Perseid Meteor Shower Trickle Will Soon Become A Torrent

Astronomer Fred Bruenjes recorded a series of many 30 second long exposures spanning about six hours on the night of Aug. 11 and early morning of Aug. 12, 2004 using a wide angle lens. Combining those frames which captured meteor flashes, he produced this dramatic view of the Perseids of summer. Perseids get their name because they radiate from the direction of the constellation Perseus from just below the W of Cassiopeia. Fred Bruenjes

In the past few days several people have mentioned they’ve been seeing more meteors than usual. Late July through mid-August is always one of the best times of years to spot a meteor without even trying. Several different showers overlap from mid-July through mid-August, the reason for the uptick. Three meteor showers are currently active: the Delta Aquarids (July 21 – Aug. 23), Alpha Capricornids (July 11 – Aug. 10) and the Perseids (July 13 – Aug. 26).

The Delta Aquarids peaked a week ago during the full moon with about 15 meteors an hour from a dark, southern-latitude location. Observers in more northerly locales see half that number. The shower radiant or point in the sky from which the shower members appear to originate lies near the star Skat, a.k.a. Delta (δ) Aquarii, located about three fists to the east or left of the planet Mars. The Alpha Caps produce no more than about 5 meteors an hour from near Alpha (α) Capricorni, which is located a little more than a fist above Mars. The shower would hardly be worth noting if it wasn’t for its habit of producing more fireballs than some.

This sky map shows the layout of the constellations better. While Perseids are visible earlier in the evening (from about 10 p.m. on), they’re best after midnight. Stellarium with additions by the author

The Perseids are far better known and offer a greater abundance of meteors with around 50 meteors visible per hour from a moonless, dark-sky site on the peak night of activity (Aug. 12-13). Over the next few nights, you might see 5-10 per hour as we ramp up to next Sunday night’s peak (Aug. 12-13).

Meteor streams can be surprisingly broad. Earth crossed into the fringes of the Perseid stream in the third week of July, will pass through the densest part on the 12-13 and exit two weeks later. All three of these showers consist of dust and small rocks — called meteoroids — strewn by a particular comet as it orbits the sun. The Perseids’ parent comet is 109P/Swift-Tuttle, which completes an orbit once every 133 years. It last dropped into the inner solar system and passed relatively near Earth in 1992, reaching magnitude 5 that fall. I remember it as a fine binocular object with lots of interesting details visible through the telescope. Swift-Tuttle’s next visit won’t occur till 2126, but it’ll be a good one with the comet predicted to brighten to 1st magnitude, easily visible to the naked eye provided light pollution doesn’t destroy the night by that time.

This visualization shows the Earth in the debris stream from comet 109P/Swift-Tuttle on the peak night of Aug. 12-13. Click to see the animation. Peter Jenniskens, Ian Webster with additions by the author

The Alpha Caps stem from comet 169P/NEAT and Delta Aquarids may hail (astronomers are still a bit uncertain) from 96P/Machholz. When Earth flies through these dusty streams, the material slams into the atmosphere at speeds in excess of 50,000 mph (133,000 mph for the Perseids). As the meteoroid crashes into atoms and molecules some 70 miles overhead it knocks off their electrons; as the electrons recombine with the atoms, the release light. That’s what makes a meteor trail.

Ham radio operators exploit the ionized “tubes” of air created by a meteor’s passage to communicate across great distances. Wikipedia

Meteors are streaks of glowing or ionized air. Ions are great reflectors of radio waves, the reason ham radio operators use meteors to send and receive signals from distant locations on Earth. For a couple seconds, the glowing wakes of comet debris act like mirrors for radio waves.

We’ll have more about the Perseids in the days ahead, so check back. For now, be on the alert that any night week you could spot one … or a Delta Aquarid or even an Alpha Capricornid. As comets continue to orbit the sun and slowly crumble, earthlings are guaranteed meteor showers for as far into the future as you’d care to imagine.

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