Galileo explains the topography of the moon, as well as the moons of Jupiter, to two cardinals. The Catholic Church ultimately found Galileo "gravely suspect of heresy" for supporting the idea that the Earth revolved around the sun. He remained under house arrest for the rest of his life.

Artwork by Jean-Leon Huens, National Geographic
  • On January 7, 1610, Italian astronomer Galileo Galilei discovered, using a homemade telescope, four moons orbiting the planet Jupiter. Looking at what he thought were a group of stars, he realized the objects appeared to move in a regular pattern. These objects moved in the "wrong direction," according to the understanding of nature at the time. After a few weeks, Galileo determined that he was observing not stars, but objects in orbit around Jupiter. Today, Jupiter’s four largest satellites—Io, Europa, Ganymede, and Callisto—are named the Galilean Moons in honor of their discoverer.

    Galileo’s discovery provided evidence for the Copernican understanding of the universe. This was the idea that everything in existence did not, indeed, move around the Earth. His discoveries would lead to the development of modern astronomy.

  • Term Part of Speech Definition Encyclopedic Entry
    astronomer Noun

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

    astronomy Noun

    the study of space beyond Earth's atmosphere.

    determine Verb

    to decide.

    moon Noun

    natural satellite of a planet.

    Encyclopedic Entry: moon
    orbit Verb

    to move in a circular pattern around a more massive object.

    Encyclopedic Entry: orbit
    planet Noun

    large, spherical celestial body that regularly rotates around a star.

    Encyclopedic Entry: planet
    satellite Noun

    object that orbits around something else. Satellites can be natural, like moons, or made by people.

    star Noun

    large ball of gas and plasma that radiates energy through nuclear fusion, such as the sun.

    telescope Noun

    scientific instrument that uses mirrors to view distant objects.

    universe Noun

    all known matter, energy, and space.