Topic 7

• Man-made satellites that have been sent into space for purposes such as satellite imaging and communications.

  Artificial Satellites
• The circular path that a satellite or planet may travel in. Since their direction is continually changing, their velocity is always changing. Gravity provides the required force for these orbits.

  Circular Orbits
• Cosmic microwave background radiation. This is electromagnetic radiation that is found in small quantities all around is. It is suggested to have come from the high energy radiation emitted by the Big Bang.

  CMBR
• The stable state of all stars. The gravitational forces pulling the star together, and the pressure pushing outwards, are balanced.

  Main Sequence Star
• A cloud of dust and gas.

  Nebula
• The radius of a body’s orbit. For a stable orbit, a change in its orbital radius is required for the body to undergo a speed change.

  Orbital Radius
• The first stage all stars go through after forming from a nebula. In this stage the star becomes hot enough for hydrogen nuclei to fuse.

  Protostar
• When their hydrogen is used up and larger nuclei are produced by fusion, stars of a similar magnitude to the Sun will expand to form one.

  Red Giant Star
• A rejected theory of the origin of the universe. It suggests that the universe has always existed, is continually expanding, and is continually producing mass. It can account for the red-shift but cannot explain CMBR.

  Steady State Theory
• A star formed from a cloud of dust and gas being pulled together by gravitational attraction. Fusion reactions occur in it.

  Sun
• The explosion of a massive star, that distributes the elements created by the fusion reactions in the sta, throughout the universe.

  Supernova
• The force of matter due to gravity. It is equal to the product of mass and gravitational field strength, and so varies depending on your location in the universe.

  Weight
• When the fusion reaction in stars of a similar magnitude to the sun come to and end, the star will contreact under gravity and eventually cooled won to form one.

  White dwarfs
• The observed increase in the wavelength of the light emitted by distant galaxies. The more distant the galaxy, the faster it is moving and so the bigger the observed increase in wavelength.

  Red-Shift