16 questions · Astronomy & Space
In the spring of 1066 a bright star with a long tail hung over Europe. In England it was taken as an evil omen, and a few months later King Harold fell at Hastings. On the Bayeux Tapestry men point at the sky, the tailed star above them. Only in 1705 did Edmond Halley realise that this visitor returns regularly, roughly every 76 years. Halley’s Comet last appeared in 1986 and will be back in 2061. A comet is essentially a dirty snowball, a nucleus of ice and dust often only a few kilometres across. As it approaches the Sun the ice evaporates and forms a glowing envelope, the coma, and the solar wind blows the tails out of it. Jan Oort guessed where these wanderers come from: the long-period ones from a distant cloud of ice far out, the Oort cloud, the short-period ones mostly from the Kuiper belt beyond Neptune. Some circle the Sun in a few years, like Encke in just over three, while others leave trails of dust that Earth passes through every year: Swift-Tuttle gives us the Perseids, Tempel-Tuttle the Leonids. The twentieth century brought highlights and letdowns. Kohoutek was hailed as the comet of the century in 1973 and stayed faint. Hyakutake and Hale-Bopp, by contrast, blazed splendidly in 1996 and 1997, and in 1994 the world watched the fragments of Shoemaker-Levy 9 slam into Jupiter. Since then probes have visited these icy bodies: in 2005 a projectile struck comet Tempel 1, and in 2014 Philae landed on Churyumov-Gerasimenko. NEOWISE graced the night sky in the pandemic summer of 2020, and in 2017 ʻOumuamua turned up, the first known visitor from another star system.
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Halley
In 1705 Edmond Halley realised that the comets of 1531, 1607 and 1682 were one and the same, and predicted its return for 1758.
💡 Did you know? Halley did not live to see the return; he died in 1742.
Hale-Bopp
Alan Hale and Thomas Bopp found it in July 1995 on the same night, at different places in the United States.
💡 Did you know? It was visible without a telescope for about 18 months, longer than any other known comet.
Shoemaker-Levy 9
Carolyn and Eugene Shoemaker and David Levy discovered it in 1993; Jupiter’s gravity had torn it apart the year before.
💡 Did you know? Some of the dark impact scars in Jupiter’s atmosphere were as large as Earth.
Churyumov-Gerasimenko
The Soviet astronomers Klim Churyumov and Svetlana Gerasimenko discovered it in 1969.
💡 Did you know? When it landed in 2014, the Philae lander bounced twice before coming to rest in shadow.
Tempel 1
The Deep Impact mission aimed to expose material from inside a comet’s nucleus; Wilhelm Tempel had discovered the comet in 1867.
💡 Did you know? The impact took place on 4 July, American Independence Day.
Encke
In 1819 Johann Franz Encke showed that several earlier sightings belonged to this one comet.
💡 Did you know? Its trail of dust is the source of the Taurids, the shooting stars of autumn.
Swift-Tuttle
It takes about 133 years to orbit the Sun and was last near the Sun in 1992.
💡 Did you know? At about 26 kilometres across, its nucleus is the largest object that regularly passes close to Earth.
Tempel-Tuttle
It circles the Sun about every 33 years; shortly after its visits there can be true meteor storms.
💡 Did you know? In 1833 so many shooting stars fell over North America that some people feared the end of the world.
Hyakutake
Yuji Hyakutake found it in January 1996 with large binoculars; in March it passed only about 15 million kilometres from Earth.
💡 Did you know? The Ulysses probe happened to fly through its tail, which was more than 500 million kilometres long.
NEOWISE
NASA’s NEOWISE space telescope discovered it in March 2020, hence its name.
💡 Did you know? It will not return for several thousand years.
Kohoutek
The Czech astronomer Luboš Kohoutek discovered it in March 1973 at the Hamburg Observatory in Bergedorf.
💡 Did you know? The crew of the Skylab space station observed and photographed it from orbit.
ʻOumuamua
The Pan-STARRS telescope in Hawaii found it in October 2017; at first it was taken for a comet, but it showed no tail.
💡 Did you know? The Hawaiian name means roughly “a messenger from afar arriving first”.
Coma
The solar wind blows two tails out of it: a straight, bluish ion tail and a curved, yellowish dust tail.
💡 Did you know? The word comet comes from the Greek “komētēs”, the long-haired one.
Oort cloud
The Dutch astronomer Jan Hendrik Oort described it in 1950; it probably extends more than a light year out.
💡 Did you know? No one has ever seen it: its existence is inferred from the orbits of comets.
Kuiper belt
It is named after the astronomer Gerard Kuiper; the first object there apart from Pluto was found in 1992.
💡 Did you know? In 2019 the New Horizons probe visited the Kuiper belt object Arrokoth, which looks like a snowman.
1066
It was seen as an evil omen before the Battle of Hastings; beside it the tapestry reads “ISTI MIRANT STELLA”, they marvel at the star.
💡 Did you know? The tapestry is actually an embroidery and about 70 metres long.
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