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Summary of week 1: Preview: Some basic astronomical objects and their approximate size scales Planet (ex.: Earth) An object held together by its self-gravity, in orbit about a star, that has insufficient mass to become a star (< 80 Jupiter masses) or a brown dwarf (< 13 Jupiter masses). Brown dwarf: A “failed star”, that is, an object more massive than a planet, but insufficient to become a star. These objects typically have fusion reactions involving deuterium early in their life cycle, but never fuse ordinary hydrogen. Planetary system (Solar System) One or more stars, gravitationally-bound together, plus their associated planets, moons, asteroids, comets, etc. 144 planetary systems are known (Sept 9, 2005), including 168 planets and 18 multiple systems. Stars (The Sun) – A self-luminous, gravitationally-bound ball of gas that shines (or used to shine) because of nuclear fusion reactions in its core. Galaxies (The Milky Way) A large (typically 5000-200,000 ly) gravitationally-bound system of hundreds of millions (or up to a trillion) of stars. The Milky Way is about 100,000 light years across and has over 100 billion stars. Clusters of Galaxies (The Local Group) Superclusters of galaxies (The Virgo Supercluster) Quasar: A star-like, extremely luminous object billions of light years away. Located in the core of a larger galaxy. The Visible Universe: The part of the Universe that can be observed from the Earth at the present time. Note: This is not a fixed volume, and some objects currently outside our visible universe may be within it in the future. The Universe: “All that there is (was; will be)” Astronomical Unit: The average distance of the Earth from the Sun’s center. 1.50 x 1011m. Light year: The distance light travels in a year. About 10 trillion km. Time scales: Universe: 15 billion years Milky Way Galaxy: 14 billion years Solar System: 4.6 Billion years Unicellular life: 3.4 billion years (oldest fossils) Cambrian era: 600 million years (fossils of complex, hard-bodied animals) Dinosaurs: 65-250 million years Homo sapiens: about a million years If 15 billion years = 1 day, humans appeared about 6 seconds ago! History of Astronomy (Chapter 1): Know who the following were and what their key discoveries or contributions were: Copernicus, Tycho Brahae, Kepler, Galileo, Newton. Know Kepler’s 3 laws of planetary motion. Most of what you need to know about Newton is coming up in Chapter 2. (over) Class participation: of the 5 points that this is worth, one point will be for each of the following two items 1) Some time before the midterm exam, come to my office hours. Even if you have no questions, come and chat for a minute or two with me, because I want to know who you are, what you are studying, how you are doing in the class, etc. 2) Make a brief presentation to the class (say, about a minute) based on one of the astronomy picures of the day (see link on class web site). Choose an object that interests you, show it to the class and explain what it is and some of its basic properties. Mention things that make sense and are relevant. For example, where it came from or what it is doing now. You might want to mention distance, temperature, mass, composition, etc, depending on the object. If you prefer, you can briefly describe an astronomy-related newspaper article on a recent discovery. We should have about 3 such presentations per week, scheduled by the week. First quiz: Wednesday Sept 14 on the preview, appendix, items on the front of this sheet, and key parts of Chapter 1. First lab: We will door the indoor lab, making spectroscopes and telescopes. You don’t need to bring your star and planet finder, but please bring your lab manual part I. Week 2: Gravity and Motion Pay special attention to the concepts of inertia (mass), acceleration, velocity, and force. Know Newton’s three laws of motion.