Stargazing in December: A brilliant and unique comet

A astronomical event that will take decades to complete is starting this month, writes Nigel Henbest

Halley’s Comet in 1986 (Getty Images)

This month, an astronomical "event of a lifetime" begins to unfold, at a spot five billion kilometres away in the constellation Hydra. Halley’s Comet, which has been speeding away from us for the past 37 years, is slowed to a standstill by the Sun’s far-reaching gravity on 9 December. It then begins to fall back towards the inner reaches of the solar system, to grace our earthly skies in 2061.

Most brilliant comets – like Hale-Bopp in 1997 – have orbits that last thousands of years or more, and we can’t predict their appearances. Comets in small, predictable orbits have generally been burnt out by multiple encounters with the Sun, and they are now too faint to be visible to the naked eye.

But Halley’s Comet is unique. It’s both bright enough to be a magnificent sky-sight, and follows an orbit small enough to bring it into view regularly and predictably, once every 76 years – closely synced with a human lifespan.