Retrograde Motion
Introduction
The figure below is a very basic depiction of the orbits of Venus, Earth, and Mars.
1) Which of the three planets shown takes the
least amount of time to orbit the Sun?
2) Which of the three planets shown has the largest orbit?
3) Would Mars be visible from Earth as shown in the picture? Why or why not?
4) Would Venus be visible from Earth as shown in the picture? Why or why not?
5) Indicate on the picture the range of positions in Mars’ orbit for when it will be visible from Earth.
6) Indicate on the picture the range of positions in Venus’ orbit for when it will be visible from Earth.
Background
The table on the next page provides positions of Mars over one year. The table also includes the positions of various background stars to serve as a reference, and selected points to help locate the path of the Sun, also known as the ecliptic.
Right Ascension is the equivalent of longitude on the celestial sphere, whereas Declination is the equivalent of latitude. The RA coordinate system allows astronomers to agree on the relative positions of celestial objects without the concern of where on Earth the objects are being observed from.
Procedure
· Plot the background stars on the graph provided on the next page.
· Plot the selected points on the ecliptic, making sure to use a different color than what was used for the background stars.
o Connect the points of the ecliptic to show the Sun’s path
· Plot the locations of Mars using the coordinates provided
o Connect the points of Mars, making sure to do so in chronological order.
Questions
1) Compare the overall location of the ecliptic to the path of Mars.
2) What do you notice about the path of Mars over the course of the year provided?
3) Would Venus exhibit this strange behavior? Why or why not?
4) Would Jupiter exhibit this strange behavior? Why or why not?
5) Create a hypothesis for why the path of Mars is unusual.