How we know

We measure. We test ideas. We also enjoy stories. A story is not a fact.

• Eyes and clocks

  We watch the sky and time what moves.

• Telescopes

  Telescopes gather light so far things look brighter.

• Spacecraft

  Rockets, rovers, and probes go measure up close.

• Math

  Math checks the path before a ship flies it.

• Rocks

  Moon rocks came home. Labs tested them.

• Radio

  Beeps and pictures ride radio waves back to Earth.

Three kinds of sentence

• Measured fact

  The Sun is a star.

  Telescopes show the Sun is hot glowing gas, like other stars, only much closer.

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• Theory being tested

  There may be life we have not met.

  Scientists look for signs on Mars, on icy moons, and on far planets. We have not found aliens.

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• Story people enjoy

  The Moon is made of cheese.

  People enjoy this joke story. Moon rocks are stone, not cheese.

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