Astronomy Chapter 1: Here and Now • You surveyed the universe by taking a cosmic zoom in which each field of view (region you can see in the image) was 100 times wider than the previous field of view. • Astronomers use the metric system because it simplifies calculations and use scientific notation for very large of very small numbers. • You live on a planet , Earth, which orbits our star , the sun, once a year. As the Earth rotates once a day, you see the sun rise and set. • The moon is only one-fourth the diameter of Earth, but the sun is 109 times larger in diameter than Earth – a typical size for a star. • The solar system includes the sun at the center and all of the planets that orbit around it – Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. • The astronomical unit (AU) is the average distance from Earth to the sun. Mars, for example, orbits 1.5 AU from the sun. The light-year (ly) is the distance light can travel in one year. The nearest star is 4.2 ly from the sun.
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