Phases of the Moon & Eclipses
Setting up Stellarium for Use
Open Stellarium by double-clicking its icon on the Desktop. You will be presented with a depiction of the
current sky as seen from Towson facing south. By default, Stellarium does not render the local cityscape,
but the sky as shown here would otherwise be the sky as it would appear outside right now if we could
turn out all of the nearby lights and remove the nearby buildings.
Remove Celestial Information
Click on any star or object in the sky. Information about that celestial object appears in the upper-left
corner of your screen. This information is useful for future purposes, but for now it can be a little
confusing, so we’ll remove it by following these steps:
- Press the F2 key to bring up the Configuration window.
- Select the Information tab at the top of this window.
- Under Selected object information, select None.
- Close this window using the esc key on your keyboard or by clicking the × icon in the upper-right.
Verify Location and Time Zone
Next, let us verify that we are viewing the sky from Towson by looking at the information bar at the
bottom of your screen. It should read Earth, Towson in the lower left of your screen. The lower right
of your screen should indicate today’s date, time, and time zone (for example, 2019-09-0119:27:54
UTC−04:00 , see circled items at the bottom of the figure below). 1
If either the location or time zone are not correct, move your mouse to the lower left of your screen and
select the Location Window icon (you can also bring up this window by pressing the F6 key on your
keyboard) and use the following troubleshooting steps:
In the lower left, ensure that the Get location from Network checkbox is checked (circled). If this does not
change the location to Towson, do the following: - Search for Towson in the location listing (1 in the figure above)
- Click Towson, United States to change Stellarium’s location to Towson.
- Check and uncheck the Use Custom Time Zone checkbox until the Time Zone dropdown reads
America/New York. - Check the Enable daylight saving time checkbox.
- Verify the time and date ends with UTC−04:00 (if not, try checking Use Custom Time Zone and
select America/New York from the dropdown list.) - Check Use current location as default.
Should read UTC−05:00 during standard time and UTC−04:00 during daylight saving time. 1
Page 1
Name: _________________
Measuring a “Moonth”
Locate the Moon by opening the Search window (CTRL+F) and typing moon in the search bar, then the
Enter key. Stellarium will reorient your view and place the Moon in crosshairs. Press the space bar to
ensure Stellarium tracks the Moon at all times.2
Toggle the atmosphere off [A]. If the Moon is below the horizon, toggle the ground off with the G key.
Note that in the default view, the Moon appears much too small to easily determine its phase. Use the
scroll wheel on your mouse to zoom in to glimpse the Moon.
The Moon entered the New phase on August 30 2019 at 6:37 AM EDT. Let us return to this moment.
Pause time by pressing the K key. Open the Date/Time window [F5] and setting the date and time to
2019-8-30 6:37:0.
Turn on constellation stick figures [C] and names [V] and adjust your view to notice the Moon appears
near the Sun in the constellation Leo the lion.
Zoom in on the Moon to make note of the patter of bright stars nearby (you may wish to bring up the Sky
and Viewing Options menu [F4], go to the Sky tab, and toggle/adjust Labels and Markers to reveal star
names).
Make sure the Equatorial mounting is turned on by toggling CTRL+M and ensuring that the telescope
icon in the bottom menu bar is illuminated. This will compensate for the sky’s changing orientation as
Earth rotates and make our observations easier.
Using a piece of scrap paper, make a sketch of the Moon’s location with respect to the background stars
and the Sun. Be sure to note the starting date/time next to the Moon. This will help with the next steps.
Advance by one solar day with the + key (you can step backward one solar day with the - key as needed).
Continue advancing and note the Moon is now appearing to move eastward in the sky, going through its
phases as it does so.
Continue advancing time forward by days, then by hours and minutes until the Moon returns to its
original starting location with respect to the background stars in Leo (note the Moon won’t return to the
exact starting location due to its orbital tilt; just bring it as close to the starting location as you can). This
marks the end of the Moon’s sidereal period. Record this date time in the table below.
- Zoom out and notice the Moon’s position with respect to the Sun. Describe its phase at this point and
its location with respect to the Sun. - Record the date and time in the Sidereal end date/time column in the table above.
Start date/time Sidereal end date/time Synodic end date/time
2019-08-30 06:37
If for some reason the Moon is deselected or otherwise slips out of view, just repeat this step to find and lock up on it again. 2
Page 2
Advance time forward by days, then by hours until the Moon appears to have returned to its New phase
and close to its starting position relative to the Sun. Use your best judgment here - the Moon won’t return
to exactly the same distance from the Sun. (In fact, it will appear to be closer!). Make note of this date and
time in the Synodic end date/time column. - Approximately how much longer is the Moon’s synodic period than its sidereal period? _
- Why do the periods differ, and why does the Moon return to its starting position among the
background stars before it returns to its starting phase?
Predicting Lunar Phases
The diagram attached to this lab depicts the Sun, Earth, and the Moon in one of eight locations in its
orbit , as viewed from “above” Earth’s north pole. From this vantage point, the Moon appears to move in 3
a counter-clockwise fashion, as indicated by the arrows.
Cut out the cartoon of the guy on the east-west line. We will use this to represent ourselves standing on
the surface of Earth, with our Eastern and Western horizons stretching to our left and right, respectively.
We will now explore when the Moon is visible during a 24-hour period. As we will see, when and where
we find the Moon in the sky is closely associated with its phase. Let us explore the relationship between
these phenomena.
The Moon phase diagram is a useful tool in determining where the Moon is at a particular time of day
when the Moon is in a given phase.
For these steps, we will place our cutout over the Earth in the Moon phase diagram we created in Step 2.
Note that the Moon orbits counterclockwise (to the east) and Earth rotates counterclockwise (to the east)
as well. - For the following table, use your Moon phase diagram to determine the approximate times of
moonrise, moonset, and meridian crossing for each Moon phase. Use descriptive terms such as dawn/
sunrise, noon, dusk/sunset, evening, and midnight instead of times of day, because the actual times
will vary throughout the year..
Phase Moonrise Moon on Meridian Moonset
New
1st Quarter
Full
3rd Quarter
Not drawn to scale, obviously. 3
Page 3 - You observe a full Moon rising in the east. Which image shown best represents how the Moon will
appear as it is setting? - Which of the following could never happen?
a. An observer seeing a full Moon in the middle of the day (local noon).
b. An observer seeing a new Moon in the middle of the night (local midnight).
c. Both of the above observations are impossible for any observer to see. - You and your friend are walking home from a party one night and your friend asks you what time it
is. Neither of you are wearing a watch but you notice that the Full Moon is at its highest point in the
sky (crossing the meridian). Approximately what time is it? - For some reason you awake near dawn and notice that the Moon is halfway between the eastern
horizon and zenith. What is the phase of the Moon?
The July 2019 Eclipse
Let us return to Stellarium. This last July,
there was a total solar eclipse visible from
the Pacific Ocean (to have the best view of
this event (marked on the map)).
Let us simulate what it would have been
like to be on a ship at sea to witness this
eclipse.
Toggle the atmosphere [A] and ground
[G] back on, and return to the standard
azimuth mount [CTRL+M]. The telescope
icon at the bottom of your screen should
now be turned off and zooming out will
show the location of the Sun and Moon
with respect to the horizon.
Toggle off the constellations [C] and names [V].
In the Sky and Viewing Options window [F4], change the landscape to Ocean.
Open the Location window [F6] and change the latitude to S 17 0′ 0.00″ and longitude to W 109
0′ 0.00″ (Note: Stellarium is a little buggy here. You may need to use the up and down arrows next to
the lat/long to manually tick your way to the right location. Make sure the correct lat/long appear at
the bottom of your screen.) Check Use custom time zone and change to UTC-00:00.
Page 4
A B C D E
Set the date and time to 2019-7-2 16:30:0. As we can see, it is late morning and the Sun is low
above the northern horizon in the southern hemisphere’s winter sky.
Center on the Moon and advance time forward by pressing the L key a couple of times (but not too many
or else you’ll miss the eclipse.) - Zoom in as necessary and notice the Moon coming closer to the Sun. When the eastern limb of the
moon just touches the Sun, pause time and record the contact time to mark the beginning of the
eclipse (CT1). Record this time to the nearest minute.
Press K to allow the eclipse to proceed in real time. We will now watch the eclipse unfold in real time
(about 4 minutes in total). - Make note of the remaining contact times (CT2, CT3, and CT4) in the table above. As you do so, be
sure to zoom out and look around, noticing the sky getting darker. - Determine the time of mid eclipse by determining the duration in minutes between CT3 and CT2,
then adding half that duration to CT2. Record t