Astronomy Lab Lunar Phases.docx

Lunar Phase Simulator – Student Guide Part I: Background Material Answer the following questions after reviewing the background pages for the simulator. Page 1 – Introduction to Moon Phases Is there a dark side of the moon? (Note: this question can be effectively answered either yes or no, so it is important to explain your reasoning.) Yes; there is always a side of the moon that faces away from the Earth, making it known as the “dark side.” How long does it take the moon to complete one cycle of phases, in days? 29.5 Days If the moon is full today, what phase do you expect it to be at in a week? Third Quarter How about one month later? If the moon is full today, it will be a full moon again a month later. Many words in astronomy are also non-astronomical uses as well. Using your knowledge of how the terms on the left are used in astronomy match them with the non- astronomical uses on the right. waning convex, rounded -- also hunch-backed, having a hump gibbous to increase in size, quantity, volume, intensity, etc. waxing decrease in magnitude, importance, brilliancy, intensity, etc. The following sketches of the moon's appearance were made over about four weeks. Identify the phases and put them in the correct numerical order. One is labeled for you. NAAP – Lunar Phase Simulator 1/10

Picture Order Phase Picture Order Phase A 3 Waning Crescent D 4 First Quarter B 1 Waning Gibbous E 5 Waxing Gibbous C 6 Full Moon F 2 Third Quarter Page 2 – Introduction to Moon Phases From the perspective of an observer above the North Pole, the moon moves clockwise / counter-clockwise (circle) in its orbit around the earth. In the diagram below the sun's light is coming in from the right. The moon's location is marked at several points on its orbit. These are the points the moon was at when the sketches above were drawn. Identify each position with the letter of the corresponding sketch. NAAP – Lunar Phase Simulator 2/10 D

Page 3 – The Time of Day Use the interactive diagram at the bottom of the page to determine the direction of the earth’s rotation when viewed from above the North Pole. (Hint: rotate the observer – the stick figure – to the noontime position, then sunset position, then midnight position, and finally back to sunrise position. The earth has made one complete rotation and the observer has experience one daily (diurnal) cycle of day and night.) When viewed from above the North Pole, does the earth rotate clockwise or counter-clockwise? Counter-Clockwise Page 4 – Rising and Setting When the moon crosses the western side of the horizon plane it is rising / setting (circle). When it crosses the eastern side of the horizon plane it is rising / setting (circle). Page 5 – The Horizon Diagram NAAP – Lunar Phase Simulator 3/10 E A F B C

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Moon Earth sunlight Describe the location of the moon in the sky of the horizon diagram at bottom. Use direction words (like north, west, etc.) and estimate its altitude in degrees. Northwest with an altitude of about 45 degrees. Page 6 – The Witness and the Detective If we know the moon's position in the sky and its phase, we can estimate the Time . In general, knowing any two of the following three things allows us to estimate the third: 1. moon's position in the sky 2. moon’s phase 3. the time Part II: Visualizing Phases We can determine the appearance of the moon based on the orientation of the moon and sun with a simple heuristic. In the figure below, bisect the moon twice . a) Draw a line (perpendicular to the direction of sunlight) that shows the half of the entire moon that is illuminated and shade the shadowed region. b) Draw a line (perpendicular to the Earth-moon line) that shows the half of the moon visible for an observer on earth. c) Mark the region that is both visible from earth and illuminated by the sun. That region will be the phase of the moon we on earth see. NAAP – Lunar Phase Simulator 4/10

We normally draw the phases of the moon with the terminator (the dividing line between light and shadow) from the north pole to the south pole of the moon. This is how the moon would be seen if it were on the observer’s meridian. We can use the drawing above to determine the amount of illumination and whether it is on the left or right hand side of the moon. Use the drawing above to draw the appearance of the moon in the box below. Waning Gibbous Earth – Moon – Sun Geometry Click on the option labeled show angle – which graphically displays the angle between the direction of the sun and moon. Now drag the moon around the sun to a variety of different locations and note the appearance of the Moon Phase. Describe how the value of the angle correlates with the appearance of the moon. As the angle increases, so does the amount of moon that is being illuminated. On the other hand, as the angle decreases the amount of the moon being illuminated also decreases. Each row on the following table shows diagram of the earth-moon system. For each diagram, find the age of the moon at that position (that is, the time passed since new moon), its phase, and it’s percent illumination. Finally, make a sketch of its general appearance. You will need to take into account the orientation of the sunlight – it is different in each diagram from the orientation in the applet. The first row is completed for you. You may need to rotate your paper and hold it up to the screen to check your answers. NAAP – Lunar Phase Simulator 5/10 Illuminated

Moon Geometry Age Phase Percent Illumination Sketch 11 days, 9 hours Waxing Gibbous 88% 22 days, 2 hours Third Quarter 50.3% 3 days, 16 hours Waxing Crescent 14.6% NAAP – Lunar Phase Simulator 6/10

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18 days, 10 hours Waning Gibbous 85.3% 7 days, 9 hours First Quarter 50% Rising, Setting, and Meridian Times When observing the moon one thing we might like to know in advance is when it is visible – what time it sets, rises, and crosses the meridian (or transits). The applet can help find these times. Example 1: What is the meridian crossing (transit) time for a new moon? Move the moon to its new position. Rotate the earth until the moon is centered on the meridian (the observer should be located on the earth directly opposite the moon) . For finding transit times it helps to change the perspective of the horizon diagram (by clicking and dragging on it) so that we are looking straight down on the diagram. Note that the transit time of the new moon is 12:00 PM (noon). Complete the rest of the meridian times in the table below. Rising Meridian Crossing Setting New 6:00 AM 12:00 PM 6:01 PM NAAP – Lunar Phase Simulator 7/10

Waxing Crescent 9:07 AM 3:01 PM 9:15 PM First Quarter 12:03 PM 6:01 PM 12:12 AM Waxing Gibbous 3:43 PM 9:45 PM 3:32 AM Full 6:20 PM 11:54 PM 6:00 AM Waning Gibbous 9:15 PM 5:58 AM 9:43 AM Last Quarter 12:21 AM 6:07 AM 12:17 PM Waning Crescent 3:04 AM 9:12 AM 3:00 PM Example 2: What is the setting time for a full moon? First we move the moon to the full position by dragging it, or selecting ‘Full Moon’ in the phase name drop down list. Next, click on and rotate the earth while keeping an eye on the horizon diagram in the lower right corner. Rotate the earth until the moon just disappears below the western horizon. You should verify that this occurs at 6:00 AM. Complete the rest of the rising and setting times in the table above. Describe the relationship between the values of the meridian times and the rising and setting times in your table. There is approximately 6 hours from rising to meridian crossing, then 6 more hours to setting. As the moon moves from one of the phases above to the next, the times increase by approximately 3 hours. NAAP – Lunar Phase Simulator 8/10

Part IV: Lunar Phases in the Horizon Diagram Complete the following table. You are encouraged to visualize the solutions in horizon diagrams drawn on scratch paper or in your head and then use the simulation to check your answer. Time Location Phase A Noon First Quarter Eastern Horizon B 3 pm First Quarter East C Midnight First Quarter Western horizon D 9 pm Waning Gibbous Eastern Horizon E 3 am Waning Gibbous Southwest F Midnight Waxing Gibbous West G Noon Waxing Crescent Southeast Close the Moon Phases and the Horizon Diagram Simulator and return to the Lunar Phase Simulator and answer each of the following questions. The figure below shows the moon and sun on a horizon diagram. What is the phase and what is the time of day depicted? What time did the moon reach its highest point in the sky? The moon is a waning crescent. The depicted time of day is noon. The moon reached its highest point in the sky at 3am. NAAP – Lunar Phase Simulator 9/10

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In the figure above, draw and label the moon’s location 48 hours later. Will the moon be visible at noon 14 days later? No Explain your answer: At its current point, the moon is almost to its new phase. Once 14 more days pass, it will be close to a full moon. At a full moon, the moon rises at approximately the same time the sun sets and vice versa. Therefore, the moon would not be visible at noon. Draw and label the full moon and sun at 6:00 A.M. on the figure below. (If necessary or useful, draw an arrow to one or both spots.) NAAP – Lunar Phase Simulator 10/10 The red dot resembles the moon 48 hours later Sun Moon