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Astronomy Chapters 22-24 Early Astronomy • Astronomy is the study of the universe. • Golden Age of astronomy centered in Greece (600B.C. –A.D. 150). • Aristotle concluded that earth was round because saw round shadow of earth on moon. Early Astronomy • Greeks believed in geocentric model of the universe. • “Geo” means Earth • Geocentric model- the Earth was a sphere that stayed motionless. The moon, sun, and known planets- Mercury, Venus, Mars, Jupiter- orbit the Earth. Early Astronomy • Later Aristarchus (312-230B.C.) was first to believe in a sun-centered universe. • “Helio” means sun • Heliocentric model- Earth and other planets orbit the sun. Planetary Movement Facts: The orbit of each planet around the sun is an eclipse or elliptical in shape. A planet’s distance to the sun is expressed in astronomical units or AUs. An AU is the distance of the Earth to the sun, about 150 million km. Earth’s Moon • The Giant Impact Hypothesis accounts for origin of Earth’s moon. • The Giant Impact HypothesisWhen solar system was forming, a body the size of Mars struck Earth. Ejected materials entered Earth’s orbit, forming the Moon. Formation of Solar System • Nebular Theory- sun and planets formed from a rotating disk of dust and gases The Solar System • The planets of our solar system are arranged into 2 groups: Terrestrial Planets and Jovian Planets Terrestrial Planets- Mercury Venus, Earth, Mars Jovian Planets- Jupiter, Saturn , Uranus, Neptune Terrestrial Planets Characteristics: 1. Smaller than Jovian Planets. Example Earth is ¼ size of Neptune. 2. Closer to the sun than Jovian planets. 3. Rockier than Jovian planets. Terrestrial Planets • Mercury- Innermost Planet, smallest • Venus- Veiled Planet-”Earth’s twin”, active lava flows • Mars- the red planet, evidence of water has been found on Mars, easiest to see Jovian Planets- Gas Giants • Jupiter- the Giant planet, 2 1/2 x mass of other planets combined, hydrogen-helium atmosphere, winds cause bands of color • Saturn-the ringed planet, made of ice and rock • Uranus- the sideways planet, rotates on its side • Neptune- the windy planet