1. Eccentricity,Axial Tilt, Precession and Inclination

2. Eccentricity
Distance between 2 foci divided by the length of the major axis
Tells you about the shape of your ellipse
An eccentricity of 1 would be a flat line (high eccentricity= more oval shaped)
An eccentricity of 0 would be a perfect circle (low eccentricity= more circular)

3. Kepler’s First Law
The orbit of each planet around the sun is an ellipse with the sun at one focus of the ellipse.

4. Kepler’s Second Law
As a planet moves around the sun in its orbit, it covers = areas in = times

5. Kepler’s Third Law
The time it takes a planet to complete 1 orbit is related to it’s average distance from the sun

6. Earth’s eccentricity is .017
Planets’ orbits
Mercury has the most elliptical orbit, it is closest to the sun (eccentricity of 0.2)
Earth’s eccentricity is .017
Earth’s eccentricity changes slightly as a result of the weak gravitational pull of other planets

7. Axial Tilt (obliquity)
Earth’s axis is tilted at 23.5 degrees
Axial tilt varies over a 41,000 year cycle
Ranges from
Greater tilt= greater temp. differences between summer and winter

8. Seasons Winter occurs when a hemisphere is tilted away from the sun
Earth is currently closest to the sun in it’s orbit during winter

9. Precession 2 parts -Part 1
Axial precession- the rotation of earth has a slight wobble
Caused by differences in gravitational pull of moon and sun on earth
Complete cycle of this wobble is 25,725 years
As it wobbles the timing of the seasons changes

11. Precession Part 2 orbital precession
The orbit of earth itself rotates very slowly around the sun as well

12. Precession of the equinoxes
Together axial and and orbital precession are called precession of the equinoxes
A complete cycle of this combined effect occurs approximately every 22,000 years.
Halfway through this precession cycle the Northern hemisphere’s winter will be from June to September!

13. Poster Time!
Create a poster showing the position of earth and the sun when it is summer here.
- Then draw a picture showing the position of the earth and the sun when it is winter here
On your poster label the following:
-Sun
-Colorado
-Earth’s tilt (how many degrees)
Color it!
Somewhere on your poster explain….
Why we have different seasons where we live
Why places near the equator do not have different seasons
Why our summer months are Peru’s winter months

14. Inclination Planes- a flat 2 dimensional surface
Orbital plane- narrow range in which planets orbit the sun.

15. Asteroid and comet planes
Found mainly in the solar system beyond earth between Mars and Jupiter
Few are found in the inner solar system
Asteroids occupy very little space

16. Comets Comets have highly elliptical orbits
- As they move closer to the sun in their orbit the icy mix that makes up their nucleus turns to gas and streams away.
-Results in the tail you see called a coma
- When it moves further away from the sun the ices are no longer turned to gas

17. Comets
Comets are loners that periodically enter the inner solar system
Comets have a high inclination
Their orbits are highly eccentric
Collision with the comet's nucleus could be bad but a collision with the tail would do little damage because it’s mostly gas

18. Collisions? Asteroids orbits are highly elliptical
Have a slight inclination to their plane (paths around the sun are tilted compared to earth’s)
As earth orbits the sun it can cross the path of asteroids orbits
Astronomers search the sky for asteroids and map their orbits so they know of potential threats ahead of time