The Perseid meteor shower is one of the most dependable meteor showers. Observers can generally expect 40 to 60 meteors hourly when the shower peaks.
On the evening of August 12th and the morning of the 13th, the Perseid shower should offer its generally reliable display of celestial fireworks. The meteor shower is named, as meteor showers typically are, for the constellation from which the meteors seem to radiate. Several meteor showers appear every year, but the Perseids usually offer the best show.
Meteor Showers are Caused by Comet Debris
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Of course, the meteors are close, becoming visible high in the Earth’s atmosphere less than 100 miles up. Stars are quite distant, being light-years away. By a coincidence of time and space, the Earth’s location in its orbit on August 12th presents the meteors against the backdrop of the constellation Perseus.
The Perseid meteor shower results from debris from the comet Swift-Tuttle, which has an orbit that crosses the Earth’s orbit. Comets are not stable near the sun. Composed largely of ice and small mineral particles, comets tend to melt from the sun’s warmth as they approach. The solid particles are thus left behind marking the path of the comet.
As the Earth passes through the orbit of Swift-Tuttle, particles are pulled toward the Earth by its gravity. In the vacuum of space, the particles can accelerate to many miles per second before entering the Earth’s atmosphere.
When they interact with the atmosphere, frictional forces are created by their great speed as they sweep through the suddenly dense air. The heat of friction causes the small bits and pieces of the comet to be consumed creating a bright streak lasting briefly – generally less than three seconds.
Comet Swift-Tuttle passes just inside the Earth’s orbit once every 133 years and has done so for many centuries leaving debris with each visit. It then retreats to beyond the orbit of Pluto before falling back toward the sun.
Comet Swift-Tuttle may be a Danger to Earth
Although the Perseid meteor shower is a delightful and dependable event, its associated comet is a possible danger to Earth. It is thought to be larger than the object that likely led to the extinction of the dinosaurs, and it passes uncomfortably close to Earth.
The comet was discovered in 1862 and last returned in 1992. Computations of Swift-Tuttle’s orbit indicate that it might come uncomfortably close to Earth and possibly collide with it. That uncertain event is over 2,000 years in the future, so there will be plenty of opportunities to observe the Perseids before things get scary.
Many comets and asteroids are being watched carefully. Collectively called NEOs for Near-Earth Objects, they could cause catastrophic results if they collide with Earth.
Observing the Perseid Meteor Shower
People living in the Earth’s northern hemisphere will have a much better view due to the chance orientation of the Earth’s position as it orbits the sun. Although the peak viewing dates will be on August 12th and 13th, the debris cloud is somewhat diffuse. This means that meteor activity will increase and decrease gradually beginning perhaps two weeks before the peak and tapering off for a similar period afterward.
Best conditions obviously mean a cloudless sky away from light sources of any kind. City-dwellers are at a considerable disadvantage. Find the constellation Perseus on a star chart and begin observing around 11:00 PM facing northeast.
The meteors are bright, competing quite well with the brightest stars. For all their brightness, the debris particles are tiny – generally no larger than sand grains. The high temperatures generated when they burn make them appear to be much larger.
Naked eye observation is best. Binoculars or a telescope offer no real advantage invisibility and can make following the meteors difficult as they appear suddenly and dart quickly across the sky. A reclining lawn chair is a good piece of equipment to have, as it prevents neck strain caused by constantly peering skyward.
Photographing the Meteor Shower
In order to get good pictures of the meteor trails, a camera with a wide-angle lens is best. Most digital cameras allow a wide-angle adjustment. The camera should be mounted on a tripod to ensure steadiness. Aim the camera at the center area where meteors are appearing and open the lens for five or ten minutes if there are no lights to ruin the picture.
Luck will possibly allow the observer to capture a few trails. If the camera does not have a feature that allows the lens to be opened indefinitely, a quick reaction might result in a lucky capture.
The Perseid meteor shower is the most dependable recurring meteor shower. Each year around August 12th the late-night skies produce 40 to 60 or more meteors per hour. The meteors are caused by small solid particles melted off of comet Swift-Tuttle and strewn around its orbit, which the Earth intercepts each August. With a bit of extra effort, the meteor trails can be photographed. A dark sky away from light sources is essential for the best viewing.
Sources:
- “Earthsky’s Meteor Shower Guide,” Earthsky.org
- “How to See the Best Meteor Showers of 2010: Tools, Tips and ‘Save the Dates’,” Jpl.nasa.gov