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Earth, Moon, and the Sun

The tilt makes the seasons

Summer and winter return every year. Why do they?

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The idea

Earth's axis is the line through its two poles.

Earth's axis is tilted. It keeps the same direction all year.
Step 1 of 4
  1. Earth's axis is tilted. It keeps the same direction all year.
  2. In June the north leans toward the Sun. It gets long days. It is summer.
  3. In December the north leans away. It gets short days. It is winter.
  4. The south is the other way round.

Seasons come from Earth's tilted axis as it goes round the Sun.

Earth's axis leans. In June the north leans toward the Sun. So its sunlight is stronger.

Earth is round, so the lean changes how straight sunlight falls.

The same sunlight falls on a smaller patch than in winter. That patch gets hotter.

Watch out!

Seasons do not come from Earth's distance from the Sun. Earth is nearest the Sun in January.

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This track

  1. 0 Start here
  2. 1 Earth is doing two things at once
  3. 2 The Moon keeps one face turned to us
  4. 3 When three line up, one shades another
  5. 4 The Moon shades a patch of Earth
  6. 5 Earth shades the Moon
  7. 6 Why it is not every month
  8. 7 One is safe to watch, the other never is
  9. 8 Checkpoint: motions, the Moon and eclipses
  10. 9 Why the Sun seems to move
  11. 10 Day here, night there
  12. 11 The star that stays still
  13. 12 Checkpoint: the turning sky
  14. 13 The night sky changes through the year
  15. 14 The tilt makes the seasons
  16. 15 The longest and shortest days
  17. 16 Checkpoint: the year, the tilt and the seasons
  18. 17 The big picture
  19. 18 Track quiz

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