space

• Red-shift is an observed increase in the wavelength of light from distant galaxies
• The further away a galaxy is, the faster it is moving
• The further away a galaxy is, the greater the observed increase in wavelength
• Red-shift provides evidence that the universe is expanding and supports the Big Bang theory
• The Big Bang theory suggests that the entire universe started from a very small, hot, and dense region in space
• When comparing the observed red-shift of two galaxies, the one further away is traveling faster and has a greater observed red-shift
• Scientists observed supernovae to provide evidence that the universe is expanding at an ever faster rate, suggesting galaxies are moving away at an ever faster rate
• Prior to observations of supernovae, it was believed that the rate of expansion of the universe would occur at an ever slower rate due to gravitational forces
• Ideas like dark matter and dark energy could explain the universe's ever-increasing rate of expansion, but these concepts are still being developed by scientists and are not yet fully understood
• Our solar system is part of the Milky Way galaxy
• There are eight planets in our solar system, plus the dwarf planets
• The planets in our solar system orbit around the sun, which is a star
• The gravitational force of attraction pulled together the cloud of dust and gas to form the Sun
• A cloud of dust and gas is described as a nebula
• Fusion reactions take place at the start of a star’s life cycle as dust and gas is drawn together
• The size of the star determines the type of lifecycle it undergoes
• All stars of the same or greater size than the sun undergo the protostar phase and the main sequence phase
• Stars of a similar magnitude to the sun become black dwarfs at the end of their life-cycle
• Stars much bigger than the sun can become neutron stars or black holes at the end of their lifecycle
• Stars of similar size to the sun go through the red giant and white dwarf phases between being a main sequence star and a black dwarf
• Two phases stars of greater size than the sun go through between being a main sequence star and a neutron star/black hole:

  1. Red supergiant

  2. Supernova
• Elements heavier than iron are produced in a supernova
• Nuclei of hydrogen fuse together to form heavier elements in a star
• Elements are distributed throughout the universe through the explosion of a massive star (supernova)
• For a stable orbit, the radius must change if the speed changes because:

  • At higher speeds, the object requires a greater centripetal force
  • For a greater centripetal force, the gravitational force must increase
  • This is achieved by the radius of the orbit being reduced
• To maintain a circular orbit, gravity provides the gravitational force that acts as the object’s centripetal force, allowing the object to maintain its circular orbit
• A planet’s moon can be described as a natural satellite
• Examples of artificial satellites:

  1. TV satellites

  2. Satellites used for satellite imaging
• The force of gravity acting on a satellite can alter its velocity since the direction is continually changing, but it can't cause a change of speed since there is no force component in the direction of motion
• Star at the centre of our solar system

  The Sun
• Planets in our solar system

  Eight (and several dwarf planets)
• Natural satellite of a planet

  A moon
• Galaxy our solar system belongs to

  The Milky Way galaxy
• How a star forms

  1. A cloud of dust and gas (called a nebula) is pulled together by gravity

  2. As it collapses the temperature rises. This is called a protostar

  3. Eventually the core of the protostar is hot enough to start fusion

  4. The star joins the main sequence
• Why stars are stable


  • There is an equilibrium between gravitational forces pulling in and radiation pressure (forces due to fusion energy) pushing out
• Type of star our Sun is

  A main sequence star
• Future life of our Sun

  1. In about 5 billion years, when it has used the hydrogen in its core it will swell to a red giant

  2. It will fuse helium in its core

  3. Later it will shed its outer layers leaving behind the hot core… a white dwarf

  4. This will very slowly cool to become a black dwarf
• Red giant


  A large cool star. It is formed when a main sequence star has used all the hydrogen in its core and starts to fuse helium instead
• Future life of a large main sequence star

  1. It will swell to a red supergiant

  2. It will fuse helium and heavier elements (up to iron) in its core

  3. It will then explode catastrophically (a supernova)

  4. The remains of the core will form a neutron star or (for the largest stars) black hole
• Red supergiant


  A very large cool star. It is formed when a large main sequence star has used all the hydrogen in its core and starts to fuse helium and heavier elements instead