Name_________________________________Date___________________Period________
Retrograde Simulator Online Activity
To do the assignment, login into the following website……
http://wikifuller.wikispaces.com/
Click on the “Solar System e - Learning” link on the left side of page directly underneath the
“home” link. Scroll down the webpage until you have found the correct activity that matches the
assignment.
Before doing the online interactive, read the introduction below and answer the following
questions:
Introduction:
Planets look like stars in the night sky. So if planets look like stars, how do we
tell them apart? Well, for one thing, planets are much, much closer than the stars therefore they
move faster across the night sky. By tracking their motions across the night sky we will be able tell
planets apart from stars. In the night sky, planets move fast compared to the background stars
which for the most part remain stationary or “fixed”. On the other hand, planets readily move over
the course of a year. Planets generally move in a west to east fashion across the night sky. We
called this prograde motion. However, many planets reverse their direction and appear as if they
are going “backwards” for a brief period of time. We call this retrograde motion. This activity will
explain why planets appear to move “backwards” in the night sky
1. How do we tell the difference between stars and planets in the night sky?????
2. What is prograde motion of planets?????
3. What is retrograde motion of planets?????
4. Considering your answer to the previous questions, explain the difference between prograde and retrograde
planetary motion:
Before we begin, make sure you click on the “interactive” tab at the top.
Under view controls, make sure you are looking from EARTH and looking at MARS!
6. Analyze the orbits of Earth and Mars????? Which one orbits faster???? Which one orbits slower????
7. Which planet appears to be orbiting the sun the fastest???? Which planet appears to be orbiting the
sun the slowest????
8. Analyze the movement of mars compared to the background stars. Do the stars and the planet Mars
move at the same speed????
8. No click on the “show trace” box. As earth gets closer to mars and starts to pass it, what does the
path of mars appear to do in the night sky??????
9. Consider your answer to the previous question. Is this movement PROGRADE or RETROGRADE
motion of planets??????
10. As the two planets orbit and earth gets farther from Mars, does the path of Mars in the night sky
continue to demonstrate RETROGRADE motion, or does it change back to PROGRADE motion????? In
other words, does it appear to move backward or forward?????
11. Compare the movements of planets with far distant stars. Do stars show retrograde motion???
12. How do you think ancient astronomers were able to tell the difference between stars and
planets?????
Under view controls, now look from EARTH and look at VENUS!
13. Compare the orbit speeds of Venus and Earth, which one orbits faster???? Which one orbits
slower????
14. As venus orbits the sun and starts to come close to earth, does the path of Venus continue to
demonstrate RETROGRADE motion, or does it change back to PROGRADE motion????? In other
words, does it appear to move backward or forward?????
Quiz:
1. Planets are much closer to the earth than the stars. Evidence for this can be observed in the
_________motions of planets during the evening.
a.
b.
c.
d.
eccentric
elliptical
retrograde
constant
2. What happens during the apparent Retrograde motion of a planet?
a) the planet moves backward in its orbit around the sun
b) the planet appears to move north and south with respect to the stars over a period of many nights.
c) the planet is getting closer to the Sun in its orbit.
d) the planet rises in the west and sets in the east.
e) the planet moves through constellations that are not part of the zodiac
3. _______ motion is the apparent backwards movement of a planet compared to far off stars.
a. Retrograde
b. Parallax
c. Precession
d. Rotation