Observers in ancient Greece noticed that although the stars seemed to move, they stayed in the same position relative to one another. These patterns of stars, called constellations, kept the same shapes from night to night and from year to year. The Greeks thought that Earth was inside a rotating dome called a celestial sphere. Since the word geo is the Greek word for Earth, an Earthcentered explanation is known as a geocentric system. In a geocentric system, Earth is at the center of the revolving planets and stars. About A.D. 140, the Greek astronomer Ptolemy further developed the geocentric model. Like the earlier Greeks, Ptolemy thought Earth was at the center of a system of planets and stars. In Ptolemy’s model, however, the planets moved on small circles that moved on bigger circles. Copernicus was able to work out the arrangement of the known planets and how they move around the sun. A Greek scientist developed the heliocentric system. In a heliocentric system, Earth and the other planets revolve around the sun. In the early 1500s, the Polish astronomer Nicolas Copernicus developed a new model for the motions of the planets. His sun-centered system is also called heliocentric. Helios is Greek for “sun.” Copernicus was about to work out the arrangement of the known planets and how they move around the sun. Later, Galileo used the newly invented telescope to make discoveries that supported the heliocentric model. Copernicus thought that the planets’ orbits were circles. He based his conclusions on observations made by the ancient Greeks. In the late 1500s, Tycho Brahe made more accurate observations of the planets’ orbits. Johannes Kepler analyzed Brahe’s data. Kepler found that the orbit of each planet is an ellipse. An ellipse is an oval shape, which may be elongated or nearly circular. Kepler used the new scientific evidence gathered by Brahe to disprove the long-held belief that the planets moved in perfect circles. Since Galileo’s time, our knowledge of the solar system has increased dramatically. T planets and their moons, and several kinds of smaller objects that revolve around the sun.
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The sun-centered system of planets developed by Copernicus is an example of a(n)Response area model.
Kepler discovered that the orbit of each planet is a(n) Response area, rather than a perfect circle.
An Earth-centered system of planets is known as a(n)Response area model.
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The sun-centered system of planets developed by Copernicus is an example of a(n) heliocentric model.
Kepler discovered that the orbit of each planet is a(n) ellipse, rather than a perfect circle.
An Earth-centered system of planets is known as a(n) geocentric model.
