space

• Protostar


  Cloud of dust and gas that gradually form a star
• Star formation


  1. Gravity pulls dust and gas together

  2. Temperature rises as star gets denser

  3. Hydrogen undergoes nuclear fusion to form helium
• Main sequence star


  • Outward pressure from nuclear fusion balances inward force of gravity
  • Lasts for several billion years
• Life cycle of a small-to-medium-sized star

  1. Becomes a red giant

  2. Ejects outer layer

  3. Leaves behind a hot, dense, solid core (white dwarf)

  4. White dwarf cools to become a black dwarf
• Life cycle of a large star

  1. Undergoes more fusion and expansion/contraction

  2. Explodes in a supernova

  3. Leaves behind a neutron star or black hole
• Stars and their life cycles produce and distribute all naturally occurring elements
• Planet


  Large object that orbits a star, has cleared its neighbourhood of other objects
• Dwarf planet


  Planet-like object that orbits a star but doesn't meet all the criteria to be a planet
• Moon


  Natural satellite that orbits a planet
• Artificial satellite


  Satellite built by humans that orbits the Earth
• Our solar system is a tiny part of the Milky Way galaxy, a massive collection of billions of stars
• Orbits


  • Planets move in almost circular orbits around the Sun
  • Orbiting object is constantly accelerating and changing velocity
  • Gravitational force provides the force that creates orbits
• Orbital speed


  Faster moving objects have a smaller orbital radius
• The universe appears to be expanding, with all galaxies moving away from each other
• Evidence for universe expansion


  • Redshift of light from distant galaxies
  • More distant galaxies receding faster
• Big Bang theory


  All matter in the universe initially occupied a very small, dense, hot space that then exploded and is still expanding
• The Big Bang theory is the best current explanation, but new evidence may lead to changes in the theory
• Dark matter and dark energy are unknown substances that make up most of the universe, but their nature is still a mystery