1. The Universe Around Us Geocentric = Earth-centered
Egocentric = Self-centered
Read Huygens quote (c. 1690) on page 3
Is there a center to the Universe? This should be the whole course!
We have centers of motion: Solar System, Milky Way Galaxy, clusters, etc..
Centers of motion caused by Gravity

2. Cosmic History
Big Bang Cosmology is a well accepted theory (12-16 billion years ago)
Gravity drives the formation of our Milky Way galaxy (11-14 billion years ago)
Gravity drives the formation of stars, and nuclear fusion in stars produces elements such as carbon, nitrogen, and oxygen
Our solar system formed 4.6 billion years ago.
Our Earth and the other planets in the solar system formed around our star: The Sun

3. Light Travel Time Light travels at 300,000 km/s
Astronomical distances are measured in light-years: ´ 1013 km
Stars in our sky are many light- years away
Center of the Milky Way is 28,000 light-years away
Galaxies are millions to billions of light-years away.
Observable universe: billion light-years in radius

4. The Earth Rotates

5. Relevant Geography

6. Earth Orbits Sun

7. Tilt of Spin Axis

8. The Equinoxes and Solstices
Tilt of the spin axis is related to the seasons
Effect of tilt on climate is not instantaneous

9. Cause of Seasons
The path of the Sun on Summer Solstice in the northern hemisphere
The path of the Sun on Winter Solstice in the northern hemisphere

10. Precession of the Earth’s Axis