Name ______Block ___
Retrograde Motion
One of the most difficult parts of constructing an accurate model for planetary motions is that the planets seem to wander among the stars. During their normal (or prograde) motion, planets appear to move from west to east over many consecutive nights as seen against the background of stars. However, they occasionally, and predictably, appear to reverse direction and move east to west over consecutive nights as seen against the background stars. This backwards motion is called retrograde motion.
1)Given the data in Table 1, plot the motion of the mystery planet on the graph provided in figure 1 (record dates next to each position that you plot). Then, draw a smooth line (or curve), using your data points, to illustrate the path of the planet through the sky.
Table 1: Mystery Planet Positions
Date of Observation / Azimuth (horizontal direction) / Altitude(vertical direction)May 1 / 240 / 45
May 5 / 210 / 50
June 1 / 170 / 50
June 15 / 150 / 45
July 1 / 170 / 40
July 15 / 180 / 45
August 1 / 140 / 50
August 15 / 120 / 55
The dots on this
graph are
background stars!
2. On what date, was the mystery planet located furthest to the west? What was the azimuth value of the planet on this date?
3. On what date was the mystery planet located furthest to the east. What was the azimuth value of the planet on this date?
4. Describe how the mystery planet moved (to the east or to the west), as compared to the background stars, during the time between the dates identified in questions 2 and 3.
5. During which dates does the mystery planet appear to move with normal(prograde) motion, as compared to the background stars?
6. In what direction, (east-to-west or west-to-east) does the planet appear to be moving relative to the background stars at this time?
7. During which dates does this mystery planet appear to move with a backward(retrograde) motion as compared to the background stars?
8. In what direction, east-to-west or west-to-east, does the planet appear to be moving relative to the background stars during this time?
9. Suppose your instructor says that Mars is moving with retrograde motion tonight and will rise at midnight. Consider the following student statement:
Student: Since Mars is moving with retrograde motion that means that during the night it will be moving west-to-east rather than east-to-west. So at midnight it will rise in the west and move across the sky and then set later in the east.
Do you agree or disagree with the student? Explain your reasoning.