Topic 1: Planet Earth

• The Earth's atmosphere is mostly made of nitrogen and oxygen
• Crust: 0-70km

  Mantle: ~80% of the Earth's volume

  Outer core: ~5000K, made of liquid iron and some nickel, the charged particles that flow in the outer core are responsible for the Earth's magnetic field

  Inner core: ~5500K, high pressure prevents iron and nickel from melting
• Latitude is measured north or south of the equator

  Longitude is measured east or west of the Prime Meridian
• The Earth's polar axis is tilted at 23.5 degrees to the 'vertical'
• Spring equinox is on March 21st, Autumn equinox is on September 23rd
• The Summer solstice is on 21st June, the Winter solstice is on 21st December
• Our atmosphere provides us with oxygen to breathe, absorbs harmful solar UV and X-radiation, regulates the planet's temperature to a mean of 15 degrees and protects us from most meteoroid strikes
• Our atmosphere affects astronomers by:

  • the sky being blue which limits observations to nighttime
  • the air in the atmosphere is continuously in turbulent motion causing the stars to appear to twinkle
• Light is scattered by oxygen and nitrogen molecules in our atmosphere; most scattering occurs at the shortest (blue) wavelengths, so the sky is predominantly blue
• Turbulent motion: different densities of air rise and fall on a variety of scales, causing light to refract and change direction as it passes through the different layers
• Light pollution:

  • Skyglow is a rusty orange haze cast by lights near urban areas
  • Local glare from things such as streetlight that ruin our eyes night vision (dark adaptation)
• The Earth is the largest terrestrial planet with a mean diameter of 13000km
• The Earth is an oblate spheroid, meaning it is slightly flattened at the poles.