The solar system:

Structure of the Solar System:

  • The Sun is a star in a galaxy called the milky way.
  • The Solar system consists of the sun, planets, dwarf planets, moons, asteroids and comets.
  • Planets, dwarf planets, asteroids and comets orbit the Sun.
  • A moon orbits a planet.

The Sun:

  • The Sun formed from a cloud of dust and gas (a nebula) which was pulled together by gravity.
  • As the nebula collapsed, it became sufficiently hot and dense for nuclear fusion reactions to start.
  • In a stable star like the Sun, gravitational collapse is balanced by expansion due to fusion energy.
  • A protostar is the early stage in the formation of a star, before nuclear fusion occurs.
  • Nuclear fusion is the joining together of two smaller atomic nuclei to produce a larger nucleus. Radiation is released when this happens. Nuclear fusion happens in stars like our Sun, and in hydrogen bombs.

Orbital Motion:

  • Planets follow circular orbits around the Sun.
  • Satellites follow circular orbits around their planets.
  • Gravity provides the force that causes planets and satellites to orbit.
  • A satellite moving too quickly will leave orbit and move into space. A satellite moving too slowly will leave orbit and fall towards Earth.
  • An artifical satellite in polar orbit travels faster and with a smaller orbital radius than one in a geostationary orbit.
  • An object in a circular orbit at a constant speed is accelerating because its direction is constantly changing.
  • For an orbit to be stable, the radius of the orbit must change if the speed of the orbiting object changes.
  • The closer two bodies


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