Grade 6

Earth and Space

Six lessons that move outward from the shape of the Earth to the whole solar system, so that day and night, the seasons, the phases of the Moon and eclipses all turn out to come from the same few motions.

6 lessons

  1. 1How can anyone tell the Earth is round without going to space?From a few observations anybody can make. A ship sailing away vanishes from the bottom upwards rather than shrinking to a dot. At the very same moment, a stick casts a different shadow in two distant places. And during a lunar eclipse the shadow the Earth throws onto the Moon is always round, from every direction.25m
  2. 2If the Earth spins eastward, why does the Sun rise in the east?Precisely because of that. As we travel eastward, places to the east come into the Sun's light before we do, and we turn towards it. From where we stand it looks as though the Sun is climbing out of the east, but it is not moving at all — the ground beneath our feet is.30m
  3. 3Is summer hot because the Earth is closer to the Sun?No. The simplest evidence is that Australia has summer exactly when Israel has winter, and both are on the same ball at the same distance from the Sun. What decides it is the tilt of the axis: in summer the Sun's rays strike the ground steeply, concentrating more energy into a smaller area, and the daylight hours are longer.35m
  4. 4Why does the Moon change shape — is it the Earth's shadow?No. The Sun lights exactly half the Moon at every moment. What changes is how much of that lit half we can see from here, and that depends on where the Moon is in its orbit around us. The Earth's shadow does fall on the Moon sometimes — but that is a lunar eclipse, a few times a year, not every month.30m
  5. 5If the Moon goes round us every month, why is there not an eclipse every month?Because the Moon's orbit is tilted by about five degrees compared with the Earth's path around the Sun. In most months the Moon passes a little above the line or a little below it, and the shadow misses. Only when it crosses the plane at exactly new or full Moon do the three really line up.30m
  6. 6What holds the planets in their orbits?One force only — gravity. The Sun pulls every planet towards it, and the planet moves forward fast enough to keep falling around the Sun instead of into it. The same force holds the Moon around the Earth. An orbit is nothing more than a fall that never reaches the ground.35m