EAR118 The Earth in space

EAR118 The Earth in space

1. General statistics

   • Average distance between stars = 30 x 10^12km (3 light years)
   • Approximately 200 x 10^9 'Suns' in the Milky Way Galaxy
     • + billions of galaxies
   • Distance between planets measured in kilometers/ astronomical units
     • 1 astronomical unit (AU) = 1.496 x 10^8km
   • Relative distance of planets from the sun in AU
     • Mercury = 0.39
     • Venus = 0.72
     • Earth = 1.00
     • Mars = 1.52
     • Jupiter = 5.20
     • Saturn = 9.54
     • Uranus = 19.19
     • Neptune = 30.06
     • Pluto = 39.53
     • Inner
     • Outer
   • Speed of light = 300,000kms^-1
     • takes 5 1/2 hours to reach Pluto
   • Earth diameter = 12,756km
     • Sun diameter = 1.4 x 10^6km
       • The sun can hold the earth 1.3 x 10^6 times

2. Key figures

   • Nicolaus Copernicus (1473-1543)
   • Tycho Brahe (1546-1601)
   • Jahannes Kepler (1571-1630)
     • Coined Kepler's 1st, 2nd and 3rd law
   • Isaac Newton (1642-1727)
     • Coined Newton's 1st, 2nd and 3rd law of motion
   • Milutin Milankovitch (1879-1958)
     • Serbian astrophysicist
     • Coined the Milankovitch cycles

3. Laws/theories

   • Kepler's first law
     • Planets go round the sun in an elliptical orbit (Oval shaped)
     • Eccentricity (e)
       • e=0 Perfect circle
       • e=0.99 Oval
     • Pluto e=0.25
     • Earth e=0.017
   • Kepler's second law
     • A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
   • Kepler's third law
     • The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.
       • p^2/a^3 = Constant
         • P = period in years
         • a = semi-major axis in AU
   • Newton's first law of motion
     • If the net force is zero then the velocity of the object is constant.
       • e.g. the Earth remains in the sun's orbit without moving towards or away from it
   • Newton's second law of motion
     • F=ma
       • Force = mass x acceleration
     • M(Sun) A(Sun) = M(Earth) A(Earth)
       • This is the reason why the Earth orbits the sun and doesn't move away/towards it
     • Plane of the eliptic - plane planets follow around the sun
       • 7 planets hav orbits close to the eliptic plane
         • Exceptions include Mercury (inclined at 7deg) and Pluto (Inclined at 17deg)
   • Newton's third law
     • Every action has an equal and opposite reaction
       • When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

4. Insolation

   • Amount of incoming solar radiation per unit area of the Earth's surface
     • Major control of short and long-term climate
     • Hence why warmer climte on equator and colder at the poles (Solar radiation much more direct)

5. Longer-term cycles

   • Cyclic variation in 3 ways
     • Eccentricity
       • Oval/circle orbit
     • Obliquity (tilt)
       • tilt of poles has varied from 21.5deg to 24.5deg
         • Current rotation axis - 23.5deg
     • Precession
       • 'wobble' of axis (direction poles face)
     • Results in variation in solar energy reaching Earth

6. Other important controls on climate

   • Continental positions
   • Uplift of continental blocks
   • Variations in atmospheric CO2