P6: Space physics

  1. The solar system

  • consists of:

    • the sun

    • eight planets: mercury, venus, earth, mars, jupiter, saturn, uranus, neptune

    • dwarf planets: pluto

    • asteroids and comets

    • moons: natural satellites

  • light speed: time = distance/speed of light

  • gravitational field strength

    • the greater the mass of a planet, the greater the strength of gravitational field at its surface

    • the greater the distance, the weaker the gravitational field strength

  • orbital attraction of the sun

    • sun’s gravitational attraction keeps planets in orbit

    • force is directed from the orbiting object to the centre of the sun

    • as distance increases → gravitational field strength and speed decreases

    • the sun’s gravitational attraction allows objects to maintain a centripetal force

      • centripetal force is proportional to its orbital speed

    • equation: v = 2πr/T

  1. The sun as a star

  • the sun is a medium-sized star

    • consists of hydrogen and helium

    • radiates energy in infrared, visible and UV on the electromagnetic spectrum

  • stars undergo nuclear fusion of hydrogen nuclei to form helium nuclei that make them stable → releases a huge amount of energy

  • the universe: a large collection of billions of galaxies

  • galaxies: large collection of billions of stars

  • the milky-way is one of billions of galaxies making up the universe

    • the sun is one of billions of stars that make up the milky way

  • one light-year: the distance travelled by light in one year

    • one light year = 9.5 × 10^12 km or 9,5 × 10^15 m

  • star formation: nebula → protostar → stable star

    • nebula: giant interstellar cloud of gas and dust

    • protostar: ball of hot gas pulled together by the gravitational attraction within a nebula

      • density increases and particles are pulled closer

      • results in more frequent collisions → temperature rises

    • stable star: when protostar is hot enough, nuclear fusion occurs within its core → stable star

      • star is in equilibrium

      • gravitational forces act inwards

      • thermal pressure acts outwards

  • life cycle of a star: based on mass

    • low mass star: red giant → planetary nebula → white dwarf

    • high mass star: red supergiant → supernova → neutron star

    • very high mass star: red supergiant → supernova → black hole

  • doppler effect of light: if light moves towards the observer → the observed wavelength decreases

  • the big bang theory

    • the universe began from a single point that was extremely hot and dense

    • galaxies are moving away from us → universe is expanding

    • the universe is approximately 13.8 billion years old