GCSE Astronomy - Planet Earth

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  • Created by: Erin
  • Created on: 27-03-13 15:38

How the Earth is recognised

  • Water Surface!
  • Atmosphere!
  • Life!
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Why is the sky blue?

The Earth's atmosphere causes the light from the Sun to scatter, which means we only see the blue light.

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What are the benefits of the Earth's atmosphere?

  • It blocks out most of the ultra-violet rays, infra-red radiation and X-rays.
  • Gives us atmospheric pressure.
  • It traps heat from the Sun and keeps Earth warm.
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What is the main cause of light pollution?

  • The main cause of light pollution is HUMAN ACTIVITY (street lights, lights from houses etc)
  • Astronomers do not like this because it obscures their vision of the stars and other objects in the Solar System, meaning that for accurate observations they must set up telescopes outside the Earth's atmosphere.
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Eratosthenes and the circumference of the Earth


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Diameter of the Earth and other planets

  • Mercury - 4900km
  •  Venus - 12,100km
  • Earth - 12,800km
  • Mars - 6800km
  • Jupiter - 143,000km
  • Saturn - 121,000km
  • Uranus - 51,000km
  • Neptune - 50,000km
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Evidence that the Earth is spherical

Aristotle first discovered that the Earth is spherical. He did so, firstly by watching a ship on the horizon. The ancient Greek skies were much clearer than our skies today so he could see that when the ship reached the horizon, the bottom of it began disappearing as though it was going downhill. If the Earth was indeed flat, he would still see the whole of the ship. His second piece of evidence was how the constellations appeared to move around the sky at night. If the Earth was flat, the Earth would not turn and the constellations would not move. His third piece of evidence was looking at the shadow of the Earth on the Moon at a lunar eclipse. It cast a round shadow on the Moon, rather than a straight shadow, proving that the Earth is round.

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Important Astronomical terms

  • Equator - The imaginary line around the middle of the Earth that is of equal distance to the North pole and the South pole.
  • Latitude - The angular distance of a place north or south of the equator.
  • Longitude - The angular distance of a place east or west of the Earth's meridian at Greenwich.
  • Poles - The points that the axis of rotation of the Earth pass through.
  • Horizon - The imaginary line where the sky and the Earth meet.
  • Zenith - The point directly above us in the sky.


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www.astronomygcse.cf has revision powerpoint and all the past papers

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