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## ASTRONOMY

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**ASTRONOMY**FAMOUS ASTRONOMERS**Ancient Greeks**• The name "planet" comes from the Greek term πλανήτης (planētēs), meaning "wanderer". • Came up with geocentric (earth center) universe by observing objects moving across the sky.**PTOLEMY-85-165AD**• Believed in geocentric universe (copied the greeks) • earth was the center • used circular orbits with epicycles • was supported by the church for 1500 years**Copernicus-1473-1543AD**• Believed in heliocentric universe • sun was the center • still used the circular orbits**Tycho Brahe 1546-1601AD(just for fun)**• Supreme mathematician who studied the orbits of the planets • had a gold nose • made the best observation of Mars**Kepler 1571-1630**• Studied with Brahe • wrote the Laws of Planetary Motion • gave the planets an elliptical orbit**Galileo 1564-1642**• Perfected and used atelescope • 1. Discovered Saturn’s rings**2. 4 moons of Jupiter**3. Craters on the moon 4. Sunspots on the sun**Newton1642-1727**Wrote the Laws of Motion**Kepler’s Laws of Planetary Motion**P²/ A3= c • 1. Every planets orbit is an ellipse. • 2. An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. • 3. The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies)**Newton1642-1727**Wrote the Laws of Motion • #1 INERTIA • a body at rest /motion • will remain at rest/motion • unless acted upon by an outside force**#2 Newton's law of universal gravitation states that any**two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. • Bigger objects attract smaller ones**# 3 For every action**• there is an equal and opposite reaction**Movements of the Earth**• Rotation: (spin) • Earth spins upon its axis one full time. • 24hrs • Revolution: (orbit) • Earth orbits the Sun one full time • 1 year**Precession**• Earth’s wobble • 1 complete every 26,000 years • Tilt of the Earth 23.5 degrees**Einstein-1879-1955**• Wrote the Theory of Relativity • gravity holds the universe together • Constant motion**Space and light are related**• E=mc2 energy= mass x the speed of light squared**Caption: Einstein's theory of general relativity may be**interpreted in terms of a curvature of space in the presence of a gravitational field.**Speed of light=**• 186,000 mi/ sec • or 300,000 Km /sec**Apparent**Retrograde motion • the motion of a planetary or other body in a direction opposite to that of other bodies within its system as observed from a particular vantage point.