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Lunar Phase Simulator – Student Guide
Part I: Background Material
All background materials and the applets for this lab can be found at http://astro.unl.edu/naap/lps/lps.html. 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.)
How long does it take the moon to complete one cycle of phases, in days? ____________
If the moon is full today, what phase do you expect it to be at in a week? _____________
How about one month later? _____________
Many words in astronomy 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.
Picture Order Phase Picture Order Phase
A D
B 1 waning gibbous^ E
C F
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.
Page 3 – The Time of Day
Part II: Visualizing Phases
Question 1: 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.
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.
Open the Moon Bisector Demo and use the simulator to check your answer to the above problem.
Moon
Earth
sunlight
Part III: Working with the Lunar Phase Simulator
The items below will help familiarize yourself 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 more broad 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. 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.
Moon Geometry Age Phase Percent Illumination Sketch
11 days,
9 hours
Waxing
Gibbous
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.
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.
Question 4: Describe the relationship between the values of the meridian times and the
rising and setting times in your table.
Rising Meridian Crossing Setting
New 12:00 PM
Waxing Crescent
First Quarter Waxing Gibbous
Full 6:00 AM
Waning Gibbous Last Quarter
Waning Crescent
Time Phase Location
A Noon First Quarter B 3 pm First Quarter C First Quarter Western horizon D 9 pm Waning Gibbous E 3 am Southwest
F Midnight Waxing Gibbous G 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.
Question 6: 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?
Question 7: In the figure above, draw and label the moon’s location 48 hours later. Will
the moon be visible at noon 14 days later?
Explain your answer:
sun moon
Question 8: 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.)
Part V: Advanced Application
An article entitled Muslim Moon Sightings is attached. Write a short essay complete with diagrams describing how you were able to simulate the observations described in the article in the Lunar Phase Simulator.
