Space Physics - Key Terms

• Universe

  all existing matter, energy and space
• Galaxy

  a collection of millions / billions of stars held together by gravitational attraction
• Nebula


  a cloud of particles and gases
• Protostar


  the hot dense mass that forms when a nebula collapses, which evolves into a star once nuclear fusion can occur
• Main sequence


  a stable period in the lifecycle of a star, during which the outward acting fusion energy and inward acting force of gravity are in balance
• Supernova


  a large star that explodes because the forces within it are no longer balanced / stable, releasing vast amounts of energy
• Orbit


  the curved path followed by a planet, satellite, comet, etc. as it travels around a body that exerts a gravitational force upon it; also applies to the paths of electrons around a nucleus (which exerts an electrostatic force of attraction)
• Circular motion


  produced when an object rotates with a constant speed but changing velocity; the instantaneous velocity is perpendicular to the centripetal force
• Body


  an object that has three dimensions and mass
• Red-shift


  the observed increase in the wavelength of light from distant galaxies, towards the red end of the spectrum