Phases of the Moon
INTRODUCTION:
The phase of the Moon and the time it is up vary over the month. Is there a connection? In this lab we will observe the Moon
over a period of one month, recording the phase and the time of Moonrise. You will analyze your observations, and check
for patterns, compare them with accepted values, write up the results in a lab report format. Include all of your observations
and your copy of the map of the Moon along with calculations in your lab write up.
I. MODELING THE PHASES OF THE MOON:
The phase of the Moon depends on the angle between the Sun and the
Moon as seen from the Earth One half of the Moon is always illuminated
by the Sun (unless there’s a Lunar Eclipse), however, the illuminated half
is not always fully facing the Earth. (See Figure). As the Moon orbits
the Earth we see a different amount of illuminated and dark Moon.
You can simulate the phases of the Moon using a golf ball for the Moon,
a lamp for the Sun and your head will represent the Earth. Hold the ball
in front of you so that the lamp illuminates half of it – then turn with the
ball still in front so you see a different amount of the illuminated side of
the ball. Where are you facing to you see a “Full Ball” or a “New Ball”?
Where do you see a “Quarter Ball” Note: when doing this model, assume
North is “Up” then the Earth both rotates and spins to the left and the
Moon’s orbital motion is leftward (how can you confirm this?). Does
the side (East or West) of the Moon illuminated depends on the phase?
II. OBSERVING THE PHASES OF THE MOON
1) Using supplied map of the Moon, find and indicate the positions of the listed lunar maria, craters, etc. (You will
turn this in with your lab report) For help, see http://www.oarval.org/MoonMapen.htm which has a labeled
map of lunar craters and maria: Note: when drawing the Moon, it is helpful to know the names of some of the most
recognizable features on the Moon (e.g. Seas of Tranquility, Crisis, Serenity, and Tears plus the Ocean of Storms).
2) During the next month you will observe the Moon on twelve different days (or nights) shortly after moonrise (i.e.
within 2 hours of moonrise). Record the date, time, and location of observation; estimate the altitude of the Moon
above the Eastern Horizon, and its apparent phase (based on appearance). Also draw the Moon as it appears,
include the large maria and the terminator (the line separating the bright side from the dark side) – Note: indicating
which maria are closet to the terminator will make it easier, so include as many features as you can!
3) For one of the above observations, measure the altitude and azimuth shift for the rising moon. Start when the Moon
is not completely above the horizon(it will have an altitude of 0 and an azimuth shift of 0), every four minutes
measure the altitude and the change in azimuth - for ten total observations (36 minutes).
III. ANALYSIS OF DATA:
After you have collected your data on the Moon you must analyze it. The analysis will entail making a number of
measurements from your drawings and recorded observations. The better quality your observations the easier the analysis
will be. These steps should be done in order since some depend on previous steps.
1) Plot the altitude and azimuth shift of the rising Moon as a function of time. How many degrees per minute does it
rise?
2) Using the information from step 1, calculate the time of moonrise for each of your observations.
3) Estimate the full moon percentage for each observation using the grids on the observing sheet. Each box is 1% of a
full moon. Count the number of full boxes, and estimate partially full boxes. The total number will equal the
percentage full for each measurement. Compare this measure with the lunar phase.
4) Obtain plots of the times of moonrise and full moon percentage for this school term and indicate the days of Full,
New and Quarter moons – also mark your measurements on the plots. You may find information at this website:
http://aa.usno.navy.mil/data/docs/RS_OneYear.html
IV. QUESTIONS TO ANSWER IN YOUR REPORT:
These questions are to be addressed in the lab write up – discuss these thoroughly. You do not need to write them up as
questions and answers, but discuss each point in your write up.
1) Discuss the plots of altitude and azimuth of the rising Moon, what is the rate of rise for the Moon? How does the
azimuth shift over time? Are the rate of rise and rate of azimuth shift constant? Explain your observations using
information about the rotation of the Earth and the Moon’s orbit (you may include a diagram if you wish)
2) Refer to your plots: how well do your observations match the published values for moonrise and full moon
percentage? What are the minimum, maximum and average errors for your measurements of moonrise and
percentage? Are the errors the same for both types of measurement? Are these errors acceptable – why do you
think so? What could you do to reduce these errors?
3) During the period of observation does the time of moonrise vary with the phase? Make a table listing moonrise
times for this school term for New, First Quarter, Full and Third Quarter Moons. Is this what you expected? Why
or why not?
4) How much does the time of moonrise vary from one day to the next? Is it always the same amount (hint: check the
shape of the moonrise plot – how does it answer this question?). If not what are the minimum, maximum and
average amounts? Explain this variation based on the rotation of the Earth and the Moon’s orbit.
5) Is there a moonrise everyday? How do you explain this? (Hint: check around Third Quarter – what happens then?)
6) Which side of the Moon illuminated (e.g. East or West) for a First Quarter? How about a Third Quarter? Based on
your model of Lunar Phases, does this make sense? Explain how you could determine if the Moon is waxing or
waning based on this observation.
Identify the following features on the image of the Moon.
For assistance, you may refer to the website http://www.oarval.org/MoonMapen.htm
1 Mare Frigoris (Sea of Cold)
2 Mare Imbrium (Sea of Rains)
3 Sinus Aestuum (Bay of Seething)
4 Sinus Medii (Bay of the Center)
5 Mare Vaporum (Sea of Vapors)
6 Mare Serenitatis (Sea of Serenity)
7 Mare Tranquillitatis (Sea of Tranquillity)
8 Mare Crisium (Sea of Crises)
9 Mare Fecunditatis (Sea of Fecundity)
10 Mare Nectaris (Sea of Nectar)
11
12
13
14
15
16
17
18
19
20
Mare Nubium (Sea of Clouds)
Mare Humorum (Sea of Moisture)
Mare Cognitum (Known Sea)
Oceanus Procellarum (Ocean of Storms)
Sinus Roris (Bay of Dew)
Sinus Iridum (Bay of Rainbows)
Crater Tycho
Crater Copernicus
Crater Kepler
Crater Plato
Moon Observation Sheet
(Please make copies: one for each observation)
Date/Time of Observation_______________________ Location: ________________________
Altitude above Eastern Horizon: ____________ Apparent Lunar Phase______________
Notes: ___________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
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Moon Observation Sheet
(Please make copies: one for each observation)
Date/Time of Observation_______________________ Location: ________________________
Altitude above Eastern Horizon: ____________ Apparent Lunar Phase______________
Notes: ___________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________