Module 1 – Lesson 2

Lesson 2: Moon Phases and Eclipses

Overview

This is the activity on “modeling the phases of the Moon” by Noreen Grice, with some modifications to blend with the format of our curricula lessons.  Using readily available materials, students, ideally 3-4, become the Sun, Earth, and Moon and simulate the phase cycle of the Moon.  For the second part, we emphasize the alignment that is needed to have solar and lunar eclipses and why they do not happen every month.

Learning Outcomes

• Name the 8 main phases and return to the Sun-Earth-Moon positioning that creates that phase.
• Replicate the 8 phases  on a small model.
• State the alignment needed for a lunar eclipse, a solar eclipse, and why we do not have eclipses every month.

Materials

• One styrene/styrofoam ball (baseball size)
• One small container of puff paint (optional) 
• Four-sided (pencil-size) stick; glue
• Several jingle bells
• Three students (for the Sun, Moon and Earth)
• Wood/foam mock-up of Earth-Moon system (see Figure 1.2.1 below)

Pre-assessment Questions and Discussion

Q.  What do we mean when we talk about the Moon going through phases?
A.  As the Moon orbits the Earth, we see different amounts of it lit depending on the Sun-Earth-Moon positions.

Q.  Who can name the main phases of the Moon?
A.  New, waxing crescent, 1^st quarter, waxing gibbous, full, waning gibbous, 3^rd quarter, waning crescent

Q.  Are there such things as the Moon blocking out the Sun’s light, or the Earth blocking the Sun’s light from reaching the Moon?
A. Yes, and they are called solar and lunar eclipses.

Text 

The Moon orbits Earth at an average distance of 382,400 kilometers, which is about the same as 238,000 miles. The lunar month is the 29.53 days it takes to go from one new moon to the next. During the lunar month, the Moon goes through all its phases.  Just like the Earth, half of the Moon is lit by the Sun while the other half is in darkness. The phases we see result from the angle the Moon makes with the Sun as viewed from Earth. 

We see the Moon only because it reflects sunlight. During the course of a month, the Moon circles once around the Earth. If we could magically look down on our solar system, we would see that the half of the Moon facing the Sun is always lit, but the lit side does not always face the Earth. As the Moon circles the Earth, the amount of the lit side we see changes. These changes are known as the phases of the Moon and it repeats in a recognizable pattern. 

At new moon, the Moon is between the Earth and the Sun. We see the side of the Moon that is not being lit by the Sun, or what is sometimes called the dark side of the Moon.  Although that side may be getting light that is reflected from the Earth, we can’t see it because the Sun is so bright.  When the Moon is exactly lined up with the Sun (as viewed from Earth), we experience a solar eclipse.  Since the Moon’s orbit is tilted with respect to the way the Earth lines up with the Sun, sometimes the Moon is too high or too low in its orbit to block the Sun.

After a new moon, and as the days go by, the Moon moves eastward in the sky away from the Sun. We see a bit more of the sunlit side of the Moon each night, right after sunset. A few days after a new moon, we see a thin crescent in the western evening sky. The crescent Moon waxes, or appears to grow fatter, each night. When half of the half of the Moon that faces us is illuminated, we call it the “first quarter” moon. This name comes from the fact that the Moon is now one-quarter of the way through the lunar month. From Earth, we are now looking at half of the sunlit side of the Moon from off to the side.  The “first-quarter moon rises at noon.”

The Moon continues to wax over the next week. Once more than half of the disc is illuminated from our point of view, it has a shape we call gibbous. The gibbous moon appears to grow fatter each night until we see the full sunlit face of the Moon. We call this phase the full moon. It rises in the East almost exactly as the Sun sets in the West, and sets just as the Sun rises the next day. The Moon has now completed one half of the lunar month.  If the Sun-Earth-Moon alignment is perfect, we would see an eclipse of the Moon.  However, because the Moon’s orbit is tilted, sometimes the Moon doesn’t pass through the Earth’s shadow.

During the second half of the lunar month, the Moon appears to grow thinner each night. We call this a waning moon. Its shape is still gibbous at this point, but grows a little thinner each night. As it reaches the third-quarter – sometimes called “last quarter” – point in its month, the Moon once again shows us one side of its disc illuminated and the other side in darkness. However, the “half of the half” that we saw dark at the first quarter phase is now the lit side, and what was the lit half is now the dark side.  The third-quarter moon is high in the daytime sky when the Sun is rising in the east, and sets in the west when it is around noon for us. This means that there are times when the Moon can be seen during daylight.

As the Moon completes its journey and approaches new moon again, the Moon is a waning crescent.  The Moon grows thinner and thinner as it gradually disappears in the bright daytime sky, to return again in a few days as a waxing crescent.  And so it goes, month after month, year after year.

Follow-up Questions on Reading 

1. 1. Name the phases of the Moon in order from new to full and back to new again.
   2. Imagine your head is the Earth, your left hand is the Sun, and your right hand is the Moon.  Where would you place your right hand to have a new moon?
   3. Under this same set up, where would your right hand be to represent the location of a full moon?
   4. Position your right “moon” hand above or below your “earth” head.  Is this a good representation of the Moon’s orbit?
   5. Why don’t we have a solar eclipse or a lunar eclipse every month? Hint: Think about what you did in  question number 4.

Reinforcing Hands-On Activities

Modeling I:

For this activity, you will need to create a tactile Moon.  In order to do this, apply a small amount of glue to one end of the stick and insert that end into the styrene/styrofoam (Moon) ball. Next, using the puff paint, apply dots to only one half of the ball (from top to bottom). Allow the puff paint to dry. [An alternate method is to carve a rough surface on the ball.]  (The following is quoted directly from one of Noreen Grice’s activities. The Little Moon Phase Book in Braille is no longer available. For a substitute activity that will need to be made tactile and in Braille, see http://analyzer.depaul.edu/see_project/MoonPhases/MoonPhases.htm)

Begin the activity when the tactile Moon is dry. One student holds the Moon and a second student (the Earth) faces that person. The Earth student puts a hand on the shoulder of the Moon student.  They practice, each person moving to the right, in a circle around an imaginary point between them (as if they were dancing). Eight steps should complete the circle. The Earth student’s hand on the shoulder of the Moon student helps both students move as a unit and remain face to face. 

Once both students are comfortable turning as a unit, the third student (located a few feet away) shakes the jingle bells. This person represents the Sun. The bells provide an audible reference to the direction of the Sun.

The Moon student stands so that his/her back is to the Sun. The Sun student’s ringing bells should be heard in front of the Earth student. The tactile side of the ball represents the illuminated part of the Moon and should face the Sun (not visible to the Earth student). 

The Earth student puts his/her other hand on the Moon (ball). The student touching the Moon should use the palm of the hand to touch one side of the Moon. When the Sun, Moon and Earth are aligned in this way, the Moon is in New Moon Phase.

The Earth student takes one step to the right as the Moon student takes one step to the right. The bells should be heard in front of and to the right of the Earth student. Using the edges of the stick as a reference, the Moon student rotates the stick to the left, halfway to the next side of the stick so that the edge is facing the Moon (student). A small curve of tactile Moon is visible (to the Earth) on the right side of the ball. This is the Waxing Crescent Moon.

The Earth and Moon students each take another step to the right. The bells should be heard to the right of the Earth student. The Moon student rotates the stick to the left until the first side of the stick is reached. About half of the Moon should be visible to the Earth student on the right side. This is the First Quarter Moon.

The Earth and Moon students each take another step to the right. The bells should be heard from behind the right side of the Earth student. The Moon student rotates the stick to the left, to the next edge (more than half of the tactile Moon should be visible from the Earth) on the right side. This is the Waxing Gibbous Moon.

The Earth and Moon students each take another step to the right. The bells should be heard behind the Earth student. The Moon student rotates the stick to the left to reach the second side of the stick. The entire tactile Moon is visible from the Earth. This is the Full Moon.

The Earth and Moon students each take another step to the right. The bells should be heard from behind the left side of the Earth student. The Moon student rotates the stick to the left, halfway to the next side. Some of the tactile Moon has disappeared from the right. This is the Waning Gibbous Moon.

The Earth and Moon students each take another step to the right. The bells should be heard from the left side of the Earth student. The Moon student rotates the stick to the left, to the third side. Only the left half of the tactile Moon should be visible from the Earth. This is the Last Quarter Moon.

The Earth and Moon students each take another step to the right. The bells should be heard from the left front of the Earth student.  The Moon student rotates the stick to the left to the next edge. Only a curve of tactile Moon should be visible on the left edge. This is the Waning Crescent Moon.

The Earth and Moon students each take another step to the right. The bells should again be heard in front of the Earth student. The Moon student rotates the stick to the left, to the final side of the stick. We have returned to the starting point, the New Moon. You have now completed a simulation of the Moon’s phases!

Modeling II

Figure 1.2.1 A three-dimensional model of the Earth and Moon with the dark side hemisphere of the Moon indicated with a rough material. The Sun’s light will be coming from a direction away from this model.

The bells may still be used to indicate the direction of the Sun while students work with the model.  The 8 phases of the Moon are marked on the foam board, and the Moon has a “dark side” indicated by a rougher surface.

Students could work with this to determine the Sun-Earth-Moon angles and confirm the lit portions of the Moon during each phase.

One way to demonstrate the Earth-Moon sizes and distances to scale is to give each student a meter stick, a 3.5 cm ball, and a 1 cm ball.  By holding the 3.5 cm Earth at one end of the meter stick, and the 1 cm moon at the other, one will appreciate that it would take having the Moon only slightly above or below the Earth-Sun line to prevent eclipses.  At this scale, the Sun would be over 390 km (240 mi) away.

Summary and Post-Assessment Questions

1. 1. The phases of the Moon occur because during the course of a month, the Sun, Earth, and Moon are in different positions relative to each other as the Moon orbits the Earth. Use the items in this activity to represent the Sun, Moon, and Earth, and arrange them correctly to represent the relative locations for the phases new moon, first-quarter moon, full moon, and third-quarter moon.
   2. Think about the angles involved, and how much of the lit side of the Moon we see at each phase.  What phase still isn’t clear to you?
   3. Many people have the misconception that the phases of the Moon are caused by the Earth’s shadow falling on the Moon, throughout each month, not just during a lunar eclipse.  Think of an observation that proves this idea wrong and share it with each other.

Relevant Information and Links 

StarChild Question of the Month for November 1998,  http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question3.html  High Energy Astrophysics Science Archive Research Center (HEASARC),, Dr. Alan Smale (Director), Astrophysics Science Division (ASD),t NASA/ GSFC. [Retrieved 01/16/2012]