1. The Earth in the Universe
NC Essential Standards
Created Fall 2012

2. Is the Earth round?
Technically, Earth is an oblate spheroid. It is wider around the equator than it is if you measured pole to pole.
This is caused by the rotation of the Earth on its axis.
Gravity is equal from all directions, attracting all the mass toward the center.

3. How and why does the Earth move?
The angular momentum of an object is defined relative to a fixed point. In the case of astronomy the Sun is used as the fixed point.
The main reason that the Earth has never stopped rotating since the early periods of the solar nebula is that there is nothing in the vacuum of space to stop it. The only thing that may stop the Earth’s rotation is the gravitational forces of the Sun after it begins to expand into its red giant phase. Unfortunately, there will be no life on Earth to find out.
Read more:

4. Rotation and Revolution

5. Rotation and Revolution
Recall that the Earth is tilted about 23.5 degrees on it’s axis and it turns on it once every 24 hours.
The tilt of the axis creates the seasons.
This movement also creates day and night.
Rotation also causes Earth to be a bit bigger around the equator.
The gravitational attraction between the Earth, sun and the moon creates tides.
Revolution: The Earth orbits the sun once every 365 ¼ days.

6. Precession
Change in the direction of Earth’s axis, but no change in tilt – about 12,000 years.
Changes the stars near (or not near) the Poles
Does not affect the seasons as long as the 23.5 degree tilt stays the same.

7. Nutation
Wobbling of the Earth around the precessional axis which includes a change in the angle of tilt (about a ½ degree one way or the other)
This occurs over an 18 year period and is due to the pull of the moon exclusively.
Slightly increase or decrease the amount of seasonal variation.

9. Barycenter
The barycenter is the point between 2 objects where they balance each other.
When a moon orbits a planet, or a planet orbits a star, both bodies are orbiting around a point that lies outside the larger body.
Moon does not orbit the exact center of the Earth, but a point about 1710 km below Earth’s surface.
The sun is not stationary in the solar system. It moves as the planets tug on it, but it never gets too far from the solar system barycenter.

10. How Did the Earth and the Solar System form?
The prevailing theory is the Big Bang Theory.
The universe was once in an extremely dense and hot state that expanded rapidly about 13.8 billion years ago.
Eventually, matter was gravitationally attracted to other matter, forming stars and planets, and our sun.
1929: Edwin Hubble notices that other galaxies are moving away from the Milky Way.
Background radiation is also support for this theory.

11. Where is the Earth located in the universe?
In the solar system – in one of the “arms” of the spiral shaped Milky Way galaxy.

12. Parts of the sun
The sun has a core (25% of radius), a radiative zone (30% of radius) and a convective zone (45% of radius).
The sun is composed of gas. It has no solid surface.
The two gases that make up the sun are hydrogen and helium.
Compared to other stars, our sun is medium sized and has a medium temperature. This is still VERY hot!

13. Fusion: Making Energy
Gravity pulls all of the mass inward, creating intense pressure.
The pressure is high enough to force 2 atoms of hydrogen to fuse into an atom of helium.
Heat is released during this reaction and so is radiation (in all parts of the electromagnetic spectrum). This radiation strikes Earth, helping heat the atmosphere, drive our weather, and provide energy for life.

14. Fission – breaking up nucleus of atom; leaves nuclear waste

15. Fission: a chain reaction

16. Nuclear Power: Fission Reactors