Name _______________________________________________ Date ______ Per _____
Retrograde Motion Web Tool Lab
Purpose: To demonstrate the cause of apparent retrograde motion.
Data:
Earth
Radius of Orbit
Period of revolution (Earth Days)
Circumference of orbits
150,000,000 Km
365 days
942,000,000 Km
Mars
228,000,000 Km
687 days
1,431,000,000 Km
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 window labeled Earth’s Sky. 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.
Right Click on the window to see Earth and Mars if they are not visible.
a. What color is used to represent each planet?
1. Earth ________________________
b.
2. Mars ________________________
What color circle represents Mars in Earth's nighttime sky? __________
2. Starting with the first time you see Mars in Earth's sky as #1 Click on the diagram
and count how many times Mars moves toward the east. Note Mars will change
color on the diagram when Eastward progression through Earth's sky stops.
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.