`When shall the stars be blown about the sky?" asks Yeats in his poem The Secret Rose. By all accounts the answer is "Tonight!"
As you will no doubt have read at length in The Irish Times on Saturday, and heard mentioned frequently elsewhere, a spectacular display of shooting stars is likely this evening from 10.30 onwards, as Earth enters the core of Comet Temple-Tuttle's wake.
Even Aristotle and his friends in ancient Greece were well aware that a "shooting star" is not, in fact, a shooting star at all. No matter how many of them "fell" towards Earth, the celestial population of heavenly bodies appeared to stay the same. For want of a better name they called them "things of the air" - or meteors. Meteors are a kind of space pollution, very tiny specks of interplanetary debris. When they encounter the upper part of the Earth's atmosphere they become visible by their own incandescence, produced by the friction of their very rapid passage through the rarefied air. The particles are very small indeed: a shooting star as bright as Venus comes into our atmosphere as a speck of dust which only weighs a gram; some visible meteors are only a tiny fraction of this size.
Meteors may be seen on any clear and moonless night, but at certain times of the year their number increases sufficiently to merit the event being classified a meteor shower. This occurs when Earth, in the course of its passage around the sun, happens to intersect a concentration of the meteoric dust.
Meteor showers are a regular and predictable feature of the astronomer's calendar, and have quaint unusual names, in most case taken from the constellation from which the meteor shower appears to emanate. The Quadrantids, for example, appear in early January, the Aquarids in May; the Perseids have their maximum in early August, and Orionids in mid-October. And the Leonids, occurring around this time, from November 15th to 20th, and appearing, as their name implies, to emanate from the constellation Leo in the eastern sky, promise this year one of the most spectacular meteor showers for quite some time.
Although they occur on the same day every year, the actual intensity of any meteor shower is difficult to anticipate with any accuracy. Indeed, spectacular meteor showers have been comparatively rare in recent years, and were much more common in the 18th and 19th centuries, when they were often mentioned in contemporary writings. But with any luck and cloud-free skies tonight, we may be able to answer Yeats in his own words: "Surely thine hour has come, thy great wind blows".