Activities

Observing Projects

Observing tips and tools

If you do not have access to a telescope, you can learn a lot by observing the Moon through binoculars. Note that the Moon will appear right side up through binoculars but inverted through a telescope; if you are using a map of the Moon to aid your observations, you will need to take this into account. Inexpensive maps of the Moon can be purchased from most good bookstores or educational supply stores. You can determine the phase of the Moon either by looking at a calendar (most of which tell you the dates of new moon, first quarter, full moon, and third quarter), by checking the weather page of your newspaper, by consulting the current issue of Sky & Telescope or Astronomy magazine, by using the Starry Night program, or by using the World Wide Web.

  1. Observe the Moon through a telescope every few nights over a period of two weeks between new moon and full moon. Make sketches of various surface features, such as craters, mountain ranges, and maria. How does the appearance of these features change with the Moon’s phase? Which features are most easily seen at a low angle of illumination? Which features show up best with the Sun nearly overhead?

  2. Use Starry Night to examine the surface of the Moon. Select Favourites > Explorations > Luna. In order to see features on the surface of the Moon on the hemisphere facing away from the Sun, select Options > Solar System > Planets-Moons…from the menu. In the Planets-Moons Options dialog box, ensure that the Show dark side checkbox is checked and then slide the control for this option all the way to the right, to Brighter. This will artificially brighten the dark side of the Moon. Use the Zoom controls and location scroller to examine the surface of the Moon. (a) Based on your observations, what evidence can you find that the Moon is geologically inactive? Explain. (b) From your observations, explain the hypothesis that the darker gray lunar maria are geologically younger than the brighter highland regions of the Moon. (c) Spreading outward from some of the largest craters on the Moon are straight lines of slightly lighter-colored material, called rays, which were caused by material ejected outward by the impact that caused the crater. Use the Zoom controls and the location scroller to get a better view of these lunar features. Follow these rays across the lunar surface. Is there any evidence that this ejected material has disturbed crater walls during the violent impacts that caused these craters? Place the cursor over several of these impact craters and open the contextual menu (right-click on a PC, Ctrl-click on a Mac). The name of the crater will be found in the command “Mark crater name on surface.” (d) List at least three craters on the lunar surface that have rays.

  3. Use the Starry Night program to view the Moon as it appears from Earth and compare this with the view of Earth as it would appear from the Moon. Open the view named Favourites > Explorations > Moon From Earth. With the Time Flow Rate set at 1 day, Step time forward while observing the Moon in the view. Use the hand tool to adjust the screen as necessary to follow the Moon in the sky from day to day. When the Moon sets below the horizon, select File > Revert to return to the original view. Right-click (Ctrl-click on a Mac) over the image of the Moon and select Magnify from the contextual menu to center a magnified image of the Moon in the view. Next, type Ctrl-H (type B on a Mac) to remove the horizon from the view so that you may follow the appearance of the Moon over time without interference from the horizon. (a) Step time forward and observe the features on the Moon. Do you see a different view of the Moon from night to night or do you always see the same features on the Moon? Explain why the appearance of the Moon shows this behavior as time changes. Select Favourites > Discovering the Universe > Tranquility Base to change your viewing location to the Apollo 11 landing site on the Moon, with Earth visible in the lunar sky. With the Time Flow Rate at 1 hours, click the Play button in the toolbar. (b) Describe and explain your observations of the position of Earth in the lunar sky. Why does the lunar horizon not interfere with the visibility of Earth from this lunar viewing location?

  4. Use Starry Night to observe the apparent size of the Moon as seen from Earth. Select Favourites > Explorations > Moon Size. The view shows the full moon as it would appear from the north pole of Earth. Surrounding the Moon is a yellow circle that is precisely 30 arcminutes in diameter. As you can see, at the time and date of this view, the Moon does not quite fill this circle. To prevent the phases of the Moon from interfering with your observations of the size of the Moon in the sky, the dark hemisphere of the Moon is artificially brightened in this simulation. With the Time Flow Rate at 1 days, Step time forward and observe the size of the Moon relative to the 30′ reference circle. (a) Does the apparent size of the Moon remain constant? If not, explain what this tells us about the shape of the Moon’s orbit around Earth. (b) Approximately how many days does it take for the Moon to go through a complete cycle of variation of its apparent size? [Hint: Count the number of one-day time steps between two successive occasions when the Moon appears to fit precisely inside the 30′ reference circle. (c) As you make your observations, do the lunar surface features appear to remain stationary in the view? (They would remain stationary if the Moon’s synchronous rotation were the only motion that the Moon had relative to Earth.) If not, explain. (Hint: A Web search on the word “libration” [not libation!] may help.)

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Collaborative Exercise

  1. The image of Crater Clavius in Figure 10-4 reveals numerous craters. Using the idea that the Moon’s landscape can only be changed by impacts, make a rough sketch showing 10 of the largest craters and label them from oldest (those that showed up first) to youngest (the most recent ones). Explain your reasoning and any uncertainties.