Lunar Cycle Basics and The Magic of FENS

Confession: When I took my certification exam for teaching I failed the lunar cycle section. I do not remember ever learning the lunar cycle in school and, other than knowing the the full moon is bright, I never really felt the need to learn more about our nearest neighbor. Not that I don’t love space, I just never really named the lunar phases. But, our students need to learn that, if only to be informed citizens of a world that might someday no longer be entirely Earth bound.

The lunar cycle is also, of course, in both the state and national standards:

TEKS 8.7B demonstrate and predict the sequence of events in the lunar cycle

Next Generation Science Standards:

MS ESS1-1 Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons.

The lunar cycle is pretty tough for students (and adults), so today we’ll just tackle one part – learning the names and position of the various phases of the moon.

I have a few projects I like to do to make the moon more “real world,” so at this point the students would (hopefully) already be interested and have developed a “need to know” for the lunar phases. In other words, this should probably not be lesson 1 of a series unless doing a review. There is not really a “hook” or “explore” section, mostly direct teach, but sometimes that is what it is. Fortunately, there are some hands-on fun things the kiddos can play with.

Materials (per group)

  • ball painted half black and half white (to represent moon)
  • ball painted half black and half blue (to represent Earth)
  • lunar phase model template
  • large window
  • 2 plastic bottle caps (used as supports to keep the Earth and moon from rolling off the table)
Earth moon sun template
This is a picture of the template used

Have students gather the materials and orient the template on their table so that all groups have the “sun” side of the template facing towards a large sunny window. The light itself doesn’t actually matter, we’re just trying to hammer home the idea that the sun is MUCH BIGGER than the Earth and moon.

Ask students to place the “Earth” ball (half blue and half black) on the template where they think it should go. Hopefully, all students put the Earth on the place labeled “Earth” with the blue side facing the “Sun.” Remind students that the side of the Earth facing the Sun is experiencing “day” while the other side is experiencing “night.” The rotation of the Earth causes day and night (that’s another lesson!).

We start by placing the “Moon” ball at position 1. The white side of the ball should be facing directly toward the Sun/window so that the setup looks like this:

I tell the students that they are in an alien space ship [insert appropriate sound effects] high above the Earth looking down from space. We see that the Earth and moon are both half lit by the sun. [NOTE: for some reason, at this point in culture “lit” is a term that makes students giggle. Who knows.]

Next I have students crouch down as if they were on the Earth, not above in space anymore. I’ve fount it works best to tell students to stand at position 1 and look directly over/through the Earth. What do they see?

Students expect to see all bright because they are looking at the Sun. But, the part of the moon that they see is all dark! What lunar phase is this? Well, I’m glad you asked, because students can refer to the handy guide on their notes page and record the appropriate name and image.

Now we move the moon in its orbit around the Earth to position #2. VERY IMPORTANT. The white part of the moon sphere must remain pointed straight out at the window/big Sun. Students want to turn and angle their little moon to point toward the little Sun, but that will disrupt the model. Make sure students have their models aligned as shown below:

So, again, we travel in the alien space ship [sound effects] to look down from space and see that both the Earth and the moon are still half lit. The amount of light that the moon is receiving from the sun is NOT changing. But, if we go back to the Earth and look from the Earth perspective, now crouching down at position 6 and looking directly across, we see something different.

Now students should see a tiny portion of the white part of the moon visible on the right side of the model. When they look back at their notes page, they can then match that visual with the label “waxing crescent.”

I explain to the students that “waxing” is the term we use for when the moon is getting brighter from our perspective here on Earth. You can remember “waxing” means brighter because (1) if you wax your car or the floor it gets shinier (2) if you wax your legs or arms to remove the hair your arms or legs look shinier (3) candles are made of wax and candles are shiny. Whatever helps the term stick in their head. We call the shape a “crescent” because it is (1) like a crescent on the Islamic symbol (2) like a crescent roll or croissant that they might eat.

Next, the moon moves to position #3. Again, we travel in our alien spaceship and see that both the moon and the Earth are half lit by the sun. Point out the amount of light the moon receives is NOT changing! One common misconception about the lunar cycle is that the moon looks different to us because it is receiving a different amount of light from the sun. Nope! The moon is always half lit. What we here on Earth can see changes.

So we take the Earth perspective again and have students look from position #7 across to the moon at position #3, as shown below.

From the “Earth” perspective, students should see a view that looks like this:

First Quarter

This is the first quarter moon. Two points to make (1) From our perspective, it looks like we see half the moon (half a shaded circle). Remind students that the moon is a sphere and has two sides. We see a quarter of the moon (from our perspective), that is why this is a first quarter moon. (2) There are 4 quarters in a dollar, there are 4 quarters in the lunar cycle AND there are 4 weeks in a month. It takes approximately 1 week to move from the first quarter moon to the full moon. Students need to know the length of the lunar cycle to accomplish the objective “predict phases” and this is a good point in which to introduce that piece of information.

Moving on….we take the lunar model and transition the little moon, still with the lit side facing toward the sun, to position #4 and, again, look from both the space perspective on top and the Earth perspective (viewing across from position #8).

From the “Earth” perspective, students should view the moon model and observe this:

Time for more vocabulary! Here, we are still “waxing” because the moon still can appear brighter to us. The shape is now called a “gibbous” moon. This phase is the “waxing gibbous.”

Gibbous is such a random term! I try to help the students remember by saying that it is like “give us!” because it is like a fat little moon that has been asking to be “given” more and more. Some of my students pointed out to me that there is a character on the TV Show iCarly (which my negative 57 Pop Culture IQ was not aware of) named Gibby who has a little bit of a belly that looks a little like the gibbous shape:

Apparently, the word “gibbous” comes from a root meaning “hump-backed” so if that tidbit helps, feel free to use it.

Now we move on to everyone’s favorite phase: the full moon! The moon model moves to position #5 and we observe from position #1:

We see that when the moon is in this position, the moon appears fully lit by the sun. But remember! From the space perspective the moon is always half lit.

At this point the students usually catch on to the process and can finish the other half of the lunar cycle diagram on their own. You just need to point out that the moon is now starting to appear less bright, so it is no longer called “waxing.” Instead, when the moon is getting less bright, transitioning from full moon to new moon, we say that the moon is “waning.”

To help students remember “waning” I tell them about how my little sister couldn’t say the letter “r” when she was young so, if the sky was getting darker, she would ask if it was about to “wane” (instead of rain). Waning = getting less bright.

Once students have completed and filled in the entire diagram you can introduce the final key components to lunar cycle (test question) success. First, a rhyme. How do you remember if the moon is waxing (getting brighter) or waning (getting less bright) just when looking at a picture?

When the light is on the right, then the moon is getting bright.

So if the illuminated portion as seen from Earth is on the right side of the picture, the phase a “waxing” phase. On the left, the phase is a “waning phase.”

Second, the magic word “FENS” What?! FENS! FENS stands for “full moon,” “Earth,” “new moon,” “Sun.” When students get a lunar cycle diagram on a test question I tell them to first label the Earth with a big “E” and the Sun with a big “S”

Then, if you fill in the letters to make “FENS”, you automatically label the locations of the full moon and new moon! No chance for error.

What if the Sun is shown on the opposite side? The procedure still works. You just write FENS backwards (SNEF):

Now students have all the knowledge and skills they (theoretically) need to accomplish the learning objective. Practice, practice practice!

I included one STAAR question on the notes page for guided practice as a class.

I like this question because it reinforces the timing of the lunar cycle – approximately 2 weeks between full and new moon – which is something that often gets lost in the lunar cycle lesson.

Here is another practice activity I made for my students. The slides show them a picture of the Earth, moon, and Sun and the students need to draw the view of the Moon as seen from space and from Earth.

There are also some good practice games online for the lunar cycle. Unfortunately, many use Flash, which does not make my students’ Chromebooks happy, but here is one very simple version of a matching game that at least gives some vocab practice. Have fun!

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