Lab 9: The Moon, Revisited
You and your classmates have been observing the Moon over the past several weeks and have recorded some of these observations in detail. In this lab, we will assemble and interpret these observations to learn more about the many interesting phenomena associated with the Moon.
Part I: Interpreting our Observations of the Moon
Start by pulling out your own observations of the Moon and answer the following questions. If youre working with a small group or a partner, include their observations in questions 1-4.
1. What lunar phases did you succeed in observing? (list them all)
2. What was the range of lunar altitudes you (or your group partners) recorded? Was the Moon ever at the zenith?
3. Were you able to estimate the direction to the Moon? In what range of directions did you (or your lab partners) see the Moon?
4. Did you find that you could cover the Moon with the tip of your finger? Did the result depend on what phase the Moon was in, or how high in the sky it was?
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Now lets take a look at the full set of observations collected by the class. You can find all of your classmates observations on the iLearn Moon Observations forum. In the left column of the table name all of the lunar phases in order starting with New Moon. In the second column state the range of dates that you and your classmates observed that moon phase. If there was more than one range of dates for a given phase, include both!
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Sidereal vs Synodic Month
As the Earth goes around the Sun and as the Moon goes around the Earth, there are two different Moon cycles that we call a Sidereal Month and a Synodic Month. A sidereal month is the amount of time the Moon takes to complete one full revolution around the Earth with respect to the background stars, or in other words, for it to go 360? around its orbit. A sidereal month is about 27.3 days
A synodic month is the time it takes for the Moon to go back to the same phase. Because the Earth is going around the Sun, the same phase doesnt happen until it goes more than one full revolution around the Earth. The diagram below shows the difference between the Moons position after a sidereal month and synodic month as the Earth goes around the Sun. You can see that it takes a little bit of extra time for the Moon to go further around its orbit to reach another Full Moon.
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5. Sketch in a circle to represent the moon at locations corresponding to each of the four principal phases and label them. (Principal phases are those that occur on a single day in a lunar cycle!). Then work with the other members of your lab group to make your best estimate of the date on which each of these phases occurred. Write the dates next to the corresponding positions in orbit. If the observations cover more than one lunar cycle, some phases may be labeled with two dates.
6. Now, from your sketch above, make an estimate of the Moons synodic period (i.e., the number of days it takes for the cycle of phases to repeat itself). There is more than one way to do this! Explain in words how you made your estimate.
7. A synodic month is 29.5 days. How accurate was your estimate of the synodic period? Justify your answer.
