Starwatch: A Dazzling Year for the Geminids

The reliable Geminids meteor shower has returned to our sky and, with the Moon as an unobtrusive waning crescent before dawn, we are in for a spectacular display of meteors over the coming week.

Active between the 8th and 17th, the shower is expected to peak overnight on the 13th-14th, bringing more than 100 meteors an hour for an observer under perfect skies. Since high rates persist for more than a day, there should be an excellent show on the previous night, but probably less so on the next one.

The radiant point, from which the meteor paths appear to diverge, lies close to Gemini’s star Castor, which climbs from low in the NE at nightfall to pass high on the meridian at 02:00. Our chart spans some 100° from Leo to Taurus and is centred on Gemini, which stands to the NE of the unmistakable form of Orion. Of course, the meteors appear in every part of the sky – it is just their paths that point back to the radiant.

Travelling at 35km per second, Geminid meteoroids trace long sparkling paths as they disintegrate in the upper atmosphere. However, unlike some meteors, they rarely leave persistent glowing trains in their wake. The meteoroids are thought to derive from the 5km-diameter asteroid Phaethon, which is roasted every 523 days as it sweeps within 21 million kilometres of the Sun at perihelion – closer than any other named asteroid. Its rocks are thought to fracture in the heat, allowing splinters and dust to escape its tiny gravitational pull and spread out around its orbit.

Phaethon passes about 10 million kilometres from the Earth on the 16th in its closest approach since its discovery in 1983, though whether this will result in even more Geminids than usual is questionable. It should be a telescopic object of around the tenth magnitude as it speeds south-westwards from the vicinity of Capella in Auriga on the 11th, through Perseus and Andromeda to the Square of Pegasus.

Also plotted on our chart are Praesepe, the Beehive, in Cancer, and M35, at the feet of Gemini, which are both open star clusters just naked-eye-visible but easy through binoculars. Hydra the Water Snake, the largest constellation, stretches more than 100° around the sky from its head to the S of Cancer to the tip of its tail, which lies S of the conspicuous planet Jupiter in our SE predawn sky. The Moon stands above Jupiter and to the left of Mars on the morning of the 14th.  Star-lovers and sky-enthusiasts can enjoy a meteor shower display on December 13 after 10 p.m., and in the early morning hours of December 14, if clouds and light pollution do not play spoilsport. Reach a spot without city lights, maybe the suburbs, and you can enjoy the Geminid meteor shower. Here, Dr. Debiprosad Duari, Director, M. P. Birla Planetarium, Kolkata explains meteors and the Geminid meteor shower.