One of the summer’s most anticipated sky shows is the annual Perseid meteor shower. Owing to the season’s generally pleasant warm nights and the display’s rich offerings, stargazers throughout the Northern Hemisphere set aside at least a few hours to enjoy the bright shooting stars from the constellation Perseus.
Through the ages, comet 109P/Swift-Tuttle has spread motes of dust along its orbit as it passed through the inner solar system. When the Earth sweeps through this band every year, from late July to late August, the dust burns up from friction with the upper atmosphere and creates silent streaks that slice across the sky – the Perseid meteors.
The Perseids are one of the oldest meteor showers that mankind has records for. The earliest observations of this shower were made by the Chinese in 36 A.D. when the Perseids peaked, not in August as they do today, but on July 17. Because the path of the shower is highly inclined to the ecliptic (the plane in which the Earth and all of the other planets orbit the Sun), the Perseids have not been affected by the disturbing gravitational influences of our major planets, and as a result, are a reliable meteor shower. From 714 A.D. until the present year, the Perseids have been recorded every year.
The Perseids, generally seen from about July 20 to August 24, reach a peak hourly rate just before dawn on the mornings of August 12 and 13th. Conditions could not be better for this year’s Perseid meteors: the Moon is nowhere to be seen, and anyone at midnorthern latitudes who can escape city lights might see five or six dozen meteors each hour. Fewer Perseids are expected earlier on these two nights (August 12 and 13th) and for a week before and after.
The tracks of the Perseids, if extended backward, intersect at a point in the sky called the radiant. This is the area from which the meteors appear to emanate and lies between Perseus and Cassiopeia, not far from the Double Cluster. The radiant rises to a decent altitude in the northeast by midnight but climbs still higher in the hours before dawn.
Most Perseids are bright, yellow meteors, with speeds around 36 miles per second and average brightness of +2.3 magnitude. Expect to see several fireballs, which frequently leave trails of smoke and many times explode midway!
Skywatchers who want to make useful meteor counts are encouraged to report to the International Meteor Organization (IMO). The necessary procedures are spelled out on this page, along with where and how to report. The IMO urges observers also to make counts several nights before and after the predicted maximum.
- The Perseids can be seen in August each year, with the maximum activity on August 12 and 13th.
- Comet Swift-Tuttle, the Perseid shower’s parent body, is the largest object known to make repeated passes near Earth – its nucleus is 6 miles across.
- Perseid meteors enter Earth’s atmosphere at roughly 36 miles per second and become visible at around 60 miles up.
- The Perseids, when traced backwards, appear to radiate from the constellation Perseus. This sky map shows the position of the radiant.
