2016, August 12: Perseid Meteor Shower


Milky Way and Exploding Meteor
Image Credit & Copyright: André van der Hoeven

The 2016 Perseid meteor shower peaks on the morning of August 12.  The image above shows an animation of a Perseid from the 2015 shower.

Meteor showers occur when the left-over dust particles from a comet, a mashup of dust and ices, intersect our planet’s orbit.  As a comet passes near the sun, the ices vaporize and a trail of dust particles is left behind in the comet’s orbit.  This debris tracks around the sun in or near the host’s comet orbit.  If this orbit crosses the earth’s orbit, the dust particles enter the atmosphere.  The particles’ rapid speed, nearly 40 miles a second, causes friction with the atmosphere and the dust rapidly vaporizes in a flash of light as it streaks through the atmosphere: a shooting star or falling star or, simply, meteor.

Image Credit

A shower from a comet stream appears to emerge from a single spot in the sky, the radiant.  The meteor can appear anywhere in the sky.  The radiant occurs because of the perspective effect like the railroad tracks in the image above where the rails seem to emerge from the train tunnel.

The Perseids are named because their radiant is in the constellation Perseus.

The chart above shows the radiant in Perseus along with the stars Capella and Aldebaran, and the star cluster the Pleiades.  Besides seeing meteors from the shower, other meteors not associated with the shower can be visible.  These sporadic meteors occur nearly randomly.  While Perseids can be seen anywhere in the sky, their pathway can be traced back to the radiant.  Sporadic meteors’ paths do not trace back to the shower’s radiant.

This year, some media outlets are reporting that 150 meteors per hour may be visible on the peak morning.  The Observer’s Handbook is predicting 90 per hour.  These numbers are rates for the entire sky in a very dark location. No single observer can see all these meteor in an hour.  A reasonable estimate for a single observer in a dark location is 15-25 meteors per hour. For a single observer near a city, the reasonable count is 5-15.  In a city, 1-5 meters per hour.

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