Comet Hyakutake

Comet Hyakutake is a long-period comet that passed close to Earth in March 1996, producing a conspicuous naked-eye display and an exceptionally long tail.

Comet Hyakutake's 1996 apparition: Comet Hyakutake's 1996 passage through the inner Solar System, when it became a bright naked-eye object. The apparition made Hyakutake famous and brought its close approach into view.
Comet: A small Solar System body that releases gas and dust when solar heating activates its icy surface. Hyakutake is one instance of this class of active icy bodies.
Yuji Hyakutake: A Japanese amateur astronomer who discovered Comet Hyakutake in January 1996. His discovery brought the comet to attention before its close approach.
Comet observation: The study of comets through visual, photographic, and instrumental measurements. Hyakutake's 1996 passage enabled observations across the electromagnetic spectrum.
Comet Hale–Bopp: A bright long-period comet that was visible to the naked eye in 1996–1997. Its later, prolonged display contrasted with Hyakutake's brief but exceptionally close encounter.
Coma (cometary): The cloud of gas and dust surrounding a comet's nucleus as its surface releases volatile material. Hyakutake's expanding coma reflected sunlight and made the nucleus visible indirectly.
Oort cloud: A hypothesized distant reservoir of icy bodies surrounding the Solar System. Long-period comets such as Hyakutake are thought to originate in this remote population.
Rosetta mission: A European Space Agency mission that orbited comet 67P/Churyumov–Gerasimenko and deployed a lander. Hyakutake's unexpected X-ray emission helped motivate later attention to cometary X-rays.
Comet Hyakutake X-ray emission: X-rays detected from Comet Hyakutake during its 1996 passage near Earth. The observation revealed an unexpected kind of emission from a comet.
Outgassing: The release of gas from a solid when heating causes volatile substances to escape. Solar heating drove gas jets and dust release from Hyakutake's nucleus.

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Hydrogen cyanideBroader topic: Astronomers detected hydrogen cyanide in its coma.