Making the observations
This project involves observing the Moon during the course
of a lunation (the period from New Moon through Full Moon and
back to New Moon again), much as the ancients did. It will require
your making observations for a few minutes each day, for several
weeks, and a few additional observations at the beginning of the
following lunation. You should make each observation around Sunset.
Although you can start observing any time, it is easiest if you
start about the time of New Moon. Check the newspaper or a calendar
for the dates of New Moon this semester, or use John Conway's
simple calculation as given on the web page What
is the age of the Moon? to estimate the time of New Moon.
If you have a JavaScript-aware web browser, you can also try the
Moon
Phase Calculator that I picked up off the net. It will tell
you how long it will be until the next full moon (the new moon
is 14 days earlier). No guarantees on this one.
As the Sun sets, the first thing to do is to estimate the angle
between the Moon and the Sun. To estimate the angle between the
Moon and the Sun, point one arm towards the Moon and the other
towards the Sun. Imagine that your arms are lying along a giant
protractor, as shown in the picture. Try to guess the angle that
your arms are making to the nearest 10 degrees. Record this information
in the table.
If you are observing after Sunset, then you should estimate
the angle between the Moon and where the Sun disappeared from
view (the Sunset point), and add 15 degreees to this for each
hour after Sunset. You will have to do this later in the lunation,
because the Moon will not rise until after Sunset during the latter
part of the lunation. (Eventually it will rise so late that you
will have already gone to bed--when this happens, wait until the
start of the next month to complete your observations; but if
you are a night owl or get up really early in the morning, you
may catch the Moon near sunrise.).
Next, make a sketch in one of the circles on this handout showing
the shape of the Moon as you see it. Sketch the markings on the
Moon as best you can (the "man in the Moon"). Draw an
arrow outside the circle that points towards the Sun. Mark the
date.
Finally, choose the star map from amongst the ones attached to
this handout that best represents the stars in the sky as you
see them on this date (you may want to wait a bit until the sky
gets dark enough to see the stars). Note the position of the Moon
relative to the stars, and plot its position on the star map.
Hints: The star maps are marked with the appropriate dates and
times. You should hold the chart so that the direction you are
facing is DOWN. If you are looking overhead, hold the chart over
your head so that North is at the North, etc. Also, note that
the Moon is always going to be within about 5 degrees of the Ecliptic.
This will help you to identify the stars in the sky with those
on the chart.
Please be sure that you make observations over an entire lunation.
In particular, your last observation should be at least 30 days
after the first, and a few extra ones after that won't hurt.
Interpreting your results
Now you are in a position to answer the following questions:
1. Observed at the same time each night, in which direction does
the Moon appear to move from night to night: From East to West,
or from West to East?
2. From the angles you have written down, approximately how many
degrees per day does the Moon appear to move, relative to the
Sun? Hint: Compare the angle from Moon to Sun for your first observation
with that for your last observation. The Moon will have travelled
one complete circuit around the sky (360 degrees) relative to
the Sun when it reappears at the same phase. How
many days does this take? How many degrees per day? (This is the
Synodic month, which we studied in class.)
3. Now look at your star map. There are four maps which follow
the Ecliptic around the sky. If you were to cut them out and paste
them together, they would form a band around the Ecliptic. The
position of the Sun is located by date on each map. To use the
maps, imagine that the Sun is just setting; turn the map about
30 degrees clockwise and hold the map so that the Sun is on the
horizon. Identify the stars above the horizon by comparing with
the map. Each day, plot the position of the Moon on the map. Relative
to the stars, how many days does it take for the Moon to go
once around the sky and get to the same position among the stars?
How many degrees per day is this? (This is the Sidereal month.)
4. How does the shape of the Moon depend on the angle between
the Moon and the Sun, according to the sketches you made of the
Moon's face?
5. Interpret all of these results in terms of what we learned
in class.
For full credit, be sure to turn in all graphs, calculations,
and other information that you used in doing this assignment.
Table to record results
| Date | Moon-Sun Angle | Date | Moon-Sun Angle | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg | |
| ___/___/___ | __________deg | ___/___/___ | __________deg |
