August 12th and 13th are the peak of the Perseids meteor shower; to see them look to the northeast after midnight. The Perseids are one of the more reliable meteor showers of the year, perhaps 60 to 100 are visible each hour when the constellation Perseus is near zenith.
Meteors may be seen radiating outwards from Perseus like spokes on a wagon wheel; the point of origin is known as the radiant. Several factors determine how many meteors are visible during a particular night. Time of night, light pollution, the Moon, height of the radiant above the horizon and the natural variability of the debris giving rise to the meteors themselves.
Meteor showers always best after midnight; from the point of view of the observer, after midnight the Earth plows directly into the meteor stream, before midnight only the faster meteors can catch the Earth. This is why today’s chart is for 2 AM, August 13th. Light pollution and the Moon will wash out the fainter meteors, this will be a particular problem this year as the Moon is very nearly full. Likewise fainter meteors will go unnoticed if the radiant is close to the horizon. The natural variably of the stream is the most frustrating and unpredictable; the dust that makes up the stream comes in random clumps. A thick clump makes a fine meteor shower – the thin ones, not so much.
The dust originates in comet Swift- Tuttle, thrown off of it during its 130 year long trip around the sun. Tonight’s stream was thrown off Swift-Tuttle during it’s 1862 appearance – such a recent stream of dust should be fairly thick and will probably mean a good show. Swift-Tuttle has an orbit that brings it fairly close to the Earth periodically. It’s about 17 miles across, a lot larger than the 6 mile wide object responsible for the extinction of the dinosaurs. If Swift-Tuttle were to hit the earth it would do so with about 27 times the power of the dinosaur impactor. Comet Swift- Tuttle has been called “the single most dangerous object known to humanity”; however there is no chance of collision for at least the next two millennia and only an (almost) insignificant chance thereafter.
The best way to watch this meteor shower is to sit in a reclining lawn chair facing northeast in the darkest place you can find. A few meteors can be glimpsed before midnight, but the majority will only show up in the wee hours of the morning.
See you next time!
Mr. Usher is President of the Everglades Astronomical Society which meets every second Tuesday at 7:00PM at the Norris Center, Cambier Park, Naples.