Lab 2 Lunar Phases

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Washington State University *

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MISC

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Astronomy

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Dec 6, 2023

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Lunar Phases Leah Andersen Remember to type your answers in blue text Part 1: Background Information Thoroughly read all the material found in the links listed under the Background Material of the NAAP Lunar Phases lab. All the concepts covered in these pages are used in this lab and you will need to be familiar with them before you begin. Question 1 : Is there a side of the moon that never receives sunlight? Explain. Question 2: The following sketches of the moon's appearance were made over about four weeks. Identify the phases and put them in the correct chronological order, starting with the phase labeled 1. Picture Order Phase Picture Order Phase NAAP – Lunar Phase Simulator 1 /11 There is no permanent dark side of the moon because the moon always rotates.

A D B E C F Question 3: From the perspective of an observer above the North Pole, the moon moves counter-clockwise in its orbit around the earth. In the diagram below, the sun's light is coming in from the right and the moon's location is marked at six points along its orbit. These are the points where the moon was located when the sketches on the previous page were drawn. Identify each position with the letter of the corresponding sketch. NAAP – Lunar Phase Simulator 2 /11 6 Waxing Cresent 2 First quarter half moon 3 Waxing Gibbous 5 Waning Gibbous 4 Full moon 1 Waning crescent D E C F A B

Moon Earth sunlight Part 2: Visualizing Phases You will need to use a drawing tool to insert shapes into the picture for the next question. Here is how I would do it, although I am no expert in using Word: To draw a line within the image of the moon, click ‘Insert’, select ‘Shapes’, and then select the ‘Scribble’ option under Lines. Place your cursor where you want to begin your line, hold down left click, then drag your cursor to the end point of the line and release. This places a line segment inside the picture. You can easily erase and try again by selecting Ctrl Z. If you cannot get the drawing tool to work, just create a text box and describe what you wanted to draw. Question 4: We can determine the appearance of the moon based on the orientation of the moon and sun with a simple diagram. In the figure at the top of the next page, you will bisect the moon twice . The view in this figure is from the perspective on an observer high about the North Pole, and is not to scale. a) Draw a line (perpendicular to the direction of sunlight) that shows the half of the moon that is illuminated by the sun. b) Draw a line (perpendicular to an imaginary line connecting the Earth and moon) that shows the half of the moon visible for an observer on Earth. c) Note the region that is both visible from Earth and illuminated by the sun. That region will cause the phase of the moon we see on Earth. NAAP – Lunar Phase Simulator 3 /11

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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 figure above to determine the amount of illumination and whether it is on the left or right side of the moon, as seen from Earth. Use this figure to draw the location of the terminator in diagram of the moon in the box below. Remember this is how an observer on Earth would see the moon. What side of the terminator is illuminated by the sun, the right or left side? Open the Moon Bisector Demo and use the simulator to check your answer to the above problem. Part 3: Working with the Lunar Phase Simulator The items below will help familiarize you with the controls and usability features of the simulator.  If you have not already done so, launch the NAAP Lunar Phase Simulator  The main panel has sunlight, the earth, and moon. The earth and moon can be dragged with the mouse.  Below the main panel, there are animation controls. The moon and earth can be dragged.  The increment buttons move both the moon and earth by the specified time.  The Moon Phase panel shows the current moon phase. Drop down menus will jump to a predefined position. Note that the phases, such as crescent and gibbous, are broader than the particular point chosen by the presets.  The Horizon Diagram panel displays the point of view of the observer (and you are a second observer looking down on that observer).  The observer’s horizon diagram can be dragged to allow for the most convenient viewing orientation.  The sun and moon on the globe can be dragged around.  In the Diagram Options panel, the show angle option shows the earth-moon-sun angle. The phases are technically defined in terms of this angle. NAAP – Lunar Phase Simulator 4 /11 Right

 In the Diagram Options panel, the show lunar landmark option draws a point of reference to more easily observer lunar rotation and revolution.  In the Diagram Options panel, the show time tickmarks option displays the time of day of the observer. Earth – Moon – Sun Geometry Question 5: 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 appearance of the moon correlates with the value of the angle. Question 6: Each row of the table on the following page shows a 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), the phase, and the percent illuminated. There will be a range of acceptable answers for the age and percent illuminated for the crescent and gibbous phases. Finally, make a sketch of the moon’s phase using the ‘Scribble’ drawing tool. To do this, sketch the terminator and then scribble in the dark part of the moon. It does not need to look perfect! Again, if you cannot use the drawing tool you can describe what you wanted to draw. When determining the phase, you will need to take into account the orientation of the sunlight. One row is completed for you. Moon Geometry Age Phase Percent Sketch NAAP – Lunar Phase Simulator 5 /11 The Wider the angle the more the moon is closest to being a full moon, the narrower the angle, the more the moon is closest to being a new moon.

Illuminated 11 days, 1 hour Waxing Gibbous 85.4% 22 days, 3 hours Third quarter 50% 4 Days Waxing Cresent 22% 14 Days, 13 hours Full moon 100% NAAP – Lunar Phase Simulator 6 /11

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24 days, 20 hours Waning cresent 23% Rising, Setting, and Meridian Times Question 7: 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 Lunar Phase Simulator can be used to 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. When 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 crossing times in the table below. Example 2: What is the setting time for a full moon? First we move the moon to the full position by selecting ‘Full Moon’ in the Moon Phase 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 for the full moon. Complete the rest of the rising and setting times in the table below. Rising Meridian Crossing Setting New 6 am 12:00 PM 6pm NAAP – Lunar Phase Simulator 7 /11

Waxing Crescent 9am 3pm 9pm First Quarter 12 pm 6pm 12am Waxing Gibbous 3 pm 9pm 3am Full 6 pm 12am 6:00 AM Waning Gibbous 9 pm 3 am 9 am Last Quarter 12 am 6 am 12 pm Waning Crescent 3 am 9 am 3 pm Question 8: In general, describe how the rising and setting time of the moon changes as the phase cycle progresses NAAP – Lunar Phase Simulator 8 /11 There is a time difference of three hours between the time it rises and the time it sets every day. The time moves forward by three hours but each phase has twelve hours between the times of rising and setting.

Part 4: Lunar Phases in the Horizon Diagram This module also contains another simulator especially for gaining insight into the lunar phases in the horizon system. Open the Moon Phases and the Horizon Diagram simulator and follow the guidelines below to gain familiarity with the simulator. Begin by unchecking all options and setting the observer’s latitude to 48 degrees.  Click the option entitled show ecliptic band . Since the ecliptic can be as much as 23.5º away from the celestial equator and the plane of the moon’s orbit is inclined almost 6 degrees to the plane of the ecliptic – the moon can be located in a band almost 60º wide in the sky. For simplicity in this lab, we will (incorrectly) assume that the moon is always located on the celestial equator. Unclick show ecliptic band.  Eight distinct locations for the sun corresponding to 8 distinct times are identified. Click show sun and show time and use the slider to manipulate the sun’s position. Place the sun at the appropriate location for each of the following times: 6 am, 9 am, noon, 3 pm, 6 pm, 9 pm, midnight, and 3 am.  Place the sun at the noon position (position 3). Click show moon and place the moon at position 3 as well. Click show phase and show phase on moon disc . Note that when the moon is one position east of the sun, its phase is waxing crescent. When the moon is two positions east of the sun its phase is first quarter. Move the moon through the remaining phases of the cycle. There are two general rules for solving problems in the horizon system.  The time is denoted by the position of the sun.  The phase of the moon is denoted by how many steps (out of the 8) the moon is east of the sun. Question 9: Complete the table on the following page using the Moon Phases and the Horizon Diagram simulator. Set the latitude of the observer to 48°N. You should try to figure out the answers in horizon diagrams drawn on scratch paper or visualized in your head and then use the simulator to check your answer. NAAP – Lunar Phase Simulator 9 /11

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sun moon Time Phase Location A Noon Waning Crescent Southwest B 3 pm Waxing Gibbous Eastern Horizon C 6 am Third Quarter South D 9 pm First Quarter Southwest E 3 am Waning Crescent Eastern horizon F 6 pm Full Moon Eastern Horizon G 12 am Waning Gibbous Southeast Close the Moon Phases and the Horizon Diagram simulator and return to the Lunar Phase Simulator to answer each of the following questions. Question 10: The figure below shows the moon and sun on a horizon diagram. What is the phase of the moon in this diagram? What is the time of day depicted? What time did the moon reach its highest point in the sky? Question 11: Will the moon be visible 14 days later at the same time of day depicted above? Explain your answer: NAAP – Lunar Phase Simulator 10 /11 12 am/ noon noon Waning Crescent No because the moon will be in a different phase. The moon will be underneath the observer so they will not be able to see it.

Summary/Conclusion (5 points): Give a detailed explanation of what causes the lunar phase cycle, and describe why the rising and setting times of the moon change as the cycle progresses. NAAP – Lunar Phase Simulator 11 /11 When the moon rotates there are certain parts that are illuminated by the sun. They are called the phases of the moon. The phases are made by the moon changing positions and the earth and sun as the moon orbits earth. The rise and set times change as the moon changes its position around the earths orbit. The earth has to catch up to the moons new location.

Lab 2 Lunar Phases

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