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Observing the Solar System Ch 14.1 Standards 8.4.c. Students know how to use astronomical units and light years as measures of distance between the sun, stars, and Earth. 8.4.d. Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own light. Earth at the Center Greek Observations “planet comes from the Greek word “wanderers” In a geocentric system, Earth is at the center of the revolving planets and stars. Earth at the Center Ptolemy’s Model Ptolemy’s geocentric model was incorrect, but the motions he recorded in the sky were accurate. People believed the geocentric model for nearly 1500 years after Ptolemy died. Sun at the Center Some people believed in the heliocentric model. Heliocentric: Earth and other planets revolve around the sun. The Copernican Revolution Copernicus worked out the arrangement of the known planets and how they move around the sun. Many people unwilling to accept the geocentric model. Sun at the Center Galileo’s Evidence Galileo used the newly invented telescope to make discoveries that supported the heliocentric model. He discovered that Venus went through phases like the moon. He would not see this if the Earth was at the center. Motions of the Planets Copernicus thought that the planets traveled in a percent circle Tycho Brahe’s Observation When he made his observations, he didn’t even have a telescope! His student was Johannes Kepler Motions of the Planets Kepler’s First Law Kepler used Tycho Brahe’s data to develop the three laws about the motions of the planets. Kepler evnetually found out that Mars’s orbit was a slightly flattened circle, or an ellipse (oval shape). Kepler’s Second Law Speed of planets change as they go around the sun Faster when closer to the sun, slower when further away Motions of the Planets Kepler’s Third Law Planets that are closer to the sun, like Mercury and Venus, orbit the sun faster than the ones further away, like Neptune and Uranus Modern View of the Solar System Components of the Solar System Planets vary greatly in size and appearance Moon: natural satellite that revolves around a planet Mercury and Venus don’t have moons Solar System consists of the sun, the planets, and their moons, and several kinds of smaller objects that revolve around the sun. Modern View of the Solar System Measuring Distances in the Solar System Astronomical unit: the Earth’s average distance from the sun About 150 million kilometers On average, Saturn is 9.6 times further from the sun than Earth. Modern View of the Solar System Exploring the Solar System We still use telescopes, like Galileo, but we can put telescopes in space to get a closer look Sun is the source of all visible light in the solar system Just like the moon reflects the sunlight, the other planets reflect sunlight. Also have launched many space probes to put on other planets so we can get samples of what their surface is made out of. Names of the Planets! Roman Name Greek Name Their Role Mercury Hermes Messenger God Venus Aphrodite Godess of Love Mars Ares God of War Jupiter Zeus King of Gods Uranus Kronos God of Time Neptune Poseidon God of Seas Pluto Hades God of Underworld & Precious Metals