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Summaries · Grade 7 Natural Sciences › The Sun, the Earth and the universe
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The Sun, the Earth and the universe

The Sun as a star, galaxies, light years, nebulae and exoplanets. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

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Our place in the universe

SunMercuryVenusEarthMarsJupiterSaturnUranusNeptuneNot to scale
Our solar system: Mercury closest, Neptune farthest.
  • Venus is the planet closest in size to the Earth.
  • A comet is mostly ice, dust and rock; a meteorite is a rock that strikes the Earth.
  • A constellation is only a pattern; a galaxy is a real enormous group of stars.
  • We add a leap day, because a year is about 365¼ days.
The Milky Way over the Karoo.
The Milky Way over the Karoo.
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Light years and stars

Distances in space are so big that kilometres are too small: we use light years. Stars look small because they are very far away. In the day we cannot see them: the Sun’s light is too bright. You cannot walk to Mars: space has no ground and Mars is very far.

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Astronomy

Astronomy is the study of stars and the universe. Astronomers use telescopes, often on high mountains, where less atmosphere distorts the image.

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Remember this and test yourself

Remember this: your summary
  • The Sun is an average star: neither very big nor very small. Its light takes about 8 minutes to reach us.
  • A galaxy is an enormous collection of stars, gas and dust; we are in the Milky Way.
  • A light year is the distance light travels in one year: about 9.5 trillion km (9 500 000 000 000 km).
  • Stars are born in a nebula; a star finally collapses under its own gravity.
  • An exoplanet orbits another star; gravity keeps planets in their orbits.

Write these points in your book. Read them again the night before the test.

Memory trick

A light year is a distance, not a time: how far light travels in one year. Star → galaxy → universe: like house → city → country.

Flash cards · Tap to turn over

Important words

First say what the word means, then turn the card over.

Test yourself · Part 2

True or false?

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