What's New: August 2020

The Perseids
This year, the Perseid meteors are due to peak on the nights of August 11-12, although activity starts to ramp up around July 17 and will wind down by about August 24. Bright moonlight from the Last Quarter Moon on the 11th will drown out the fainter meteors (though not to the extent that last year’s Full Moon did!).

This shower, like all annual meteor showers, is composed of small particles of interplanetary debris; typically, they are no larger than grains of sand. When these particles enter the Earth's atmosphere at velocities as high as 35 - 40 miles per second (126,000 – 144,000 miles per hour!), they burn up almost instantaneously from friction with air molecules. (The "sensible" part of Earth’s atmosphere is about 100 miles deep, so it is possible that the meteors could make it through in just 2-3 seconds.) Though it may seem as though the meteors are falling over the neighbor’s house or the building up the street, this is an illusion; most of the trails left by these meteors actually occur altitudes of 50 - 75 miles up.

It's also not completely accurate to imply that the particles are approaching and falling upon a stationary Earth. Actually meteoroids (we call them meteoroids when they are still in space, meteors when we see them burning up in the atmosphere, and meteorites on the infrequent occasions they make it to the ground) exist in the form of streams of debris between the planets. These streams are left over from previous passages of comets through the vicinity - in the case of the Perseids, the passage of the Comet 109P/Swift-Tuttle. Every year at this time, the Earth plows through this debris stream like a car encountering a swarm of flies at high speed. Because the post-midnight side of the Earth will be hitting the debris directly and at maximum speed, the best time to view the meteors is generally between midnight and dawn.

Meteor showers are named after their "radiant" – the apparent place in the sky from which they seem to originate if you trace their paths backwards; in this case, the radiant lies in the constellation Perseus. Though the meteors appear to radiate from Perseus, by the time they appear they can be in almost any part of the sky.

Perseid sky chart