The Universe Around Us

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 0.946 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 12-16 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 Earths Axis