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Earliest Astronomers Earliest 10,000 years ago – Africa & Europe Symbols carved in bones Counting attempts Moon Phases From 5000 years ago Stonehenge- British countryside, Salisbury Solstice/equinox carvings, drawings, peckings (petroglyphs) Plantings & harvesting Moon phases computer Early Astronomy Ancient Greeks Geocentric Model = Ptolemy Greek Astronomer • In the ancient Greeks’ geocentric model, the moon, sun, and the known planets—Mercury, Venus, Mars, and Jupiter—orbit Earth. Heliocentric Model = Nicolaus Copernicus • In the heliocentric model, Earth and the other planets orbit the sun. Ptolemy Geocentric Theory of Earth thought planets moved in epicycles as they orbited, helped explain retrograde motion was the first to develop circular charts to explain planetary motion Aistotle Copernicus Copernicus concluded that Earth is a planet. He proposed a model of the solar system with the sun at the center. Heliocentric Model This model explained the retrograde motion of planets better than the geocentric model. Early Astronomy Ancient Greeks Ptolemaic System • Ptolemy created a model of the universe that accounted for the movement of the planets. • Retrograde motion is the apparent westward motion of the planets with respect to the stars. March Feb. Jan. Dec. April Sept. May Aug. East June July Retrograde motion of Mars West Retrograde Motion Tycho Brahe (1546-1601) Tycho Brahe designed and built instruments to measure the locations of the heavenly bodies. Brahe’s observations, especially of Mars, were far more precise than any made previously. With the use of his inventions he was the first to accurately record positions of stars and planets Early Astronomy The Birth of Modern Astronomy German astronomer Johannes Kepler (1571-1630) helped establish the era of modern astronomy by deriving three laws of planetary motion. Kepler provided mathematical evidence that explained the positions and motions of planets Johannes Kepler (1571-1630) Kepler discovered three laws of planetary motion: 1. Orbits of the planets are elliptical. 2. Planets revolve around the sun at varying speed. 3. There is a proportional relationship between a planet’s orbital period and its distance to the sun. Early Astronomy Johannes Kepler used Tycho Brahe’s data to develop three laws that explained the motions of the planets. Earth’s orbit June 15th Equal areas (30 days) July 15th January 15th (30 days) Sun December 15th KEPLER’S EQUAL AREA LAW states that a line connecting Earth to the sun will pass over equal areas of space in equal times. Because Earth’s orbit is elliptical, Earth moves faster when it is nearer to the sun. Early Astronomy Equal areas law Faster Slower KEPLER’S EQUAL AREA LAW states that a line connecting Earth to the sun will pass over equal areas of space in equal times. Because Earth’s orbit is elliptical, Earth moves faster when it is nearer to the sun. Early Astronomy Galileo Galilei Italian scientist Galileo Galilei (1564—1642) used a new invention, the telescope, to observe the Sun, Moon, and planets in more detail than ever before. Galileo Called the ―Father of Science‖ Galileo’s most important contributions were his descriptions of the behavior of moving objects Lived Under House arrest because he would not recant his views of a suncentered moving Solar System Early Astronomy The Birth of Modern Astronomy Galileo Galilei • Galileo’s most important contributions were his descriptions of the behavior of moving objects. • He developed his own telescope and made important discoveries: 1. Four satellites, or moons, orbit Jupiter. 2. Planets are circular disks, not just points of light. 3. Venus has phases just like the moon. 4. The moon’s surface is not smooth. 5. The sun has sunspots, or dark regions. Newton English scientist Sir Isaac Newton (1642—1727) explained gravity as the force that holds planets in orbit around the Sun. Early Astronomy The Birth of Modern Astronomy Sir Isaac Newton • Although others had theorized the existence of gravitational force, Newton was the first to formulate and test the law of universal gravitation. The universal law of gravitation, helped explain the motions of planets in the solar system. Universal Gravitation • Gravitational force decreases with distance. • The greater the mass of an object, the greater is its gravitational force. Gravity’s Influence on Orbits Newton’s Laws of Motion 1st Law 2nd Law A body at rest, or in uniform motion, will remain so unless acted upon by an unbalanced force. The change in motion (acceleration) is proportional to the unbalanced force 3rd Law For every action there is an equal and opposite reaction Summary Kepler’s and Galileo’s Laws provided Newton with important clues that helped him formulate his laws of motion Newton arrived at 3 laws that govern the motion of objects The law of inertia The law of force The law of action and reaction Newton also arrived at a law of gravity But it seemed to require action at a distance!