1. Moon does not emanate light Moon is tidally locked
Moon phase basics
Moon does not emanate light
Moon is tidally locked
Half the moon is always lit
Light comes on the moon from the right hand side

2. Phases of the Moon
The sequential changes in the appearance of the Moon as it revolves around the Earth are called the phases of the Moon.
When the Moon is between the Sun and the Earth we barely see its dark side. This is a new moon.

3. Phases of the Moon
As the moon continues to revolve around the Earth we see varying amounts of Sun on the side facing Earth become larger (waxing).
When the Moon is on the “other” side of the Earth and it is fully lit it is called a full moon.

4. Phases of the Moon
As the Moon continues to move around from the Earth its lit side lessens (waning).
The waning phases look opposite of the waxing phases. (Follow the sun!)
The Moon then returns to its new moon phase and the cycle starts all over again.
Each time this occurs it is called a lunar month. A lunar month is 29.5 days long.

5. The line separating light & dark is called the “terminator.”

6. Phases of the MOON animation
Hyperlink to animation -

7. Why do the phases of the moon occur?
One important thing to notice is that exactly one half of the moon is always illuminated by the sun. Of course that is perfectly logical, but you need to visualize it in order to understand the phases.
At certain times we see both the sunlit portion and the shadowed portion -- and that creates the various moon phase shapes we are all familiar with.
COMMON MISCONCEPTION: MOON PHASES ARE CAUSED BY THE SHADOWS OF EARTH ON THE MOON. NOT TRUE! So the basic explanation is that the lunar phases are created by changing angles (relative positions) of the earth, the moon and the sun, as the moon orbits the earth.
Also note that the shadowed part of the moon is invisible to the naked eye; in the diagram above, it is only shown for clarification purposes.
Have students identify how many degrees there are in a sphere. (360)
Have students identify how much of the moon is lit at all times (50%, half the moon)
Since we have the potential to see up to half the moon (the entire side we see at full moon) the maximum we can see is 180 degrees.
Now look at the waxing crescent. It’s at a 45 degree angle to our line of sight. Since we could see 180 degrees and the moon is at a 45 degree angle it only looks like 25% of the moon is lit. (45/180=0.25)
First quarter is at a 90 degree angle. Since we could see 180 degrees and the moon is at a 90 degree angle it only looks like 50% of the moon is lit. (90/180=0.50)
Waxing gibbous is at a 135 degree angle. Since we could see 180 degrees and the moon is at a 135 degree angle it only looks like 75% of the moon is lit. (135/180=0.75)
Full moon is at 180 degree angle. Since we could see 180 degrees and the moon is at a 180 degree angle it looks like 100% of the moon is lit (of the side we can see) (180/180=1.00)
Waning Gibbous, Third Quarter and Waning Crescent are exactly like the Waxing phases. However, since the moon is around the other side of the Earth your field of view is reversed so the shadow is on the other side.
Light always come on from the right side of the moon during waxing phases then shadow comes on from the right side of the moon during waning phases.
Why do we see the moon in phases?
The moon does not give off its own light but reflects sunlight.
The moon is tidally locked, so we always see the same half of the moon from Earth.
Half the moon is always lit by the sun.
However, as the moon revolves around the Earth, we see various portions of the side facing Earth as sunlight reflects off of that side at different angles.
Since we can only see the sun-lit portions of the moon (not portions in shadow), the moon appears to change shape as it revolves around the Earth. These different shapes are called “phases.”
Sometimes no sunlight is being reflected off of the side of the moon facing Earth and sometimes all of the side facing Earth is reflecting sunlight with varying amounts in between.

8. Create a Flip Book
Use the paper supplied to create a “Phases of the Moon” flip book.
Draw each phase of the moon in the order they occur and correctly label each one.
Stage Name (Waxing/Waning) Phase name, line of sight angle out of 180o, % we see lit
At the end, describe why the moon has phases.
Summary at the end:
Have students identify how many degrees there are in a sphere. (360)
Have students identify how much of the moon is lit at all times (50%, half the moon)
Since we have the potential to see up to half the moon (the entire side we see at full moon) the maximum we can see is 180 degrees.
Now look at the waxing crescent. It’s at a 45 degree angle to our line of sight. Since we could see 180 degrees and the moon is at a 45 degree angle it only looks like 25% of the moon is lit. (45/180=0.25)
First quarter is at a 90 degree angle. Since we could see 180 degrees and the moon is at a 90 degree angle it only looks like 50% of the moon is lit. (90/180=0.50)
Waxing gibbous is at a 135 degree angle. Since we could see 180 degrees and the moon is at a 135 degree angle it only looks like 75% of the moon is lit. (135/180=0.75)
Full moon is at 180 degree angle. Since we could see 180 degrees and the moon is at a 180 degree angle it looks like 100% of the moon is lit (of the side we can see) (180/180=1.00)
Waning Gibbous, Third Quarter and Waning Crescent are exactly like the Waxing phases. However, since the moon is around the other side of the Earth your field of view is reversed so the shadow is on the other side.
Light always come on from the right side of the moon during waxing phases then shadow comes on from the right side of the moon during waning phases.
Why do we see the moon in phases?
The moon does not give off its own light but reflects sunlight.
The moon is tidally locked, so we always see the same half of the moon from Earth.
Half the moon is always lit by the sun.
However, as the moon revolves around the Earth, we see various portions of the side facing Earth as sunlight reflects off of that side at different angles.
Since we can only see the sun-lit portions of the moon (not portions in shadow), the moon appears to change shape as it revolves around the Earth. These different shapes are called “phases.”
Sometimes no sunlight is being reflected off of the side of the moon facing Earth and sometimes all of the side facing Earth is reflecting sunlight with varying amounts in between.