Halley's Comet perihelion (1986)

Halley's 76-year return, met by the Giotto probe — humanity's first look at a comet's nucleus.

The moment of Halley's Comet perihelion (1986): https://nowsky.org/e/halley-1986 — opens at the right place and time, replayable, no login.

Available views: Orbit ✓ · Sky — (not visible in the sky)

The story

On 9 February 1986 Halley's Comet reached perihelion for the first time in 76 years. The geometry was poor — the comet was on the far side of the Sun at perihelion — so the naked-eye show fell far short of 1910, but for science it was a return without precedent: for the first time a fleet of spacecraft went out to meet a comet.

The "Halley Armada" — the Soviet Vega 1 and 2, Japan's Suisei and Sakigake, and ESA's Giotto — made their approaches in March. On 14 March Giotto passed 596 km from the nucleus and photographed a dark, peanut-shaped body 15 by 8 km, surviving dust impacts at 68 km/s that knocked out its camera.

Whipple's 1950 "dirty snowball" hypothesis was confirmed by eye. The surface was blacker than coal (albedo 4 percent), and gas and dust jetted from only a few spots on the sunward side — most of the nucleus was inactive, which was new.

The southern hemisphere saw a long tail in the pre-dawn sky in March and April; northern cities needed binoculars. The next return is July 2061, with far better viewing geometry. The orbit replay shows the 76-year plunge from beyond Neptune to inside the orbit of Venus.

Why it matters

Halley is the object that created the very idea of a periodic comet. In 1705 Edmond Halley predicted that the comets of 1531, 1607 and 1682 were one body, and its return in 1758 was the first popular proof of Newtonian mechanics. The 1986 return was the first close look at that comet.

The nucleus size, albedo and jet structure Giotto measured became the reference values for every comet model since. Stardust's sample capture in 2004 and Rosetta's landing in 2014 were built on the picture of a dark, inhomogeneous nucleus first seen at Halley.

Five nations' probes sharing orbit data to guide Giotto — the "pathfinder concept" — was an early success of international space cooperation. Because the Vegas fixed the nucleus position first, Giotto's targeting error shrank to 40 km.

How to watch

Halley is now near aphelion beyond Neptune (about 35 AU), a 28th-magnitude speck barely reachable by the largest telescopes. It passed aphelion in December 2023 and is on its way back toward the Sun.

Select Halley in the orbit view for its current position and 76-year orbit, and use the event replay to preview the 1986 perihelion and the 2061 return. The retrograde, 18°-inclined orbit is obvious at a glance.

Halley's dust returns twice a year as meteor showers — the Eta Aquariids in early May and the Orionids in late October. The sky view shows the radiant in the pre-dawn sky at those times.

See this for yourself — replay the moment in the orbit view

Background

The oldest recorded sighting is in Chinese annals of 240 BC, and the 1066 return is stitched into the Bayeux Tapestry. In 1910, when Earth was to pass through the tail, "comet pills" went on sale.

The United States did not join the 1986 armada: its dedicated probe was cancelled for budget reasons, and ICE (the former ISEE-3) took the record for the first comet encounter by crossing the tail of Giacobini–Zinner in 1985.

The 2061 return is computed with perihelion on 28 July and closest approach to Earth on 29 July, peaking near magnitude −0.3 — far brighter than 1986 and well placed for the northern hemisphere.

The 1986 return was observed from space as well. The Soviet Vega 1 and 2, after dropping landers at Venus, went on to Halley and passed 8,900 km and 8,000 km from the nucleus on 6 and 9 March, measuring dust and gas directly; their data fixed Giotto’s aim point. Japan’s Sakigake and Suisei measured the hydrogen corona and solar-wind interaction from 7 million km and 150,000 km. Five spacecraft observing one comet within a few days of each other is an arrangement that has never been repeated.

FAQ

Why was 1986 such a poor showing?

The comet was on the far side of the Sun at perihelion, and even at closest approach it was 0.42 AU away.

How close did Giotto get?

596 km from the nucleus on 14 March 1986; dust impacts destroyed its camera but the probe survived.

What does the nucleus look like?

A dark peanut 15 by 8 km with an albedo of 4 percent — blacker than coal.

When does it return?

Perihelion on 28 July 2061, expected to peak near magnitude −0.3 — much brighter than 1986.

→ More sky news

Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.