YOU may have already missed the Iota Aquarids and the Alpha Capricornids and later in the month it will hardly be worth your trouble waiting up to see the Kappa Cygnids. But over the coming weekend the Perseids may well provide an evening to remember.
These are not, as you might imagine, casual upper class acquaintances from the Aegean who may have arrived in the hope that some long forgotten Grecian act of hospitality will be repaid. They are a different shower entirely - the August meteors among whom, as always, the Perseids seem set to be the most spectacular.
Shooting stars, or meteors, are a kind of space pollution - tiny specks of interplanetary dust that become visible by frictional incandescence as they encounter the rarefied air of Earth's upper atmosphere.
Occasional meteors may be seen on any clear and moonless night, but at certain times of the year their number increases very markedly. This occurs when Earth, in the course of its passage around the sun, encounters a concentration of the meteoric dust, the result being what we call a meteor shower.
The main meteor showers are regular and predictable features of the astronomical calendar. They have quaint, unusual names, in most cases taken from the constellation from which the meteor shower appears to emanate.
The Quadrantids, for example, appear in early January, the Aquarids in May and the Orionids in mid October. The Perseids occur in August and this year they will peak very early next Monday.
The Perseid meteor shower is related to debris lying in the wake of comet Swift Tuttle, a body which is relatively close to us at present. Comets orbit the sun, just as the planets do, but they move on a very eccentric, elongated path.
Swift Tuttle spends most of its time millions of miles away in outer space and approaches Earth only every 130 years; its time was ripe in this respect three years ago, when it was to be seen, albeit only through binoculars, as a bright unusual object in the western sky.
Just after midnight on Monday next, August 12th, Earth will cross the trail of particles left in the wake of the departing Swift Tuttle, and the associated meteor shower, already active in a small way, will build to a peak around that time, concentrated in the north eastern quad rant of the sky.
The astronomers, with their usual uncanny confidence, predict that the moon will not rise above the horizon until later in the night, so its brilliance will not interfere with the display. Meteorologists, as always, are more circumspect; it remains to be seen if cloud obscures the view.