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1 Chapter 23 Key Terms Solar System Planet Geocentric Theory Heliocentric Theory Orbit Ellipse Dwarf Planet Terrestrial Planet Jovian Planet Asteroid Comet Meteor Meteorite Moon 2 Chapter 23 OUR SOLAR SYSTEM 3 The Solar System Can you name the 8 planets in their order from the sun? Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune New Horizons mission 4 Early Theories Geocentric Theory Before Christ, people believed that the Earth was stationary and everything in our solar system revolved around the Earth Philosophers such as Plato and Aristotle helped influence this theory Problems: Retrograde motion – some planets seemed to slow down, stop, and then back up when compared to the stars Planets sometimes seemed large and close at times, and small and far away at other times 5 Early Theories Around the 2nd century AD, Ptolemy shifted the planet’s spheres so Earth was not at its center Around the 16th century, Nicolaus Copernicus suggested that the Earth and planets moved around the sun His work, The Revolutions, was published after he died and suggested his theories Copernicus’s ideas were soon called the Heliocentric Theory Copernican Revolution 6 Early Theories Copernicus’s Heliocentric Theory still had a few problems Several men contributed to his theory Tycho Brahe: built special instruments and influenced another scientist (Kepler) to determine the true shape of orbits Galileo Galilei: Observed moons orbiting Jupiter using his telescope Johannes Kepler: Successfully described planetary motion Formulated 3 laws Planets move in ellipses with the sun at the focus A planet moves faster when closer to the sun The average distance from the sun and the time it takes a planet to orbit the sun always have the same mathematical relationship 7 Early Theories Keplers 3 laws are very important to astronomers Space engineers rely on these laws to help plan space missions Aphelion: when a planet is farthest from the sun Perihelion: when a planet is closest to the sun No theory provided why a planet followed the elliptical orbit Isaac Newton Developed a mathematical law to describe gravity 8 Planets 2006, the International Astronomical Union (IAU) redefined what a planet was A body in the solar system that: Orbits Has the sun a spherical shape Does not share the space of its orbit with any other object of significant size, other than moons According to this classification, there are only 8 planets 9 Planets Dwarf Planets are objects that: Orbit Are rigid and can be nearly spherical Can Are the sun share their orbits with other bodies of similar size NOT satellites The main difference between a planet and a dwarf planet is what is around the dwarf planet 10 Planets Terrestrial Planets Planets similar in size and density to Earth Mercury, Venus, Earth, Mars Also called the “inner planets” Jovian Planets Planets larger than Earth and have low densities Sometimes called “gas giants” because they are made mainly of elements that are gases here on Earth Jovian planets have greater surface gravity because of their size and mass 11 Planets Inferior Planets Planets that orbit closer to the sun than Earth Can only be seen near sunrise or sunset Can cross in front of the sun - transit Superior Planets Planets farther from the sun than the Earth Retrograde motion 12 Planets Mercury Smallest planet Temperatures on the day side can reach 800oF, while temps on the night side can plunge to -300oF No moons Venus Opaque atmosphere Tilted 177o on its axis Highest surface temperature of any planet: 860oF 13 Planets Earth 3rd planet from the sun The most dense planet in the solar system Mars Very Has thin atmosphere 2 very small moons Contains the largest volcano in the solar system (Olympus Mons) 14 15 Planets Jupiter The largest planet in the solar system The bands are made of ammonia compounds that move around the planet The great red spot is actually a huge storm Jupiter has many moons, but the 4 largest are the most well known: Io, Europa, Callisto, and Ganymede 16 17 Planets Saturn 2nd largest planet Composition is so light, it would float in water Has an extensive ring system Has 62 moons, the largest is Titan Has a large seasonal storm called the Great White Spot 18 Planets Uranus Known for its axial tilt – 97.8o 27 known moons 13 known rings Has the blue color because of the light reflecting off the water molecules Neptune Farthest planet from the sun 13 moons, but only 2 are observable from Earth 19 20 21 Dwarf Planets Orbit the sun, spherical shape, and can share their orbit with other objects of similar size Pluto was discovered in 1929 by Clyde Tombaugh Pluto has many unique characteristics Orbital plane is tilted more than 17o to the ecliptic plane Its orbit is more elliptical than any planet Its perihelion is closer to the sun than Neptune’s perihelion Its density is much less than the terrestrial planets, but it is believed to be mostly rock and ice Forms a binary planet with its moon, Charon 22 Dwarf Planets The discovery of Eris is what spurred the change in definition Eris is almost twice as far from the sun as Neptune There are 5 known dwarf planets Pluto, Eris, Haumea, Makemake, Ceres 23 Small Solar System Bodies Asteroids The largest of the small solar system bodies Size can range from a house to 1/3 of the moon Cannot hold an atmosphere because of their weak gravity Can be oddly shaped Most asteroids have orbits in the asteroid belt (between Mars and Jupiter) Two large asteroid families lie in the same orbit as Jupiter Trojans Greeks 24 Small Solar System Bodies Comets Small solar system body made of rock and ice that orbits the sun May be chunks of frozen gas covered in gravel and dust Two parts to the comet: head and tail Two sections to the head Nucleus: solid part Coma: gaseous envelope that surrounds the nucleus The tail only forms when the comet enters the inner solar system because of light pressure 25 Small Solar System Bodies Meteoroids Meteoroids are exactly like asteroids, except in size Asteroids can be seen from Earth with a telescope, whereas meteoroids cannot Meteors A meteoroid that enters Earth’s atmosphere Friction from the air causes it to heat up and glow Meteorites Meteors that reach the surface 26 Psalm 19:1 The heavens declare the glory of God; and the firmament sheweth his handywork.