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EARTH & SPACE Celestial Objects THE UNIVERSE The universe includes everything that exists. This includes celestial objects such as stars and planets, plus all the matter and empty space surrounding them. Copyright © 2010 McGraw-Hill Ryerson Ltd. Our Solar System The solar system is a system of planets, including Earth, moons, and other objects, that orbit the Sun. An orbit is the circular (or elliptical) path of one object around another object. The gravitational pull (a force of attraction between two masses) between the Sun and the planets keeps the planets revolving around the Sun. Copyright © 2010 McGraw-Hill Ryerson Ltd. Stars and Their Characteristics A star is a massive ball of superheated gases that radiates heat and light. Characteristics used to describe stars include: • size • colour • temperature • and density Copyright © 2010 McGraw-Hill Ryerson Ltd. Galaxies: Collections of Stars A galaxy is a collection of billions of stars, plus gas and dust, held together by gravity. There are billions of galaxies in the universe. Our solar system is located in a galaxy called the Milky Way. Copyright © 2010 McGraw-Hill Ryerson Ltd. Distances in Space Distances in space are so large that well-known units such as kilometres are almost meaningless. To measure the immense distances in space, astronomers have created a unit called the astronomical unit (AU). 1 AU is equal to the distance between Earth and the Sun, which is about 150,000,000 km. Copyright © 2010 McGraw-Hill Ryerson Ltd. Distances Involving Galaxies Distances involving galaxies are much larger than those involving solar systems. Instead of using AUs, scientists use a unit called a light-year, which is a measurement equal to the distance that light travels in one year. With light travelling at 300 000 km/s, one light-year is equal to about 9 500 000 000 000 km (9.5 x 1012km). Copyright © 2010 McGraw-Hill Ryerson Ltd. Classifying Galaxies Galaxies come in many different sizes and shapes. Bill Nye - Outer Space Copyright © 2010 McGraw-Hill Ryerson Ltd. Topic 3.1 Review Key Concepts to be reviewed: • We see stars that we organize into patterns. •We see celestial objects of the universe. •We see objects separated by immense distances. Copyright © 2010 McGraw-Hill Ryerson Ltd.