1. The Scale of the Cosmos The following photographs are from Chapter 1 in the textbook. Each picture zooms out 100 times from the previous one.

2. On the ground… About the width of a hair About the width of your palm

3. By continuing to zoom out, we move from a boxing ring to a large city, to a seacoast around 60 miles across. But further zooms take us away from the earth itself.

4. It takes light 3.3 seconds to travel one million km.

5. Distances in the Solar System are measured in Astronomic Units (AU), the average distance from the Earth to the Sun (93 million miles). Earth 1 AU 10 AU

6. As you zoom out of the Solar System, distances can be measured in light years, the distance light travels in one year (~ 6 trillion miles)!

7. On these scales, the Sun and its planets are insignificant in size. The Milky Way Galaxy is around 100,000 light-years across. You are here!

8. A Universe of Galaxies!

9. To the Beginning of Time! This is the background radiation left over from the Big Bang.

10. Two terms to remember: 1 Astronomic Unit (AU) = the distance from the Earth to the Sun (around 93 million miles) 1 light-year is the distance traveled by light in one year (around 5.9 trillion miles)

11. CONSTELLATIONS

12. Are they real? Each culture has different names for the constellations. The patterns are very arbitrary, and often defy explanation. Now that we can determine distance to stars, we can see that they are not actually grouped together, but many light-years apart. Today, we only use them to orient ourselves in the sky.

13. The Northern Sky

14. THE SUMMER SKY

15. The Autumn Sky

16. The Sky in Winter

17. Spring Constellations

18. Why have constellations today? Astronomers have agreed that the sky will be divided into 88 sections. These are the modern constellations. They do not look like mythical figures, just boundaries, like states or counties. The large galaxy M31 gets its common name because it is inside the border of the constellation Andromeda.