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Purpose: To give the student experience with lunar phase observations.
Apparatus and Materials: Pencil, paper, calendar, and watch.
Introduction: The moon is the second brightest object in the sky and its appearance changes from night to night. The moon revolves around the Earth with a period of approximately 27.3 days (sidereal month). Due to the Earth’s orbital motion around the Sun, the synodic month that is observable from Earth is about 29.5 days. At any given time one half of the Moon is illuminated by the Sun. However, the fraction of the illuminated half that is actually visible from Earth depends on the positions of the Earth, Moon, and Sun. Hence, an observer on Earth sees the illuminated surface of the Moon change over time. In addition, since the Moon is in synchronous orbit around the Earth, it always presents the same face to the Earth.
The student should read Section 17.2 of the textbook prior to starting this experiment.
This experiment is a long-term (4 – 6 weeks) observational exercise that will familiarize the student with the various phases of the Moon. Because of its importance, this experiment is worth the equivalent of four labs (40 points).
1. Complete Table 1 prior to starting Step 2.
2. Choose a single convenient location from which to make all observations. You also need to determine due north and due south at your observation location. The observation location should also be relatively dark (i.e. away from streetlights), with most of the sky and horizon visible. Open fields and parking lots typically make good observation points.
3. Over a period of 4 – 6 weeks, observe and record the appearance (both a picture and description) and position of the Moon. In addition, record the date and time of each observation. Note that you will not be able to make all of your observations at the same time each night or day. Use Table 1 as a guide to adjust your viewing times. Record all data in a personal observation log.
Questions and Discussion:
1. Why is the same side of the Moon always visible from Earth?
2. During what phase of the Moon can a solar eclipse occur?
3. Using a drawing, show the relative positions of the Sun, Earth and Moon during a total solar eclipse. Indicate the locations of the shadows from both the Earth and the Moon.
1. An Introduction to Physical Science Laboratory Guide, 10th Edition, James T. Shipman and Clyde D. Baker, “Observing the Phases of the Moon”, Experiment 43, Houghton Mifflin Company (2003).
2. An Introduction to Physical Science, 11th Edition, James T. Shipman, Jerry D. Wilson, and Aaron W. Todd, Houghton Mifflin Company (2006).
3. Astronomy: A Beginner’s Guide to the Universe, 5th Edition, Eric Chaisson and Steve McMillan, Pearson Education Inc., (2007).