It just might be the rainbow in a precipitous weeklong weather forecast.
If the clouds manage to clear early Wednesday morning, astronomy aficionados predict that some of the best meteor showers of the year will be visible. The Perseid meteor shower is set to peak at 1 a.m. on Wedneaday, treating stargazers to somewhere between 20 and 30 meteors per hour, depending on viewing conditions.
"The Perseids are probably the best-watched of any annual meteor shower," according to the National Aeronautics and Space Administration. "They are bright, numerous, and dependable."
The best way to see meteors is to find a dark place with clear sky. Many astronomers prefer mountaintops, but Dartmouth students usually make do with the golf course or the Bema. This year there will be a full moon, which will wash out some of the dimmer meteors with its light.
Standing in a shadow and looking away from the moon will help, Dartmouth astronomy professor Robert Fesen said, noting that the best time to watch is in the hours just before dawn. Most meteors look like little zips of light and last just a fraction of a second.
Thursday and Friday will also be good nights to watch the showers, Fesen said. Although there will be fewer meteors, the moon will not be as bright, so more of them should be visible.
Those who watch in the early evening, however, could be in for a rare treat. Meteors skimming the upper atmosphere, called Earthgrazers, should appear on the eastern horizon. These are uncommon, happening maybe once or twice a night during heavy meteor showers, but they create a brilliant display, lasting several seconds and spanning a large distance. Sometimes they are even different colors.
Around 9 p.m. today is a good time to spot Perseid Earthgrazers because, according to NASA scientist Bill Cooke, "the constellation Perseus will be hanging low near the northeastern horizon -- a good geometry for grazing meteors."
But is watching a meteor shower dangerous? Signs point to no. There have been occasional stories of meteor strikes, however -- in 1982 a five-inch meteor struck a house in Wethersfield, Conn., breaking a hole in the roof, the living room ceiling, then bouncing off the floor, up through the ceiling again into the attic finally making yet another hole in the ceiling on its way down before rolling under the dining room table. Nobody was injured.
Most meteors are much smaller, between the size of a pea and a grain of sand. They ionize the air around them as they zip through the atmosphere, and the light seen in the sky is a trail of these ionized particles. Meteors are comprised of "junk" material floating around in space; in this case, dust and debris left by the comet Swift-Tuttle. As the Earth orbits the sun it occasionally smacks into these clouds of dust and debris, causing a meteor shower.
Fesen likened the visual effects of a meteor shower to driving a car at night in the snow.
"It looks like all of the snowflakes are zooming straight at your windshield, but in reality they are basically standing still," he said.
The darkness just before dawn is a better time of day to see meteors than the darkness just after sunset. The reason for this has to do with the rotation of the Earth. More meteors strike the leading edge of the Earth as it travels through space -- for the same reason that more snowflakes hit the windshield than the back window of the car -- and because of the way the Earth rotates, the hours just before dawn are when you can see that part of the sky.
Indeed, with the annual shower arriving in the skies, a trip outside to observe may be warranted.
According to NASA, "Once you find your observing site and settle in -- a comfortable chair and blankets are recommended -- there's no special direction you have to face. Perseids can appear anywhere in the sky."
