Halley's Comet can be seen from Earth approximately every 74-75 years as it orbits the Sun. It is composed of volatile ices like water, carbon monoxide, and carbon dioxide that sublime when the comet nears the Sun. Halley's Comet last appeared in 1986 and will return in 2061, and a 1986 spacecraft investigation provided new information about its composition, such as having less volatile ices than earlier models predicted.

6. How often can the comet be seen from Earth?
The comet can be seen from earth every 74-75 years.
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What materials make up a comet?
Like all comets, as Halley nears the Sun, its volatile compounds
(those with low boiling points, such as water, carbon monoxide,
dioxide, and other ices) begin to sublime from the surface of its
nucleus.
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What are some facts about the specific comet you are
researching?
 It last appeared in the inner solar system in 1986 and will return
again sometime in 2061 (start charging your camera battery).
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Halley’s Comet appearance in 1986 allowed researchers to
investigate its make up more closely using spacecraft. While
some previous theories were proven correct, other models were
altered with the new information. For example, while earlier
models predicted the comet to feature many volatile ices, the
actual amount was less than first expected.