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The Solar System

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Formation of the Solar System

  • Began as a nebula 4.5 BYA
  • Rotation is amplified as the nebula collapses into a dense gas cloud-angular momentum is conserved
  • Gravity continues to pull the gas and dust together increasing the density at the center creating a protostar
  • Temperature at center continues to increase until it is hot enough to ignite the fusion of hydrogen atoms
  • Debris further out in the disc begin to clump together into protoplanets
  • Early solar system looked different than today, outer planets were closer to the sun but were pushed outward because of interactions with smaller bodies
  • Our solar system is now thought to be relatively stable and unlikely to change until the sun begins to run out of hydrogen Video Clip

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Evidence

  • All planets orbit in the same direction the sun rotates
  • All planets orbit within a few degrees of the Sun’s equatorial plane
  • Larger gas planets have a similar composition to the sun
  • Images of young stars show many are circled by disks of dust and gas

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What Does Our Solar System Consist of?

  • Made up of the Sun, eight planets, a number of dwarf planets, and smaller objects such as comets and asteroids
  • Planets-orbit the sun, have enough gravity to form a sphere, and sweep their orbit clear of debris
  • Dwarf Planets-not large enough to sweep their orbits clear of debris
  • Terrestrial Planets-4 inner planets that have rocky surfaces

Mercury - Venus - Earth - Mars

  • Gas Giants-4 outer planets which consist mostly of hydrogen, helium and various other gases like methane

Jupiter - Saturn - Uranus - Neptune

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Orbits

  • Gravity causes all planets to fall towards the Earth as they also move sideways relative to the sun → Result is that they trace elliptical paths around the sun
  • Johannes Kepler (1571–1630) was a German astronomer who spent years looking at planetary data and came up with Kepler’s Laws

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Kepler’s Laws

  • Kepler’s 1st law - an orbit is in the shape of a slightly flattened circle, or ellipse. The eccentricity of an ellipse describes how “flattened” it is. A circle has an eccentricity of 0, and a flat line segment has an eccentricity of 1.
  • Kepler’s 2nd law - a planet speeds up as it gets closer to the Sun, and slows down as it moves farther away.
  • Kepler’s 3rd law - describes the relationship between a planet’s orbital radius (R), or its mean distance from the Sun, and the planet’s period (T), or amount of time to complete an orbit. R3=T2