Name ______Date______
Adapted from Marrazo
In-Class Lab Ellipses
Background:
The earth revolves around the sun in an orbit which is a special geometricfigure called an ellipse. An ellipse has two "center points". Each one is called a foci. The Sun is not in the exact middle of the earth's orbit. The Sun is found at one of the focal points. The degree of flatness or “ovalness” of an ellipse is measured by eccentricity.
OBJECTIVE: You will construct and measure and interpret various ellipses and compare them to planets found within our Solar System.
The eccentricity of an ellipse tells us how "out of round" it is. The formula can be found on page 1 of your Earth Science Reference Tables
PROCEDURE:
1.Gather all the materials you need to complete this lab (See Fig. 1):
- A piece of cardboard
- 2 push pins
- A string loop
- Ruler
- ESRT
- A sharp pencil
5. Now, measure the distance between the straight pin holes (foci). This is "d". Record this on your Report Sheet. (Last page)
6. Measure the length of the major axis (L) and record this on the Report Sheet.
7. Calculate the eccentricity of this loop and record this on the Report Sheet.
Report Sheet
Express all answers to the nearest thousandths .000
Ellipse #1Calculations
d = ______
L = ______
e = ______
Ellipse #2Calculations
d = ______
L = ______
e = ______
Ellipse #3
Calculations
d = ______
L = ______
e = ______
1.On ellipse #3 that you drew, label one of the foci with the letter S for Sun. Now, place the letter A on the elliptical path where the planet would be moving the fastest in its orbit around the sun.
2.What changes do you see in the eccentricity (e) of your ellipses as you INCREASE the distance between the foci (pins).
3.Out of the 3 ellipses you drew, which has the most eccentric? ______
4.Out of the 3 ellipses you drew, which is the least eccentric? ______
5.Which is less eccentric, the orbit of the Earth or Ellipse #1? ______
6.Which planet in our solar system has the most eccentric orbit? ______
7.Describe the true shape of the Earths orbit.
8.How does the numerical value of "e" change as the ellipse approaches a straight line?
Regents Questions:
Questions 1 through 5 refer to the following: The diagram below represents planet Z in its orbit
around star A. Locations 1 through 4 of planet Z are indicated on the orbit. The sizes of the planet and the star are not drawn to scale. The elliptical orbit of planet Z and the distance between the foci (F1 and F2) are drawn to scale.
_____1) Star A would have the greatest apparent size to an observer on planet Z when the planet is at location
A) 1
B) 2
C) 3
D) 4
_____2) What is the approximate eccentricity of the elliptical orbit of planet Z?
A) 1
B) 0.2
C) 0.7
D) 0.1
_____3) As planet Z travels around star A in a complete orbit starting from location 1, the orbital
velocity of the planet will
A) decrease, then increase
B) increase, then decrease
C) continually increase
D) remain the same
_____4) The orbiting motion of planet Z around star A isknown as
A) rotation
B) inclination
C) revolution
D) declination
_____5) At which location would the gravitational force between star A and planet Z be least?
A) 1C) 3
B) 2D) 4