The Rhythm of the Spheres

(Downloadable Student Handout - Copy and Paste)

Part 1: Engage

The Solar System is often compared to a clock. Every planet, moon, and asteroid stays in its own lane, moving at predictable speeds for billions of years without crashing into each other.

The Puzzling Question: Why does the Earth stay exactly 1 AU from the Sun? Why don’t we drift away into the cold of space, or get pulled into the Sun’s fire? What “invisible strings” are keeping the clock ticking?

Write your “Need to Know” questions:

Part 2: Explore

Open the Orbital Motion & Kepler’s Laws Simulation.

Investigation A: The Shape of an Orbit

  1. Select the Earth-Sun System.
  2. Change the Eccentricity slider from 0.0 to 0.7.
  3. Click Show Trajectory.
    • How does the shape of the path change as eccentricity increases?
    • Where is the Sun located in the new, oval-shaped orbit?
  4. Measure the distance from the Sun at its closest point (Perihelion) and farthest point (Aphelion).

Investigation B: Speed and Distance

  1. Return to a circular orbit (Eccentricity = 0).
  2. Click Show Velocity Vector.
  3. Now, move the Earth farther from the Sun. Look at the “Orbital Velocity” display.
    • Does the planet move FASTER or SLOWER when it is farther away?
  4. Switch to the Jupiter-Sun System. Compare Jupiter’s average orbital speed to Earth’s.

Part 3: Explain

  1. Analyze the Physics: What two forces must be in balance for a planet to maintain a stable, circular orbit? Use the simulation’s “Gravity Vector” and “Velocity Vector” displays to support your answer.
  2. Kepler’s Insights: Based on your observations in Investigation A, explain why planets move faster when they are closer to the Sun.
  3. Predicting Motion: If you suddenly doubled the mass of the Sun in the simulation, what would happen to Earth’s orbit? (Try it!) Explain why the orbit changed.

Part 4: Elaborate & Evaluate

The Mission Challenge: You are a NASA engineer designing a mission to Mars. Mars has a more eccentric orbit than Earth.

Construct a Scientific Prediction: Using Kepler’s Laws (which you visualized in the simulation), explain how the distance between Earth and Mars changes over time.

  1. Draw or describe a model of the two orbits.
  2. Predict the best “window” for a spacecraft to travel between them using the least amount of fuel.
  3. Explain how the Eccentricity of Mars’ orbit makes this prediction more difficult than if the orbits were perfect circles.

(Space for scientific prediction)