This is an image of comet Halley. Comet Halley takes about 76 years to orbit the sun once.
Image courtesy NASA, ESA/Max-Planck-Institute for Solar System Research

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  • On May 19, 1910, Earth had its closest encounter with Halley’s Comet. Most comets, sometimes called “dirty snowballs” or “icy dirtballs”, usually follow an orbit that keeps them far away from the sun. Those comets are invisible from Earth, even with the best telescopes. However, if a comet gets closer to the sun, heat from the sun may begin to evaporate some of its ice, which releases the comet’s dust and rocks. This material is the “tail” of a comet seen from Earth. 
    It takes about 76 years for Halley’s Comet to make one orbit around the sun, and astronomers have been able to predict its return since the 1700s. Centuries earlier, ancient astronomers from China to Babylonia had accurately, consistently reported seeing the comet, but failed to recognize it as a single object or recurring event.
  • Term Part of Speech Definition Encyclopedic Entry
    accurately Adverb

    exactly or perfectly.

    ancient Adjective

    very old.

    astronomer Noun

    person who studies space and the universe beyond Earth's atmosphere.

    comet Noun

    celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris.

    consistent Adjective

    maintaining a steady, reliable quality.

    encounter Verb

    to meet, especially unexpectedly.

    evaporate Verb

    to change from a liquid to a gas or vapor.

    orbit Noun

    path of one object around a more massive object.

    predict Verb

    to know the outcome of a situation in advance.

    recognize Verb

    to identify or acknowledge.

    sun Noun

    star at the center of our solar system.

    tail Noun

    stream of gas or dust debris behind a comet.

    telescope Noun

    scientific instrument that uses mirrors to view distant objects.