Observing Projects
Like Mars, Jupiter and Saturn are most easily seen around opposition. (The dates of Jupiter’s and Saturn’s oppositions are available on the World Wide Web.) Each planet is visible in the night sky for several months before or after its opposition. At other times, Jupiter and Saturn may be visible in either the predawn morning sky or the early evening sky. Consult such magazines as Sky & Telescope and Astronomy or their Web sites for more detailed information about when and where to look for Jupiter during a given month. You can also use the Starry Night™ program on the CD-ROM that accompanies selected copies of this textbook. A relatively small telescope with an objective diameter of 15 to 20 cm (6 to 8 inches), used with a medium-power eyepiece to give a magnification of 25× or so, should enable you to see some of the dark belts on Jupiter and the rings of Saturn.
If Jupiter is visible in the night sky, make arrangements to view the planet through a telescope. What magnifying power seems to give you the best view? Draw a picture of what you see. Can you see any belts and zones? How many? Can you see the Great Red Spot?
Make arrangements to view Jupiter’s Great Red Spot through a telescope. Consult the Sky & Telescope Web site, which lists the times when the center of the Great Red Spot passes across Jupiter’s central meridian. The Great Red Spot is well placed for viewing for 50 minutes before and after this happens. You will need a refractor with an objective of at least 15 cm (6 in.) diameter or a reflector with an objective of at least 20 cm (8 in.) diameter. Using a pale blue or green filter can increase the color contrast and make the spot more visible. For other useful hints, see the article “Tracking Jupiter’s Great Red Spot” by Alan MacRobert (Sky & Telescope, September 1997).
View Saturn through a small telescope. Make a sketch of what you see. Estimate the angle at which the rings are tilted to your line of sight. Can you see the Cassini division? Can you see any belts or zones in Saturn’s clouds? Is there a faint, starlike object near Saturn that might be Saturn’s satellite Titan? What observations could you perform to test whether the starlike object is a Saturnian satellite?
Use Starry Night™ to observe the appearance of Jupiter. Open Favourites > Explorations > Jupiter and use the Time Flow controls to determine the rotation period of the planet. (Hint: You may want to track the motion of an easily recognizable feature, such as the Great Red Spot.) (a) What is the approximate rotation period of Jupiter? (b) Measure Jupiter’s equatorial radius and its polar radius. You can use the angular separation tool to make these measurements. (Hint: Click on the cursor selection tool at the left side of the toolbar and select the angular measurement tool from the dropdown menu.) Measure from the center of the planet to its east or west limb (edge) along the equator of the planet to determine its equatorial radius and then measure from the center of the planet to its north or south pole to measure the polar radius. Are these two radii the same? If not, which is larger? Offer an explanation for this observation.
Use Starry Night™ to examine Jupiter. Open Favourites > Explorations > Jupiter. Select Options > Solar System > Planets-Moons…from the menu. In the Planets-Moons Options dialog window, click the checkbox for Surface guides and click OK to remove the pole sticks and equator from the image. Click the Stop button and then use the Zoom controls and location scroller to examine Jupiter’s atmosphere. (a) Describe the appearance of the atmosphere of the planet. (b) Compare the number of white ovals and brown ovals in Jupiter’s southern hemisphere (the hemisphere in which the Great Red Spot is located) with the number of white ovals and brown ovals visible in the northern hemisphere. What general rule can you state about the abundance of these storms in the two hemispheres.
Use Starry Night™ to observe the changing appearance of Saturn as seen from Earth. Select Favourites > Explorations > Atlas from the menu and click the Now button in the toolbar. Use the Find pane to locate and lock the view on Saturn (double-click the entry for Saturn). Zoom in until Saturn and its rings are clearly visible. Set the Time Flow Rate to 1 year. Now use the single-step forward button to observe the changing orientation of the rings as time advances in 1-year steps. (a) Describe qualitatively how the rings change orientation, as seen from Earth. (b) Use the Time controls to determine approximately how long it takes for Saturn’s rings, as seen from Earth, to go through a complete cycle from edge-on to fully open to edge-on to fully open and then finally to edge-on again. (c) Click the Now button to return to the present time. Use the Time controls to find during which of the next 30 years Saturn’s rings will appear edge-on as seen from Earth. (d) Why do we see the orientation of Saturn’s rings change in the way that you found in part (b)?
Use Starry Night™ to examine the rings of Saturn. Open Favourites > Explorations > Saturn and use the location scroller to view Saturn so that you are looking straight down on the plane of the rings. (a) Draw a copy of what you see and label the different rings and divisions. (b) Using the location scroller, adjust the view so that Saturn’s rings appear edge-on and then rotate the image until the Sun comes into view. Which of the following is correct?
Collaborative Exercise
Using a ruler with millimeter markings on five various images of Jupiter in the text, Figures 12-1a, 12-2a, and 12-4, determine the ratio of the longest width of the Great Red Spot to the full diameter of Jupiter. Each group member should measure a different image and all values should be averaged.
The text provides different years that spacecraft have flown by Jupiter and Saturn. List these dates and create a time line by listing one important event that was occurring on Earth during each of those years.
If the largest circle you can draw on a piece of paper represents the largest diameter of Saturn’s rings, about how large would Saturn be if scaled appropriately? Which item in a group member’s backpack is closest to this size?