Halley's Comet perihelion (1986)
On 9 February 1986 Halley's Comet made its closest approach to the Sun for the first time in 76 years. A fleet of spacecraft went out to meet it, and ESA's Giotto took the first close-up pictures of a comet's nucleus.
▶ Open this scene in the simulator Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
On 9 February 1986 Halley's Comet passed perihelion, the point in its orbit closest to the Sun. It was its first return in 76 years, since 1910. This time the geometry was poor: at perihelion the comet was on the far side of the Sun as seen from Earth. As a result, the naked-eye view was far less impressive than in 1910.
For science, though, this return was special. For the first time, a group of spacecraft went out to meet a comet. The Soviet Vega 1 and Vega 2, Japan's Suisei and Sakigake, and the European Space Agency's Giotto, five probes in all, approached Halley one after another in March 1986. People called them the Halley Armada.
Giotto went closest. On 14 March it passed about 596 km from the nucleus at 68 km per second, dozens of times faster than a bullet. At that speed even tiny dust grains hit hard, and its camera was knocked out around the time of closest approach. The spacecraft itself survived, and it had already sent back pictures of the nucleus.
The pictures showed a peanut-shaped lump about 15 km long and 8 km wide. Its surface was darker than coal and reflected only about 4 percent of the sunlight falling on it. Gas and dust shot out from just a few spots on the sunlit side, while most of the surface was quiet. The orbit view reproduces Halley's 76-year orbit, which stretches from beyond Neptune to inside the orbit of Venus.
When and where to see it
Halley has passed aphelion, the farthest point of its orbit from the Sun, and is now heading back. Aphelion came in December 2023, about 35 AU from the Sun, beyond the orbit of Neptune. The comet is now so far away and so faint that even the largest telescopes have trouble seeing it. Its next closest approach to the Sun will come in July 2061.
Dust left behind by Halley's Comet comes back twice a year as meteors. These are the Eta Aquariids in early May and the Orionids in late October. They happen when Earth passes near Halley's orbit and the dust burns up in our atmosphere. The sky view shows the radiant in the pre-dawn sky at those times, and selecting Halley in the orbit view reproduces its tilted orbit, which runs in the opposite direction to the planets.
See this for yourself — replay the moment in the orbit view
Past returns and history
Halley's Comet has been recorded for a very long time. The oldest certain record is in Chinese history books from 240 BC. Its 1066 return was stitched into the Bayeux Tapestry, a long embroidered picture from medieval Europe. In 1910, when news spread that Earth would pass through the comet's tail, some people panicked, and sellers even offered “comet pills”.
The United States did not join the 1986 Halley Armada, because its own Halley probe was cancelled for budget reasons. Instead a spacecraft built for another purpose, ICE (formerly ISEE-3), flew through the tail of Comet Giacobini–Zinner in September 1985. That made it the first spacecraft to study a comet up close.
For the 2061 return, perihelion is calculated to fall around 28 July. This time the comet will be on the same side of the Sun as Earth, so it is expected to look much brighter than in 1986. Calculations suggest it could reach about magnitude −0.3 at its brightest. That is similar to the brightest stars in the night sky.
Why it matters
Halley's Comet was the first to show that comets can return on a regular schedule. In 1705 the English astronomer Edmond Halley argued that the comets seen in 1531, 1607 and 1682 were the same object, and predicted that it would return around 1758. Halley died before then, but the comet came back as he had said. The event made it widely known that Newton's law of gravity applies to comets too.
The 1986 observations confirmed and extended an idea about comet nuclei. In 1950 the American astronomer Fred Whipple had suggested that a comet's nucleus is a “dirty snowball” of ice mixed with dust. Giotto showed that such a nucleus really exists, that its surface is very dark and that gas escapes from only parts of it. This picture became the starting point for later comet research.
The Halley Armada was also a fine example of international cooperation. The Vega probes, which arrived first, measured the exact position of the nucleus and passed it on to Giotto. That allowed Giotto to aim to within about 40 km of its target. This joint Soviet, Japanese and European approach was called the Pathfinder concept.
FAQ
Why was the 1986 return so hard to see?
At perihelion the comet was on the far side of the Sun from Earth. Even at its closest it was about 0.42 AU away, more than 60 million km.
How close did Giotto get?
About 596 km from the nucleus on 14 March 1986. Dust impacts knocked out its camera, but the spacecraft survived.
What does the nucleus look like?
It is peanut-shaped, about 15 km long and 8 km wide, and reflects only about 4 percent of sunlight, making it darker than coal.
When will it return?
It will pass perihelion in late July 2061. This time it will be on Earth's side of the Sun and should look much brighter than in 1986.
Related
- Halley's Comet returns (2061)
- Comet Hale–Bopp (1997)
- Comet Hyakutake sweeps past Earth
- Halley's Comet — object index
- Neptune — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.