By Stéphane Perron, Whistler Naturalists
A special moment when gazing up at the night sky is to catch a glimpse of a shooting star. Also known as a falling star, the object that flashes across the sky and quickly disappears is properly called a meteor. And every year, on Aug. 12, we can expect to see a substantial number of meteors in the night sky as Earth experiences the annual Perseid Meteor Shower.
Meteors are tiny bits of space debris so small astronomers estimate thousands could fit into the palm of your hand. Yet each of them causes that familiar brief but brilliant flash in the night sky, a dazzling flameout as it ends its existence in a plunge estimated to be around 68,000 kilometres per hour into the upper layers of the atmosphere. On rare occasions, a chunk large enough to survive the fiery plunge hits the ground. It is then known as a meteorite. Each day, Earth collects about 400 tons of meteoric debris, most of it microscopic dust too small to produce a "falling star."
On an average night of the year, three or four moderately bright meteors per hour can be seen, with the rate rising to seven or eight per hour around dawn. However, as Earth navigates its annual orbit around the sun, it crosses the path of comets that are also orbiting our sun. These comets leave a trail of debris behind them as they slowly wear away in their orbit. Every year Earth crosses the same comet debris trails on the same date. We cross about 10 major debris trail every year. It takes one to two days for the Earth to travel through the main part of these comet debris trails and during that time the frequency of meteors intensifies. This is known as a meteor shower.
August 12 is the annual date of peak activity for the Perseid meteor shower. This year, viewing of the Perseids will be hampered by the brightness of the half moon (last quarter) high in the sky. Saturday night, the 11 th to the 12 th , you can expect to see a meteor every four or five minutes in the early evening. However, since the Perseids often produce spectacular early morning-fire balls, it is worth spending a couple of hours outside before dawn, even with the moon in the sky, on the night of peak activity.
The Perseid is one of the most watched meteor showers. It is also one of the most active with 30 to 70 meteors per hour on the peak night, in addition to the half-dozen or so sporadic meteors seen each hour of any night.
Although not as intense, the Kappa Cygnid shower on August 17 th will occur during far better darkness conditions, two days before a new moon.
Meteor watchers use lawn chairs that adjust to a nearly horizontal position so that as much of the night sky as possible is comfortably in view. Select the darkest available site, and face in the direction of the meteor shower, which in the case of the Perseid is the North-East. Remember to have a good supply of blankets. Binoculars or telescopes are useless for observing meteors since Meteors can dart unpredictably from practically anywhere. Since meteor watching requires no specialized equipment, it is a perfect opportunity to introduce others to the night sky or to simply get reacquainted with the mysteries of our cosmos.
Web site of the Week: For more on how best to view the meteor shower, check out: http://spacescience.com/headlines/y2000/ast08aug_1.htm.
August 14 Sunset Nature Walk . Cut Yer Bars trail. Meet in front of the day care at Lorimer Road and Nesters Roads at 7 p.m. Call Mark Jennings (932-5355) for details. Free for members; $2 for non-members.
Sightings and Memberships: NatureSpeak is prepared by the Whistler Naturalists. To become a member or to report noteworthy sightings of mammals, birds, or other species, contact Lee Edwards (905-6448; e-mail: firstname.lastname@example.org).