2. Do now: If a planet has a mostly oval orbit,
Ms. Ware
Earth Science
W.O.T.D.: Eccentricity: is a measure of how an orbit
Deviates from circular. A perfectly circular orbit has an
eccentricity of zero; higher numbers indicate more
elliptical orbits
Do now: If a planet has a mostly oval orbit,
Where do you think the planet would
be fastest? Why? B A C
Sun D

3. Ms. Ware
Earth Science
10/ /09
L.T.: I can understand and calculate a planet’s eccentricity.
W.O.T.D.: Eccentricity: is a measure of how an orbit deviates from circular. A perfectly circular orbit has an eccentricity of zero; higher numbers indicate more elliptical orbits
Do Now: Ratio Review:
1.) The Sun’s diameter is 15 miles, and the planet X’s diameter is 5 miles. A student needs to draw a small model of these objects and she decides the planet should have a 2 inch diameter. What diameter should the sun have if she wants her
small drawing to remain proportional?
2.) Use the ruler on your table and draw both planet X and the sun (from above) in your notebook
(*After turn and talk to the person next to you. Show them your drawing and see if they came to the same conclusion- 2minutes)

4. Calculate the eccentricity
of the ellipse below:
length of major axis
8 miles
4 miles
Formula:
eccentricity = distance between foci
length of major axis

5. Distance between foci: 1 Length of major axis: 8
Lets try a problem!!!!
1/8= .125 MORE CIRCULAR!!!
Distance between foci: 4
Length of major axis: 12
4/12= .333….MORE ELLIPTICAL!!!

6. When does a planet move
slowest in its orbit?
When furthest
from Sun
When does a planet move
fastest in its orbit?
When closest
to Sun

7. FOCI DISTANCE= 60 mm Major Axis= 90 mm Questions:
STAR A C
Questions:
1.) What is the approximate eccentricity?
2.) As the planet moves from A to C, what happen to the
gravitational attraction?
3.) At which position does planet Q have the greatest velocity? B

8. LETS PRACTICE!!!!!

9. Explain the difference between the geo- and helio-centric
models of the solar system.
Helio-centric
Geo-centric
Earth-
centered
Sun-
centered