Purpose: To demonstrate the cause of apparent retrograde motion.

Hypothesis: The Earth overtaking and passing a planet as the two revolve around the sun in different orbits causes the apparent retrograde motion of a planet.

Part 1.

1. Calculate the distance Earth and Mars each travels along it's orbit for one Earth day.

Earth _____________________ Mars ___________________

2. Do the planets travel at the same speed? _________________

3. If not, which planet is moving faster? ____________________

Part 2.

1. Take a look at the diagram below. (Hit refresh on the  browser if the image is not clear)

Above the yellow line represents an area in Earth's nighttime sky (minus the stars). Below the yellow line represents a view of outer space above the revolving planets of Earth & Mars. If both planets are not visible, right click on the diagram to see Earth and Mars.

           a. What color is used to represent each planet?

                1. Earth ________________________

                2. Mars ________________________

           b. What color circle represents Mars in Earth's nighttime sky? ______________

           a. At what number circle did Mars change color showing Eastward progression through
               the nighttime sky had stopped? _______________

           b. What direction did Mars appear to go across the nighttime sky after it changed color?
                 __________________

           c. Continue clicking and counting. How many clicks does Mars appear to go in this
               opposite direction?_______

If you make a mistake in counting just hit the refresh button on the browser and start again.

           d. What is this opposite motion known as? ________________________

           e.   What # click does Mars return to its original direction of motion across Earth's
                 nighttime sky? __________

3. Click through the sequence a few times and pay attention to the distance mars travel after each click.

           a. Did the distance Mars appeared to travel across Earth's nighttime sky change between
              clicks?___________

           b. Looking at the space view, is there any change in the distance it actually traveled?
               ____________________

           c. In the nighttime view (Earth's Sky), what has happened to the apparent speed of Mars?
                __________________________ 

4. It take approximately 10.7 days for Earth to move form one point to the next in its orbit as shown in the diagram. Based on this, how long did the apparent retrograde motion of Mars last for this example? _______________ days

5 Explain in detail how this diagram supports the hypothesis at the beginning of this lab.

6. Using what you know of Apparent Retrograde Motion write down any similar situations occurring in everyday life.