Halley's Comet

Halley's Comet is the most famous comet in history — the one that made comets predictable. Roughly every 76 years it sweeps in from the outer Solar System, brightens into a naked-eye spectacle, whips around the Sun, and streams back out into the dark. People have recorded its passages for more than two thousand years, from Chinese chronicles of 240 BC to the Bayeux Tapestry.

It owes its name to the English astronomer Edmond Halley, who in 1705 realised that comets seen in 1531, 1607 and 1682 were a single object on a returning orbit, and predicted its comeback for 1758. The comet duly appeared, sixteen years after Halley's death — the first comet ever shown to be periodic, and proof that these apparitions obey the same gravity as the planets.

A dark, icy wanderer

Halley's nucleus is a small, dark, peanut-shaped lump of ice, dust and rock about 15 km long and 8 km wide. Its surface is astonishingly black — an albedo near 0.04, darker than coal — because a crust of sooty organic material coats the ice beneath. Each time it nears the Sun that ice warms and jets away as gas and dust, wrapping the nucleus in a glowing coma and streaming into the long tails that make a great comet.

The 1986 return and the Giotto flyby

Halley's most recent visit, in 1986, was the first to be met by spacecraft. An international armada — the Soviet Vegas, Japan's Sakigake and Suisei, and Europe's Giotto — flew out to intercept it. On 14 March 1986 Giotto passed within about 600 km of the nucleus and returned the first close-up images of a comet's heart, confirming it as a single dark, irregular body venting bright jets on its sunward side.

Two meteor showers

Earth crosses Halley's dusty orbital trail twice a year, and each passage lights up the sky. The debris produces the Eta Aquariids of early May and the Orionids of late October — two reliable annual meteor showers whose "shooting stars" are grains shed by Halley over its many orbits, burning up in our atmosphere.

Where it is now, and when it returns

Halley is currently far out in the cold: on 9 December 2023 it reached aphelion, the most distant and slowest point of its orbit, about 35 AU from the Sun beyond Neptune — and it has now begun the long fall back inward. Its next perihelion is predicted for 28 July 2061, and the geometry will be far kinder than in 1986: the comet will pass on Earth's side of the Sun, coming within about 0.48 AU for what should be a magnificent display.

How to see it

For now Halley is invisible without a large telescope, a faint speck creeping back toward the inner Solar System. But anyone who watches the Orionid or Eta Aquariid meteor showers is already seeing pieces of it. The comet itself returns to naked-eye glory in 2061 — for many readers, a genuine once-in-a-lifetime sight.