# Moon Phases and Eclipses

Suggested Grade Level(s): Middle School

Estimated class time: one class period

# Summary

An essential factor in the understanding of the gravitational bending of
light was the discovery that the gravity of the sun's mass could cause a
distant star to appear as if it was actually in a different location.
Einstein predicted that the light from a far away star would be bent,
but it could only be seen during a solar eclipse when the light of the
sun between Earth and the distant star did not blind the observer. In
this activity you will create a solar eclipse, a lunar eclipse, and
learn more about why the moon appears differently from one night to the
next.

# Objectives

-   Students will demonstrate both a solar and lunar eclipse and explain
    the differences and similarities of both.

-   Students will explain why Einstein used a particular solar eclipse
    to demonstrate that extreme gravity can bend light.

# National Standards

**National Science Standards**

-   NS.5-8.1 SCIENCE AS INQUIRY

> As a result of activities in grades 5-8, all students should
> develop\--

-   Abilities necessary to do scientific inquiry

-   Understandings about scientific inquiry

```{=html}
<!-- -->
```
-   NS.5-8.4 EARTH AND SPACE SCIENCE

> As a result of their activities in grades 5-8, all students should
> develop an understanding

-   Structure of the earth system

-   Earth in the solar system

# Knowledge Prerequisite

-   Students should be familiar with the concepts of the sun-earth-moon
    system and should also be aware that other stars exist far beyond
    our solar system.

-   Students should have read the 1919 Cosmic Times articles about
    Einstein's predictions.

# Materials

-   Photographs or slides which show the real moon in several different
    phases

-   Plastic foam ball about the size of a grapefruit (to be the moon)

-   Pencil or short dowel rod about the size of a pencil

-   A bright light such as a lamp without the shade (to be the sun)

-   A very small, dim light such as those found on a key chain (to be
    the distant star)

-   Paper and a pencil to record what you observe

-   A very dark room

-   A camera to photograph a panorama of your horizon

# Procedure:

### I. Engagement 

Ask the students to draw a picture of the moon showing the way it looked
the last time they remember seeing it. This will probably produce
several different views. Show the students the photographs of the moon
phases in no particular order and ask them to write why they think the
moon looks different at different times. Allow the students to share
their thoughts with the class. A very common misconception is that the
shadow of the earth causes the moon phases. Don't contradict that
thought, but do draw a picture on the board which shows the Earth, its
shadow, and the moon in various positions on its trip around the earth.

### II. Exploration

Explain that the ball will represent the moon and the lamp will be the
sun. Their eyes will be an observer from earth. Allow them to experiment
with the ball and lamp to recreate the condition they drew in the first
activity. Then ask them to reproduce at least two other conditions
similar to the images you showed them in the photographs.

### III. Explanation

Remind the students that when scientists do research, they try to follow
an experimental plan, which can be repeated by other researchers in
their own laboratories. Now we will all try to complete the same
procedure to see if we can find an explanation for the phases of the
moon.

Set up the light (turned off) in a position so that you can stand about
2 meters in front of it, have enough room to hold your arm out straight
in front of you, and be able to rotate a full 360-degree circle. Push
the pencil into the foam ball so that it makes a little stem handle to
hold the ball up enough to keep your fingers out of the ball's shadow.
Place the smaller light on the opposite side of the lamp from you and
high enough so that it appears to you to be about 1cm above the lamp
bulb. Now turn the bright bulb on.

Stand facing the bright light holding your moon ball straight out in
front of you. Your eyes are an observer on earth looking at the sun.
Very bright isn't it? Can you see detail on the moon ball? Can you see
the little distant starlight? (1) Now slowly raise the moon ball until
its shadow falls across your face. This is a SOLAR ECLIPSE! The sunlight
is blocked by the shadow of the moon, which is located between the sun
and the earth. In this eclipsed position, can you now see the smaller
light peaking from behind the lamp? Before, the lamplight totally
overpowered the smaller light, but now your eye or telescope can see it.
However, can you see any of the lighted side of the moon? (2)This is
called the NEW MOON stage and a solar eclipse can only occur at this
phase. Does the shadow of the moon ball cover all of your face? (3)
Einstein needed to find a solar eclipse occurring in a place where
people could reasonably visit and he needed a clear day to observe the
sky for the few minutes the moon shadow blocked the bright sun. A very
rare event indeed!

Slowly turn to your left just enough so that a little sliver of light
appears along the edge of your moon ball. This stage of the moon cycle
is called the WAXING CRESCENT and occurs about 3 days after the new moon
stage. Continue to turn to your right until half of the moon ball facing
you is lit and half is dark. This stage is called the FIRST QUARTER moon
because you can see only half of the half or a quarter of the moon.

Continue turning to your left until almost, but not all, of the visible
moon is lighted. This "fat" stage of the moon is called the WAXING
GIBBOUS.

Finally continue turning to the left until all of the lighted side of
the moon is visible. This we know is the FULL MOON stage. You may need
to hold the ball up above your head a little for the light to actually
shine on the ball. If you lower the moon ball until your own shadow
covers it, you have created a LUNAR ECLIPSE. This happens when the moon
is in the Earth's shadow. Raise and lower the moon a few times to be
sure that you understand the Full moon stage and the lunar eclipse.
Notice that your body (the earth) casts a much larger shadow than the
earth did. The moon can move across the sky for a longer time while
still remaining in the earth shadow and everybody on the nighttime side
of the earth can see the eclipse. Unfortunately Einstein could not use a
lunar eclipse to test his theory. Why not? (4) Think about the
difference between the mass of the moon and of the sun.

Continue turning until you pass through the WANING GIBBOUS stage, the
THIRD QUARTER, the WANING CRESCENT, and finally back to the NEW MOON
STAGE. While facing the bright lamp, practice raising and lowering the
moon a few times to simulate the SOLAR ECLIPSE. Only during the SOLAR
ECLIPSE can you see the smaller, dimmer light from beyond the sun.

Repeat the experiment, but draw a picture of the moon in each of its
phases.

Now write a short paragraph to explain why Einstein needed to have a
solar eclipse in order to see the apparent displacement of a distant
star because the mass of our sun bent the light coming from it

### IV. Extension and Evaluation

Using the date for the moon phase when you are doing this activity, ask
the students to predict the moon's appearance on several upcoming dates.
For instance, if the full moon was on Jan. 3, what would the moon look
like on Jan. 19 or 25? You can also ask the students to predict the date
of a future phase, for instance, "When should we expect the next waxing
crescent if today is the full moon?" Do these predictions as an in-class
activity.

If you begin your space unit with the moon, you can have the students
keep a moon log for the remainder of your time in space or for at least
one month. Many resourceful students will find web pages, which will
show the moon phase for a particular date. They can produce a complete
moon log for the month, regardless of the weather, in one sitting at
their computer. You can use the computer data to see if it matches their
predictions, but encourage them to actually look at the sky. If they do
their logs at the same time of evening each day, they will realize that
not only the phase of the moon changes, but also its position in the
sky. If the students have access to a digital camera, they can make a
photograph of the panoramic horizon at their home and then DRAW the moon
on successive nights at the same time.

# Teacher Notes

1.  The sunlight is very bright because it would be daylight for your
    observer, possibly close to noon. The moon is not very visible and
    you can't see the little light at all because the brightness of the
    lamp overpowers everything.

2.  No, because it is facing away from you.

3.  Probably not, because the ball is small and does not cast a large
    shadow. The real moon is also small and does not cast a very large
    shadow on the earth. The chance of a solar eclipse occurring at any
    given spot on the earth is fairly rare. The rotation of the earth
    also means that the moon shadow does not stay in one place more than
    a few minutes.

4.  Light from a distant star passing close by our very small moon would
    not be deflected enough to measure because the mass of the moon is
    so little. The mass of the sun was large enough to cause a
    deflection, although very small.

5.  Remind the students that this activity creates a model of the earth-
    moon-sun system. Models often help us to understand a concept
    better, but they come with a danger of creating a mindset that may
    not actually represent what is real. The lamp in this model does NOT
    affect the light from the tiny laser beam.