Sunday, August 8, 2021

Perseid meteors are already beginning to fall in a display that promises to dazzle skywatchers

The Perseid meteor shower will peak on the evening of Aug. 12, just four days after the new moon on Aug. 8, so dark skies should be quite favorable for the annual display, which is one of the most dependable displays of "shooting stars." That's in stark contrast to next August, when the meteors will coincide with a full moon.

Although rates of Perseids will be highest from the early morning hours of Aug. 12 until Aug. 14, all told, the meteor shower will last about two weeks, from July 25 to Aug. 18.

On the evening of Aug. 12, the moon will set at around 10:30 p.m. local daylight time. The display should peak later that night for observers throughout the Northern Hemisphere, especially as morning twilight begins. According to the 2021 Meteor Calendar of the International Meteor Organization (IMO), the Perseids should peak for 12 hours or so, centered on the time when the sun's ecliptic longitude is 140.0° to 140.1° (equinox 2000.0), or  Aug. 12 from 3 to 6 p.m. EDT (1900-2200 GMT).

Observers in Eastern Europe are optimally positioned for the Perseid peak, but North Americans are not far behind. A single observer under dark, clear skies nominally may sight 60 shower members each hour, however, observers with exceptionally dark skies often record even larger numbers.

The Perseids are particularly attractive for introducing the public to astronomy because it is a celestial highlight that can be enjoyed without telescopes or other equipment. In planning a public outreach event, remember that the number of visible meteors can be enhanced substantially by selecting a very dark site that is free of bright lights, haze and smoke.

At the Perseids' maximum, these meteors appear to diverge from a point called the "radiant" located near the famous Double Star Cluster in northern section of the constellation Perseus. As the night progresses, the radiant rises progressively higher into the sky in the northeast until the break of dawn ends observing.

In the United States, the radiant is so far north that it is above the horizon for most of the country when darkness falls. Hence some Perseids can be visible as soon as observing begins, although far fewer meteors appear before midnight, even on the night of the shower's maximum.

Meanwhile, the radiant is always low or below the horizon for places south of the equator such as Australia, New Zealand and South Africa, where few, if any Perseids can be seen.

Meteors appearing close to the radiant — in Perseus and the nearby constellations of Cassiopeia, Andromeda and Auriga — have foreshortened tracks while those far from it will tend to be longer and faster.

Good luck and happy viewing!

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