Name _______________________________ Date ______________

Construct Planetary Orbits Around the Sun
Student Activity Sheet

Source: Glencoe Division of Macmillan/McGraw-Hill

Materials:

thumbtacks or pins, string, cardboard (21.5 cm x 28 cm), metric ruler, pencil, paper, calculator.

Purpose:

In this activity student will learn how to make an ellipse using string and how varying the length of the string alters the shape of the ellipse. Students will also learn how characteristics of an ellipse relate to the orbits of the planets.

Procedure:

Part A

  1. Place a blank sheet of paper on top of the cardboard and place two thumbtacks or pins about 3 cm apart.
  2. Tie the string into a circle with a circumference of 15 to 20 cm. Loop the string around the thumbtacks. With someone holding the tacks or pins, place a pencil inside the loop and pull it taut.
  3. Move the pen or pencil around the tacks, keeping the string taut, until you have completed a smooth, closed curve or an ellipse.
  4. Repeat Steps 1 though 3 several times. First vary the distance between the tacks and then vary the circumference of the string. However, change only one of these each time. Note the effect on the size and shape of the ellipse with each of these changes.
  5. Orbits are usually described in terms of eccentricity (e) The eccentricity of any ellipse is determined by dividing the distance ( d ) between the foci or tacks by the length of the major axis (L). Measure and record (d) and (L) for each ellipse you created.
  6. Calculate and record the eccentricity of the ellipses that you constructed.

Part B

  1. Refer to the chart of eccentricities of planetary orbits to construct an ellipse with the same eccentricity as Earth's orbit.
  2. Repeat Step 1 with the orbit of Pluto and Mercury.
PlanetEccentricity
Mercury 0.21
Venus 0.01
Earth 0.02
Mars 0.09
Jupiter 0.05
Saturn 0.06
Uranus 0.05
Neptune 0.01
Pluto 0.25

Data and Observations

Record Information from Part A:

Constructed
ellipse		 d
(cm)		 L
(cm)		 e
(d/L)
#1
#2
#3
Earth's orbit
Mercury's orbit
Pluto's orbit

Analyze:

  1. What effect does a change in the length of the string or the distance between the tacks have on the shape of the ellipse?

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  2. What must be done to the string or placement of tacks to decrease the eccentricity of the constructed ellipse?

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Conclude and Apply

  1. Describe the shape of Earth's orbit. Where is the Sun located within the orbit?

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  2. Name the planets that have the most eccentric orbits.

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  3. Using Kepler's third law and the (L) from your chart for Earth, Mercury, and Pluto, calculate the period of revolution for these three planets.

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[LMGFP home page] Contact Karen Krupinsky (kgurley@gsfc.nasa.gov) or
Tammy Seergae (tseergae@umd.edu) for further information.