You should have completed the slide show (previous exercise) before starting this discussion.

Most of the "questions" below will be steps to be followed, but some questions require answers to by typed in the appropriate blancks or multiple choice selections.

You need a planisphere.
You need a copy of the negative print from the previous page.
You should also have the slide show created in the previous exercise.

Your name and score will be sent automatically to your instructor whenever you enter this exercise. Feel free to enter as many times as you wish in order to feel comfortable with the material. If you wish more help, feel free to e-mail the instructor.

1. Run the slide show that you created in the previous page.
   Pause at one of the images and note the date. What month (abbrev) did the particular image occur?
   

   
   
   CheckHintShow answer

2. A. Set the planisphere for the date and time of the image (assume that the image was photographed at 9:00 PM).
   B. Locate the constellation(s) or stars which show up in each image of the slide show.
   C. Assume that each image was made at 9:00 pm on its date. Set the planisphere for each date for each successive image of the slideshow.
   D. How does the constellation in the neighborhood of the planet appear in the sky for each successive month at 9:00 pm?

   1.   ?    The constellation of the planet starts in the low east in the early months and gradually appears further to the celestial west.
   2.   ?    The constellation is in the same part of the sky in each successive month.
   3.   ?    The constellation of the planet starts in the western part of the sky in the early months and migrates further east.
   4.   ?    The constellation location is purely random with no sense of order from one month to the next.

3. What is the best explanation of the reason the constellation containing the planet is in a different part of the sky for each image?

   1.   ?    The earth is in orbit around the sun. As the months progress, the side of the celestial sphere on the night side of the earth is different.
   2.   ?    As the months progress, the sky rotates around the earth at a different rate from the sun.
   3.   ?    The constellations wander to random parts of the sky.
   4.   ?    The constellations migrate from the northern horizon to the southern horizon.
   5.   ?    The constellations migrate from the southern horizon to the northern horizon.

4. A. The camera was mounted on a tripod and looked up at the sky to make each image. Because the sky appears to rotate about the north celestial pole, the orientation of the stars in each image is different as the weeks and months progress. To examine the smooth motion of the planet on the field of stars, each image has been rotated and oriented so that the stars and asterisms appear at the same orientation on each image. This required a lot of work by the instructor using AIP4WINDOWS by Richard Berry.
   
   B. On your negative print, mark with an arrow the direction of celestial north. This is rather tricky! Consult the planisphere. Orient the negative print of the field stars over the planisphere so that the orientation of the constellations and asterisms match. The tricky part of this is the fact that the scale of the planisphere is different from that of the photograph, and you cannot see through the paper very well. Celestial north is the direction in the star fields toward the north celestial pole.
   
   C. On your negative print, mark with another arrow the direction of celestial east. That is 90 deg to the left of celestial north. Notice that east is opposite to a land compass reading because we are looking up from underneath at a map of the stars. There is no way to check this answer on the computer. It is best that you e-mail your instructor a precise description of your North and East directions. See the Jupiter, 2004 image as an example.
   
   Main question: The planets all orbit the sun toward celestial east. All the planets' orbits lie within a few degrees of the ecliptic plane. Which direction do you expect the planets to appear to move as the planets and the earth are orbiting the sun towards celestial east?
   

   1.   ?    East
   2.   ?    North
   3.   ?    South
   4.   ?    West

5. Examine the animated slideshow that you produced in the previous lesson (you should have created a file on your hard drive or server drive). Also consult your planisphere. Find the month at which the constellation where the planet is located is halfway between the east and west horizon at 9:00 pm.. This is the month of the 9:00 pm meridian crossing.
   
   Restrict the slideshow to the months prior to the month of the 9:00 pm meridian crossing. In what direction relative to the stars does the planet appear to move for these months before meridian crossing?
   

   1.   ?    West
   2.   ?    East
   3.   ?    North
   4.   ?    South

6. Compare your prediction of question 4 with the correct answer for Question 5.

   1.   ?    I was correct in my prediction
   2.   ?    I was incorrect in my prediction. I predicted the planet would appear to move in the same direction that it actually moved.
   3.   ?    I was way-off in my prediction - choosing North or South apparent motion.

7. Examine the applets that others have published:
   McGraw Hill
   UIUC
   
   Which answer best explains the retrograde motion of the planets?

   1.   ?    The planet orbits with a circle on a circle - or epicycle.
   2.   ?    The earth orbits the sun faster than the outer planet, thus passing the planet like a car on the inner lane of a race track passing the cars on the outer lanes. The cars in the outer lanes appear to the driver to be drifting backwards.
   3.   ?    The planet actually stops and goes backwards for awhile, then resumes its forward motion again.
   4.   ?    The outer planet orbits the sun at the same speed (one year to complete an orbit). This causes the planet's position among the stars to appear to move backwards.

8. In the time of year when the earth-sun-outer planet angle is 90 degrees, see diagram, what is the apparent motion of the outer planet?
   

   1.   ?    The planet appears stationary and is changing direction from retrograde to prograde.
   2.   ?    The planet is moving in retrograde (backwards) motion toward the celestial west.
   3.   ?    The planet is moving in retrograde (backwards) motion toward the celestial west, but at a slower rate.
   4.   ?    The planet appears to move eastward (prograde).

9. Suppose you were located on Jupiter or in a spacecraft orbiting Jupiter and watched the earth and the sun when the Jupiter-sun-earth angle were 90 degrees (see the same diagram as the previous question). Which answer best describes the relative motion of the earth seen from this point? Note: this is analogous to the apparent motion of Venus as seen from earth.

   1.   ?    The earth appears to the west of the sun (as seen from Jupiter), and it maintains the same distance from the sun throughout this period.
   2.   ?    The earth appears to the west of the sun (as seen from Jupiter), and it becomes further and further west of the sun.
   3.   ?    The earth appears to the west of the sun (as seen from Jupiter), and it becomes closer and closer to the sun.
   4.   ?    The earth passes between Jupiter and the sun and is not visible from Jupiter.

10. Consider the time when Jupiter is at opposition relative to the earth as in the (linked diagram of opposition). Which answer best describes the apparent motion of Jupiter relative to the background stars during this period.

    1.   ?    Jupiter is moving west relative to the stars (retrograde motion)
    2.   ?    Jupiter is moving east relative to the stars. Note the absolute motion toward the east for both earth and Jupiter.
    3.   ?    Jupiter is stationary relative to the stars - i. e. it is changing between prograde and retrograde motion.
    4.   ?    Jupiter is not visible because of the sun's glare.