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Earth, Moon, and the Sun

Why it is not every month

New Moon comes every month. So why is there no eclipse every month?

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The idea

Earth's path round the Sun.
Step 1 of 4
  1. Earth's path round the Sun.
  2. The Moon's path, tilted a little against it.
  3. Most months the Moon sits above or below the line.
  4. So the shadow misses Earth and goes into empty space.

The rule

Tilt is measured in degrees, written °.

The Moon's path is tilted about 5°. At most New Moons, its shadow misses Earth.

The Moon's path crosses Earth's path at two points. Twice a year the Sun lines up with them. Those times are called eclipse seasons. A New Moon then can cast its shadow on Earth.

The same tilt explains why lunar eclipses are not monthly.

Jump to lesson

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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