Space Physics

• Earth's rotation


  Rotates around its axis, which is tilted 23.5 degrees from West to East and revolves around the sun in 365.25 days
• Earth's hemispheres


  Has a Southern Hemisphere and a Northern Hemisphere divided by the Equator
• Hemisphere


  Half of a sphere; Earth is divided into 2 hemispheres
• Countries at the equator do not experience season changes as the sun hits them at the same angle at all times
• Planets in the solar system


  • Mercury
  • Venus
  • Earth
  • Mars (inner, rocky planets)
  • Jupiter
  • Saturn
  • Uranus
  • Neptune (outer gas giants)
• Millions of asteroids and meteoroids are orbiting the sun, mainly found between Mars and Jupiter
• Comets


  Balls of ice, dust and gas that orbit the sun in a very elliptical orbit, leaving behind a trail of gas and dust (but the tail always faces away from the Sun)
• Formation of a solar system


  1. Molecular cloud collapses due to gravity

  2. Gasses and dust particles come together, gaining speed in a spinning motion (accretion)

  3. Disk formed by accretion (accretion disk)

  4. Gravity pulls heavier particles close together toward the centre

  5. Gasses get hot and pressurised enough to start nuclear fusion

  6. Dust particles clump together and form inner rocky planets, while gasses orbit the centre farther away and form gas giants

  7. Centre of accretion disk forms a new star (protostar), with gravity still pulling mass together
• Sun


  Makes up about 99.8% of the solar system's mass, has a strong gravitational pull keeping all the planets in orbit
• For an object to move in a circular path, a force needs to act on the object towards the centre of its orbit
• Orbits


  Elliptical, with eccentricity measuring how elliptical they are; not perfectly circular due to energy changes during orbital period
• Star pulls body of mass towards itself

  This pull generates speed, which causes the body to move away from the star (increasing speed increases the size of the orbit)
• Energy types in space


  • Kinetic Energy
  • Gravitational Potential Energy
• Planet near the sun

  Has a low Gravitational Potential Energy but a high Kinetic Energy
• Planet far from the sun

  Has a high Gravitational Potential Energy and a low Kinetic Energy
• Orbital speed formula


  Orbital speed = 2pi r/ t
• Sun


  Produces energy through nuclear fusion of hydrogen into helium, made of 75% hydrogen, 24% helium and the rest other elements, with 40% of its energy as visible light, 50% infrared radiation and 10% ultraviolet; core temperature of 15,000,000K, surface temperature of 5,800K; mass of 2x10^30 Kg
• Light year


  Distance travelled by light in one year, equal to 9.5x10^15 m
• Measuring distances using parallax


  Stars appear to move across the sky when viewed from different points on Earth's orbit; trigonometry can be used to calculate the distance between the stars and Earth
• Star life cycle (less than 8 solar masses)


  • Protostar formation
  • Stable main sequence star (fusing hydrogen into helium)
  • Red giant (fusing helium)
  • White dwarf (core collapses)
  • Black dwarf (cools down)
• Star life cycle (more than 8 solar masses)


  • Protostar formation
  • Red supergiant (fusing heavier elements)
  • Supernova (core collapses)
  • Neutron star (if core mass <3 solar masses)
  • Black hole (if core mass >3 solar masses)
• Absorption spectrum


  Dark lines in the wavelengths of visible light coming from the Sun, caused by the cool gas in the Sun's atmosphere absorbing them
• Redshift


  Shifting of light to the red end of the spectrum, caused by the Doppler effect
• Doppler effect


  Rise or fall in pitch as the source of the wave moves closer or away from the observer
• The Doppler effect is proof that the Universe is expanding and suggests that the galaxies must have been close together in the past
• Big Bang Theory


  Theory that the Universe had a beginning 13.8 billion years ago, when it was a single, unimaginably hot and dense point that has been expanding and cooling ever since
• Hubble's Law


  The speed at which galaxies are moving away from us is proportional to their distance from us, with the Hubble constant as the gradient of this relationship
• The reciprocal of the Hubble constant is known as Hubble time and can be used to estimate the age of the Universe, which is currently around 14.4 billion years