Lessons from the Moon: Fourth Quarter

Image: Copyright NASA

The moon has been a source of fascination for people through out time. Every culture has stories about it that explain its existence, why it passes through phases, and that tell what might happen to people at different times in its cycle. The term lunatic comes from the belief that during full moons people behave insanely. Luna is the Roman name for the moon goddess.

Before the era of modern science people wanted to understand why the moon passed through phases. To explain things they told stories.

  • The Mayan people, who once lived in the area we call Central America, said that the moon was an old man’s big belly.  As he rolled over and more and more of his big belly faced the sun, the moon got bigger and rounder. Then, a big jaguar would pounce on him and eat his fat belly till there was no more to see. The old man needed three days to rest and grow stronger so that he could grow that big belly again and you would see it growing to full.
  • Mesopotamia has Ishtar who is the daughter of the moon god Sin. When her lover Tammuz died she wanted to find him and so traveled to the underworld.  To do so she was required to shed her clothes. To preserve her modesty Sin darkened the moon face. As she returned from the underworld she was allowed to have her clothes back and so the moon shines brightly again.
  • Can you find other myths to explain why the moon has phases? How is like these? How is it different? Which is your favorite and why?

?????? Can you write a story, from your own experience, that would tell others why the the moon has phases???????

If it is morning where you are, go outside and take a look at the moon.  Here, in the south Tx gulf town where I live, the moon rose at 12:46 in the morning and will set at 1:47 this afternoon.  It is in its third quarter today and will slowly wane until, next Sunday, there is a new moon, rising and setting with the sun.

We have seen, and may have written, stories about why the moon has phases.  Because people were always wondering about the phases, people were always trying to come up with better explanations about why the moon has phases. Scientists know the moon has phases because it circles, revolves, around the earth about once every 29 days. (Can you find out the exact length of time?) As it revolves a different amount of the moon is able to reflect light from the sun.

So, what is going on?

  1. The moon revolves around the earth in a fixed period of time. (See if you can find out how long it takes.)
  2. The moon reflects light from the sun.
  3. The moon always shows the same face to the earth.
  4. As it revolves it changes its position in relation with the earth and the sun.
  5. During the new moon it has its back to the sun and its face to the earth. The moon’s back is getting all the light and reflecting it away from the earth so the face of the moon is hidden in shadow.
  6. As it moves along its orbit, more and  more of its face is looking at the sun in such a way that the earth can “see” the reflected light. This is the waxing moon. (Waxing means growing) When you can see half the face lit by the sun, this is the first quarter. The slivers of moon between new and first quarter are called crescents.
  7. The phase between first quarter and full is a waxing gibbous (gibbous means bulging).
  8. When all the of the moons face is looking at both the earth and the sun we see a full moon.
    • (Advanced concept: because the moons orbit around the earth is at a 5 degree tilt to the earths orbit around the sun we don’t have an eclipse of the moon every month. Can you explain why?)
  9. The orbit continues in reverse, through waning (getting smaller) gibbous, third quarter, waning crescent and then to new moon again.

Here is a demonstration you can do to show what happens.


  1. Two people and a flashlight or one person and a floor lamp without its shade.
  2. A ball about the size of a baseball to a softball.
  3. Tape to mark the directions that you are facing. (optional)
  4. Darkened room


  1. Place the person with the flashlight or the floor lamp in a fixed location. He will not move.
  2. Have the person with the ball stand in a fixed position and hold the ball at eye level and at arm’s length in front of her face. (You can stick a picture of man or rabbit on the ball to represent the side of the moon that is always facing the earth.)
  3. The person with the ball stands facing the sun with the moon held at arms length between their face and the sun. Be careful not to stare straight at the light bulb.
    • What part of the ball is lit?
    • What phase of the moon is this?
  4. Without changing how you are facing the ball, turn 90 degrees to the right.
    • What percent of the ball is lit, relative to how you are looking at the ball.
    • What quarter is this?
    • Is this a waxing moon or a waning moon?
  5. Turn another 90 degrees to the right.
    • How much of the moon facing you is lit?
    • What phase is this?
    • Is there a shadow from your head? What would this be an example of? (lunar eclipse where the earth forms a shadow on the face of the moon. This is uncommon because the moon’s orbit is tilted 5 degrees from the plane of the earth’s orbit.)
  6. Turn another 90 degrees to the right.
    • What phase is this?
    • How much of the moon facing you is lit?
    • Is this waxing or waning?
  7. If you want you can repeat this including the crescent phases by turning 45 degrees each time. (Math Extension)
    • Why do you turn 90 degrees in the first demonstration? How many days does this represent if the moon makes one complete revolution in about 29.5 days?
    • Why do you turn 45 degrees each time in the second demonstration? How many days does this represent?

How close do you think the old stories come to describing what is happing during the phases of the moon? Why do you think this? How close did your story come? Why do you think this?


Moon, earth, phase, crescent, waxing, waning, gibbous, full moon, new moon, revolution (of one object around another), orbit, plane of orbit (older children).

Topics covered:

Science (astronomy), language arts (writing and story telling) mythology, math (angles), critical thinking (explaining reasons).

Resources and credits:

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question3.html (moon phases and image)

http://lunar.arc.nasa.gov/science/phases.htm (moon phases)

http://www.moonphases.info/moon_phases.html (moon phases)

http://www.newhorizons.org/strategies/multicultural/freed.htm (myths about the moon and a version of the activity)

http://www.csmonitor.com/2002/0917/p18s01-hfgn.html (Mayan myth about the moon and the jaguar)

http://www.eternal-moon.org/goddess.html (Myth of Ishtar and others)

I welcome comments on this lesson and any ideas that you think would improve it.

4 comments to Lessons from the Moon: Fourth Quarter

  • Interesting post, having a little trouble accessing the RSS feed. I would quite like to subscribe to your blog. Will try again tomorrow, hopefully it is fixed by then – Otherwise send me an e-mail and I might be able to help. Thanks, the guys from Thai Online Shop oa

  • thenatureschool

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    I usually post on Sundays.

  • I have read few of articles here and can say it was really interesting, thanks for sharing this.