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Chapter 1

AST101-Chapter 1.txt

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University of Toronto Mississauga
John Lester

Chapter 1 Where is earth? 1. Earth is a member of the solar system. 2. Earth is not the center of the solar system. 3. Earth is not the center of the whole universe. 4. It was believed (without proof) that earth was the center of the universe f rom the time of Greek Astronomy (2300 years ago) until about 1500. 5. In fact, Earth is insignificant, except that we live here. What is the Solar System? 1. Solar system = the Sun and all the objects that "belong" to the Sun - a lar ge family. 2. The solar system formed billions of years ago. 3. There are many other "solar systems", far beyond our System. 4. We cannot visit these other systems because they are far away. Members of the Solar System 1. Sun = heart/centre of the Solar System - but it is just an ordinary star, l ike billions of others. 2. Earth is NOT the centre of the solar system or universe. 3. Major planets, like Earth, Mars, J ▯¦piterâ 4. Dwarf planets, like Pluto, Eris,... 5. Natural satellites (moons) orbiting planets. 6. Minor planets = asteroids. 7. Comets. 8. Meteoroids (=rocks), ice, dust. How "big" is the Solar System? 1. Words, like "big", do not have enough information. We need to use numbers. 2. Do NOT memorize numbers for this course. 3. Learn HOW we know the number. 4. Learn what the number MEANS. 5. Understand what would be different if the number were different. Be a quest ioner. How "big" is Earth? 1. Earth's radius = 6,378 km or Earth's diameter = 2 x radius = 12,756 km. 2. Numbers have units, such as km. 3. The value is NOT important, but: * - how did we learn Earth's radius? * - what does Earth's radius tell us? * - what would change if Earth had a different radius? Numbers in ratios Ratios compare two numbers. One value is a multiple or fraction of another value , more informative than the "pure" number. Example: Radius of Moon / Radius of Earth = 1738 km / 6378 km = 0.272 OR Radius of Moon = 0.272 x Radius of Earth NOTE: Ratios have no units. Numbers in Scientific Notation 1. Numbers can be "astronomically" large or small. 2. It is easier to write very large (and very small) numbers in scientific not ation. 3. Example: the distance from Earth to Sun is 150000000 km = 1.5 x 108 km. Numbers using new units 1. Familiar units, such as km, are too tiny for astronomy. 2. Invent new units t
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