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made the first measurement of the size of Earth for which any details are known.
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His work enabled astronomers to make accurate predictions of planetary positions and solar and lunar eclipses, promoting acceptance of his view of the cosmos in the Byzantine and Islamic worlds and throughout Europe for more than 1400 years.
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put forth the theory that the Sun is at rest near the center of the Universe, and that the Earth, spinning on its axis once daily, revolves annually around the Sun. This is called the heliocentric, or Sun-centered, system.
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His study of the “new star” that appeared in 1572 showed that it was farther away than the Moon and was among the fixed stars, which were regarded as perfect and unchanging.
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, Kepler published the first two of his three laws of planetary motion, which held that planets move around the sun in ellipses, not circles and that planets speed up as they approach the sun and slow down as they move away.
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Established the Law of Universal Gravitation. Concurred that the Earth rotates around the Sun. Provided rationale that explained Kepler's three laws. Newton's three laws of motion and law of gravitation provided a solid foundation for understanding planetary motion.
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A key theoretical development for 20th-century astronomy and cosmology was the development of the theory of relativity, from 1905 to 1915, which eventually led to an explanation of the origin of the universe.