1. Chapter 1 Introduction to Astronomy

2. What is Astronomy? Astronomy is the scientific study of celestial bodies. Astrology is a group of beliefs and schools of thought that states that the relative positions of the sun, moon, stars, and other celestial bodies can provide information about a person’s personality or fate.

3. 1-1 Where Are We? Knowing where you are in space and time is critical to understanding astronomy… Your Field of View is the region you can see in an image, whether in a picture, telescope, or other type of image.

4. So What’s Out There? Moving out from the Earth we encounter many different objects…(presented in order of increasing size) Planets- Small, spherical, nonluminous bodies that orbit a star and shine by reflected light. Star- self-luminous ball of hot gas that generates its own energy. The sun is a star whose diameter is approximately 100 times larger than the Earth’s diameter.

5. Solar System- Consists of the sun, its family of planets, and some smaller bodies Galaxy- a great cloud of stars, gas, and dust held together by the combined gravity of all the matter Cluster- a group of galaxies Supercluster- a cluster of clusters of galaxies Filaments- Links of superclusters separated by voids in space Universe- contains all known objects

6. Think about this… When you look into space you are looking back in time….the light that you see left the object minutes, days, months, years, and even centuries ago! A light-year is the distance light travels in a year. If a star is 1 million light years away that means that the light that you see left it one million years ago! This is the largest measurement unit used in astronomy.

7. The sun is 1.5 x 10 8 km from the Earth (that’s 150000000 km or 150 million km!) This distance is known as 1 astronomical unit (AU). This unit is the basis for measuring most distances in our solar system. (It is smaller than a light year…)

8. The Milky Way vs. The Milky Way Galaxy The Milky Way is a band of stars visible across the night sky. This is a small band of one arm of the much larger Milky Way galaxy. The Milky Way galaxy is a spiral galaxy containing about 100 billion stars, about 80,000 light years in diameter. It is part of a cluster of galaxies that contains a few dozen galaxies and is the galaxy we live in!

9. Scientific Notation In science, we use scientific notation because.. –It makes converting between units easy –It makes it easy to write big or small numbers –All astronomical distances are expressed in metric units