Presenting… the Perseids

Though the subject crops up every year around the middle of August, the Perseid meteor shower can sometimes be disappointing because of unfavourable observing conditions, due mostly to the Moon’s presence in the sky. In fact, our satellite is a source of natural light pollution, especially around full Moon, when lunar glare prevents us from seeing all but the brightest Perseid meteors. Fortunately, for astronomers and vacationers alike, this year is promising: the waning Moon will be out of the picture until about 1:00 A.M. on the nights of August 11 to 12 and 12 to 13 — the period surrounding the peak of the shower, which is expected on the morning of the 12th.

Comet dust

The Perseid meteors are actually small particles of debris left in the wake of comet Swift-Tuttle, as it travels, repeatedly, along its orbital path. Each year in August, the Earth moves through this debris stream, and is bombarded by fragments that vary from the size of sand grains to marbles. Upon penetrating the atmosphere, each of these particles vaporises, more or less completely. The released energy causes the air to glow along the particle’s path, and this glowing trail is what we see as a meteor or shooting star. On rare occasions, when larger particles vaporise, their luminous trails can be very bright and persist for several seconds; these are known as fireballs or bolides.

Unlike the observation of most other astronomical phenomena, which requires the use of a telescope or binoculars, the Perseids are best observed with the naked eye. It’s impossible to tell just when or where a meteor will appear, so you’ll need to cast your gaze over the widest area of sky possible. Chose an observing site that’s far from sources of light pollution, with a clear view down to the horizon. Be sure to dress warmly; then just lay back on a lawn chair or a ground pad, and have fun counting meteors! The Perseids will reach their peak on August 12, at 8:00 A.M. (EDT) — that’s well after sunrise in Quebec — so the best time to observe them will be during the nights of the 11th to 12th and 12th to 13th. Though the crescent Moon will rise in the east a few hours before dawn, it will not hinder observations significantly.

The planets

In closing, here’s a word, about the planets this month. Tiny Mercury returns to the morning sky and is easiest to spot during the second and third weeks of August. Look for a thin lunar crescent on the 16th at dawn; it will be about 4 degrees below Mercury, which should help you to locate the elusive planet.

Also in the east at dawn, Venus continues to dominate the sky before sunrise. The waning crescent Moon approaches the brilliant planet on the morning of August 13. Two days before, on the 11th, the Moon is near Jupiter, which is also visible throughout the month in the morning sky.

In the evening, Mars and Saturn remain visible for an hour or so after dusk. Look for them in the southwest near Spica, the brilliant blue star in Virgo: Together, the three objects form a notable triangle. On August 21, the crescent Moon will appear just below the celestial trio.

Clear skies!