Name Date Score /20 Phases of the Moon Objective Working with models for the Earth-Moon-Sun system, the student will simulate the phases the Moon passes through each month. Upon completion of this exercise, the student will be able to model the cycle of Moon phases as seen from the Earth identify the progression of the phases from a series of images distinguish the dark side of the Moon from the far side of the Moon relate the location of the Moon in the sky to its phase state the continuity of the Moon phases world wide disprove a common misconception about why the Moon goes through phases relate images of the Moon to the Moon s location in its orbit concisely evaluate and summarize his/her learning Materials Special chart paper located on the last page of this exercise Bright light source (100 W light bulb, large flashlight) to represent the Sun Medium-sized white ball (softball, baseball, Styrofoam ball of similar size) for the Moon Basketball (or similarly sized ball -- roughly 4 times the size of the Moon) to represent the Earth. Procedure One important comment before we start: The fact that the Moon always keeps the same side facing the Earth is not relevant for why the Moon goes through its phases. We would see the Moon go through phases even if it were a perfectly smooth, uniform ball (like a cue ball). For the "Hands-on" part of this exercise, we are going to work from two points of view. First, your head will be the Earth and you will hold the Moon at arms length while going through a complete cycle of phases. Second, we bring in the basketball and softball (or any two objects you have around that will work) so that we can duplicate the privileged view, high above the north pole of the Earth, and go through a complete cycle of phases. Introduction: Sitting on Earth (or, your head as the world) Use a bright light source (such as a 100 watt+ light bulb, no lamp shade) to represent the Sun. If you are using a Styrofoam ball, then you may wish to skewer it so that you may hold your Moon up away from your hand. Your head represents the planet Earth. Since the Earth rotates counterclockwise from a northern-hemisphere bias, your left ear will be "East" and your right ear, "West." You will rotate towards the East. a. With the Moon held at arm's length, rotate your body as if you were the Earth through one complete day (rotating left or counterclockwise). In actuality, your Earth-head would need to rotate about 30 times during one Moon orbit. (Unfortunately, we don t know how to do this realistically yet.) Hold the Moon up a bit above your head so as not to have any eclipses of the Moon or Sun. The real Moon s orbit is tilted with respect to the Earth-Sun plane, and so eclipses do not happen every month. 4/7/10 phases_moon.doc 1
b. Holding your body still, put the Moon through one complete orbit, circling your head counterclockwise without moving your head. Your eyes will need to roll around to see the Moon, however. c. Now face the Sun so that it is noon where you live let s say you live on the tip of your nose. Hold the Moon in between you and the Sun. You are looking at the dark side of the Moon. What phase is the Moon in? Where is the far side of the Moon, the side that always faces away from the Earth? d. Now take the Moon through one complete month by holding it out at arm s length and moving it and your body counterclockwise 360 degrees. e. Do the same procedure, but this time starting with a full Moon. (You will need to figure out the alignment for the Sun and Earth and Moon. HINT: it is midnight on your nose.) Where is the dark side of the Moon now? Where is the far side of the Moon? f. What time is it where you are if you see a full Moon high up in the middle of the southern sky (assuming you live in the northern hemisphere)? g. Position yourself and the Moon so that the Moon is in its 1st quarter phase (See Fig. 1.B in Part II). Mentally note the Sun-Earth-Moon positions. Where is the dark side of the Moon? Where is the far side of the Moon? h. Position yourself and the Moon so that the Moon is in its 3rd quarter phase (See Fig. 1.H in Part II). Mentally note the Sun-Earth-Moon positions. How is the alignment different from that when the Moon is in its 1st quarter phase? Where is the dark side of the Moon? Where is the far side of the Moon? PART I 1. (1 pts) In Step C, what phase was the Moon in? The dark side was facing you (the side that was in the shadow no sunlight hitting it). Where was the far side of the Moon? 2. (1 pts) In Step E, you had a full Moon. Where was the dark side of the Moon? Where was the far side of the Moon? 3. (1 pts) When the Moon is in its first-quarter phase, can we see the far side of the Moon? How much of the dark side of the Moon are we able to see? 4. (1 pts) Explain what we mean when we talk about the "far side of the Moon" and how it differs from the "dark side of the Moon." 2
PART II -- ORDERING THE PHASES A B C D E F G H I Figure 1. Moon phases seen in random order. Starting with "J" (a new moon), put the phases in order, from new moon to full moon to new moon again (see question 5 that follows). K J 5. (2 pts) The images for this part are seen in Figure 1. Starting with "J" (a new moon), put the phases in order, from new moon to full moon to new moon again. A good way to do this might be to cut out the squares and arrange on a flat surface. J J 3
PART III -- A Privileged View of the Earth Moon System Now, we are going to assume that it takes the Moon 30 days to orbit the Earth once and realign itself with respect to the Sun, rather than the 29.5 days. This makes 360 degrees divided by 30 days and means the Moon moves approximately 12 degrees in its orbit for every Earth day, and our modeling becomes easier. Use the special chart on the last page of this exercise to guide you (or one handed out in class). It will help you place the Moon along in its orbit according to how many degrees it has moved. Place your "Earth" in the center of the chart paper. It doesn t matter if it takes up a lot of room, the chart is just a guide. For this part you will be using the "basketball Earth" and "softball" Moon (or whatever you have on hand). Now, for each rotation of the Earth (1 day) the Moon would move along in its orbit by 12 degrees. It's hard to make this completely realistic, mostly because we will get an eclipse of the Sun or Moon every time. To do this entirely to scale, with a basketball Earth and a Moon approximately a 10-cm baseball, the Earth-Moon distance would be 10 meters (about 11 yards), and the Earth-Sun distance 4 kilometers away (2.5 miles!) 6. (1 pt) Starting with a new moon (Sun-Moon-Earth alignment), rotate the Earth once, without moving the Moon. If we could, in fact, "see" a new moon, over the 24 hours, would all locations on the Earth see a new moon, or close to a new moon? [IGNORE the North and South Pole regions.] Answer: yes no 7. (1 pt) Move the Moon along in its orbit until it is in its first-quarter phase (it orbits counterclockwise); this will be 90 degrees. Since this is about 1/4 of a month, the Earth will have rotated about one-fourth of 30 days, or 7.5 times. Leave the Moon in this position and rotate the Earth. Do all locations on Earth see a 1st quarter moon, or close to it over the course of 1 day on Earth? Answer: yes no 8. (1 pt) Move the Moon until the alignment is Sun-Earth-Moon. What is the phase of the Moon? Rotate the Earth through 1 day, leaving the Moon fixed. Do all locations on Earth see the same phase (or close to it) during one day on the Earth? Answer: yes no The key to getting the above questions correct is visualizing how much the phase of the Moon actually changes over a 24 hour period: about 12 degrees. How much of a difference will that make? Shown at the right is the very common image of the Moon phases that leads to the misconception of what people in different parts of the world see over a given 24-hour day. Figure 2. 4
PART IV-- Analytical Questions 9. (1 pt) It is sunset on some random day of the month. Face south. In what direction is the Sun? You see the Moon on the meridian. What phase is the Moon in? new 1 st quarter waxing gibbous full 3 rd quarter waning crescent 10. (1 pt) It is sunrise on another random day of the month (about 2 weeks from the day in question 2). Face south. In what direction is the Sun? You see the Moon on the meridian. What phase is the Moon in? new 1 st quarter waxing gibbous full 3 rd quarter waning crescent 11. (1 pt) Which of the following could never happen? a. An observer seeing a full moon in the middle of the day at his or her noon time. b. An observer seeing a new moon in the middle of the night at his or her midnight. c. Both of the above observations are impossible for any observer to see. 12. (1 pt) If you see a full moon in the sky at around midnight where you live, what phase of the Moon does someone who lives on the opposite side of the Earth see at around midnight where they live? [HINT: Be sure to be consistent with your answers given above.] new 1 st quarter waxing gibbous full 3 rd quarter waning crescent 13. (2 pts) One of the common misconceptions about the Moon going through phases is that they occur because the Moon passes through the Earth s shadow during each month. For science, it is sufficient to note just one observation that negates this "shadowed Moon" theory to have the theory thrown out as invalid. The image here, Fig. 3, was taken looking almost due west from Seattle at 9:20 pm, PDT. Think about what phase the Moon is in, where the Earth s shadow points, and then explain why the Earth s shadow cannot be the reason for the Moon going through its phases, using this example to correct that misconception. (The double-peaked mountain is the Brothers; Venus is also in the west.) Figure 3. 5
14. (1 pt ) Approximately, in what position was the Moon located in its orbit when the image seen in Fig. 3 was taken? (If you get the correct position, you can also draw in the shadows of the Earth and Moon to support your answer for question 13.) 1 2 3 4 5 6 7 8 15. (4 pts) In a well-written paragraph, compare what you knew about the phases of the Moon prior to this exercise and how that knowledge changed upon completing this assignment. Summarize the concepts that were the most difficult to understand as well as those that seemed relatively easy. 6