I find that many students believe that Moon always rises at sunset and
sets at sunrise. This activity is designed to build a a
understanding of the relative positions of Earth, Sun, and Moon
associated with the various phases of Moon as seen from Earth.
NOTE: A lunar month is about 29.5 days, one revolution around Earth
takes 27.3 days.
My practice has been to have students copy onto blank paper as I draw
freehand on an overhead transparency. If you prefer, you may make
a transparency of the student worksheet
and have students copy on blank
paper or individual copies of the worksheet.
Presentation:
After each step has been presented, make a quick check of the class to
insure that each has the idea and is staying with you.
Now! Everyone has a pencil and prepared (name etc.) paper,
true? Ok.
This line represents Earth [drawing or indicating the horizontal line
in center]. As it normally appears to us, Earth is flat and I'm
always in the center. [draw stick figure etc.] Here's my house,
and I have a tree in my yard.
The sky is a bowl over head [drawing circle]. The time of day is
sunset [write "sunset" above the right end of "Earth"].
Remember, while you are watching Sun set, someone on the other side of
Earth is watching Sun rise. [Rotate the drawing 180o and
draw another stick figure. write "sunrise" above the left end of
"Earth".]
[Rotate the drawing to original position.] If Sun is setting, and
Moon is at new phase, where in the sky will Moon be?
Since at new moon Moon is in the same direction as Sun, Moon will set
at the same time Sun sets. [draw circle at the right end of "Earth" and
darken it completely.] We do not see any of the lighted half of
Moon from Earth.
About half a week later, what is Moon's phase? Right, it will be
waxing crescent (waxing means "getting bigger"), and it will be in the
southwest sky. [draw a circle at
about 45o darken all but a crescent on the side toward
Sun.] Now we see a
small part of the lighted half of Moon from Earth.
About one week after new moon, what is the phase? Right, it will
be first quarter phase, and it will be high in the south, even though
you see a "half moon", it is the end of the first quarter of the lunar
month. [Draw a circle at the top, darken the left half.] Now we
see half the lighted half of Moon from Earth.
A week and a half after new moon, what is the phase? Right, it is
waxing gibbous, and it will be in the southeast sky at sunset. [Draw
the circle and darken only a crescent.] Now we see most, but not all
the lighted half of Moon from Earth.
Two weeks after new moon, the phase is? Yes, full moon, since it
is in the opposite direction from Earth as Sun, at sunset Moon will
rise. [Draw circle at left end of "Earth"] Now we see all of the
lighted half of Moon from Earth.
Two and a half weeks after new moon, the phase is? Right, waning
gibbous (waning means "getting smaller"). And where is it in the
sky at sunset? It's not
in
the sky? Moon will not rise till some time after Sun has
set. But your opposite, on the other side of Earth, who is seeing
Sun rise also sees the waning gibbous moon in the southwest.
[Rotate the diagram, draw the circle and darken a crescent on the side
away from Sun.]
Three weeks after new moon, the phase is? Yes, third quarter
phase, meaning that three quarters of the lunar month have
passed. And where is Moon? At sunrise Moon is high in the south.
[draw the circle and darken the right half.]
Three and a half weeks after new moon, now the phase is? Yes,
waning crescent. Where? Southeast at sunrise. [draw the circle and darken
all but a crescent.]
About four weeks after new moon, what phase is it? That's
right! It is new moon again! the end of one lunar month and the
beginning of the next lunar month. [Pointing to the first
circle.] And at sunrise,
as Sun is rising Moon is also rising. Even though you will not be
able to see it, Moon will be in
the sky all day.
