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Chapter 14: The Solar System

Difficulty Level: At Grade Created by: CK-12
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There's no place like home.

Our solar system is enormous, with dwarf planets in orbit around the Sun tens of thousands of times further away than Earth. It took astronauts three days to get to our nearest neighbor, the Moon, and would take about six months each way for people to get to Mars and back. This image was the first ever taken that had Moon and Earth in the same frame, and it wasn't until 1977, when Voyager I was 7,250,000 miles away. But compared to the Milky Way Galaxy, the solar system is just a cozy little spot in a big world. There are lots of planets and lots of stars and lots of galaxies, but our planet is different. It is one (maybe one of many) that has intelligent life.

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Chapter Summary


At the center of the solar system is our star, the Sun. Solar energy is the result of the fusion of hydrogen and helium. The Sun is not just a featureless ball of gas, but has three internal layers and an atmosphere. We see the surface features, like sunspots, which have an affect on Earth. Eight planets orbit the Sun; the small, dense, rocky four nearer the Sun, and the large, gaseous four further away. Mercury is the smallest planet; it is closest to the Sun so it is extremely hot in most locations. Venus, the second planet out and the closest to Earth, has a thick, carbon dioxide-rich atmosphere with a large greenhouse effect and so is also very hot. Earth, the third rock from the Sun, is the only one of the inner planets with a large moon. The red planet, Mars, is the most earth-like, with channels where water once flowed and large volcanoes. The four gas planets — Jupiter, Saturn, Uranus, and Neptune — are composed of hydrogen, helium, and some methane and other gases. All have rings and moons. The other objects in the solar system are the five dwarf planets, which include Pluto, plus the asteroids, and comets. An object that strikes Earth is a meteorite. Increasing numbers of planets are now being found in other solar systems; they are called extrasolar planets or exoplanets.

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Difficulty Level:
At Grade
Date Created:
Nov 05, 2015
Last Modified:
Dec 15, 2016
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