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.
the study of space beyond Earth's atmosphere.
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.
large ball of gas and plasma that radiates energy through nuclear fusion, such as the sun.
scientific instrument that uses mirrors to view distant objects.
all known matter, energy, and space.