A previously unobserved meteor shower may stream from the northern sky on the morning of 24 May to produce perhaps the year's best display. Observers in N America may enjoy an excellent view but, sadly, its climax is predicted to occur after daybreak for Britain.
Most meteor showers recur annually as the Earth cuts through streams of particles, called meteoroids, that follow the paths of comets about the Sun. Those meteoroids disintegrate in the upper atmosphere to give us a meteor shower and, because of perspective, appear to diverge from a point in the sky we call the shower's radiant.
A typical comet may only unleash a fresh swarm of meteoroids near the time of its perihelion, the closest point to the Sun. In time, though, these swarms spread out along the orbit so we catch a shower whenever the Earth intersects the comet's orbit, and not just when the comet is nearby.
Recent years have seen comet experts become adept at predicting the evolution of the meteoroid swarms as they spread away from the comet under the influence of the Sun's radiation and the gravitational forces of the planets.
Those same experts have now analysed the past motion of a small comet, 209P/LINEAR, that was discovered as recently as 2004 and follows an eccentric path that takes it from just inside the Earth's orbit out to Jupiter's distance in a current orbital period of 5.03 years. They find that when the comet passed Jupiter two years ago, some of its swarms of meteoroids released during the 19th and early 20th centuries were deflected enough to intersect the Earth's path on 24 May.
The analyses indicate that the resulting meteor shower should peak between 07:33 and 08:49 BST on that morning with rates of about 100-400 meteors per hour, though a storm-force display of more than 1,000 per hour cannot be ruled out. Since we have no data on the comet's activity a century ago, the estimate is uncertain and, indeed, there may be nothing to see after all.
Any meteors will be relatively slow, only some 19 km per second, and diverge from a radiant point that lies 11° from Polaris in the dim constellation of Camelopardalis, the Giraffe. This would entitle the shower to be called the Camelopardalids.
The peak timing is ideal for the USA and S Canada, but observers in Britain can only hope that forerunners of the shower may be glimpsed before twilight and dawn intervene. Our chart plots the view northwards at 03:00 BST from central Britain and shows the radiant roughly midway between the Plough in the NW and the "W" of Cassiopeia in the NE.
Comet 209p/LINEAR, itself, is expected to be a dim object between the 10th and 12th magnitude as it sweeps southwards from Ursa Major at present to pass 6° ENE of Regulus in Leo on 27 May and (harmlessly) a mere 8,295,820km from the Earth on 29 May – one of the closest cometary approaches on record and the closest since Comet IRAS-Araki-Alcock in 1983.
guardian.co.uk © Guardian News and Media 2014