Learning Exercise

CA Earth Science Standard: 1 Astronomy and planetary exploration reveal the
solar system’s structure, scale, and change over time. As a basis for
understanding this concept: a. Students know how the differences and
similarities among the sun, the terrestrial planets, and the gas planets may
have been established during the formation of the solar system.

ENGAGE
Use Merlot sites:
Your Age On Other Worlds http://www.exploratorium.edu/ronh/age/
Your Weight On Other Worlds http://www.exploratorium.edu/ronh/weight/index.html

EXPLORE

Students complete a data table based on the internet resources and compare with
lab partners.


EXPLAIN
(Prentice Hall, Earth Science, 2006, page 617-621, optional)

Background Information
Vocabulary:
Rotation (rates) revolution (rates) eccentricity
major axis minor axis foci
perihelion aphelion astronomical unit
weight mass


Keppler’s 3 Laws:
1. Each planet orbits the Sun in a shape called an ellipse.
2. As a planet orbits, it covers equal amounts of area in equal amounts of time.
3. Mathematical formula, the square of the length of time it takes a planet to
orbit the sun (orbital period) is proportional to the cube of its mean distance
from the sun. (Period2 = Distance3)


Theory of Gravitation (Newton):
Every body in the universe attracts every other body with a force that is
directly proportional to their masses and inversely proportional to the square
of the distance between their centers of mass. The greater the mass of the
object, the greater its gravitational force.


ELABORATE
Eccentricity Lab

Purpose:
To measure the eccentricity of different ellipses. Eccentricity is the ratio of
the distance between the foci to the length of the major axis.

Materials Needed:
Paper box, top lid 2 push pins string pencil
Paper metric ruler calculator

Procedure:
1. Tie a piece of string into a loop that fits on a piece of paper when laid out
as a circle.
2. Place the piece of paper on top of the box lid.
3. Stick the two push pins through the paper close to the center, but separated
from each other by a few centimeters.
4. Loop the string over the pins and use the pencil to trace around them,
keeping the string taut. (Hint: Make sure the push pins are lifted a little so
the string goes around the metal of the push pin, not the plastic top.)
5. Measure and record the major axis and the distance between the pin holes.
Calculate the eccentricity using the formula : Distance between foci
Length of major axis
(Hint: All answers should be between 0 and 1.)

6. Repeat steps 2 through 5 for other distances between foci and record results.

EVALUATE
Analysis:
1. What do the two pins represent in this experiment?
2. How does the eccentricity change as the distance between the pins changes?
3. What kind of figure would be formed if the two pins were at the same
location? What would its eccentricity be?
4. An ellipse closer to 1 would have what shape orbit?