the very brightest streaks.
But in the nights that follow, the moon will be rising progressively later in the night as well as waning in phase and brightness. After Aug. 3, the moon will have diminished to a crescent phase and will become significantly less of a hindrance to viewers.
- Gallery ? Perseid Meteor Shower, Part 2
- Beginner Astrophotography Telescopes
- July's Full Moon Rises Sunday With 'Sea Goat'
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 News 12 Westchester, New York.