Make a Moon Phase Diagram With Cookies

By Dr. Daniel Barth

When we first look up at the sky, the Moon is probably the first thing we notice. It fascinates us, child and adult alike, with its changing phases, the markings on its surface, and the way it seems to change size as it moves from horizon to zenith. If you are lucky enough to own a telescope, the Moon was probably one of the first things you looked at, and it still draws the gaze of professional and amateur astronomers alike every cloudless night world wide.

But the Moon puzzles as much as it fascinates; once we start noticing the changing phases of the Moon, we cannot help but ask, “How does it do that!” As an astronomy teacher, this is one of the first, and most persistent questions that my students asked of me. Textbooks and websites try to explain the phases of the Moon with diagrams and drawings, but these left almost every student (and parent) unsatisfied. The best way I found to understand the way the Moon works is to make a model of it.

Let’s start with something fun — and delicious. You will need seven chocolate sandwich cookies (I like Oreos!), and a plastic knife. Begin by “unscrewing” the first cookie – one half is a dark circle, this will be your New Moon; the other half is a white circle, this will be your Full Moon.

Unscrew your next cookie and use the plastic knife to cut a crescent shape into the cookie filling, and carefully scrape away the larger portion of filling. The thin white crescent of filling represents your Crescent Moon – make two of these shapes.

For your next two cookies, use the plastic knife to cut the filling exactly in half, scraping the unneeded portion of the filling away as before. These represent your First and Third Quarter Moon.

For the last two cookies, use the plastic knife to cut a crescent , just as you did before; but this time, scrape away the smaller crescent leaving the majority of the filling behind. These represent the Gibbous Moon.

Now that you have all of your “Moons” ready, place them on a sheet of paper or a plate in the order shown in the diagram to the right..

Label the phases you’ve created, starting with New, at the 12 o’clock position, then moving clockwise, label Crescent, Quarter, Gibbous, Full, Gibbous, Quarter and Crescent. If you have a cell phone with a camera on it, take a picture of your diagram so you can use it to refer to when you are out observing the Moon.

You can label the right half of your diagram waxing (evening), and the left half of your diagram waning (morning). The waxing Moon is in the process of getting larger each night, leading up to the full moon phase – this phase is best seen in the early evening just after sunset, an ideal time to use your telescope or binoculars. The waning Moon is in the process of getting smaller each night, leading up to the new moon phase, when there is no moon visible in the sky at all. The waning Moon is best seen in the early morning, just before or after sunrise when the sky is still a bit dark. If you get up early for work or school, this is an ideal time to try and catch a glimpse of the waning Moon.

Now that you have your Moon Phase diagram, you can use it to predict what will happen next to the Moon in your night sky. You can save your diagram on a plate covered with a piece of plastic wrap, or if you’ve taken a photo of your diagram – you can enjoy your “Moon Cookies” right away. Remember to share them with your classmates or siblings – Mom & Dad may enjoy one, too.

Once you have spotted the Moon in the night sky, what phase does it most resemble? Try drawing the phase yourself – an easy way to do this is to trace around a coin or jar lid on a piece of paper with a pencil, and then shade in the part of the circle that represents the dark portion of the Moon’s disk as you observe it. Make a lunar observation sheet and record the date and time of your observation after you finish.

Although you may want to go outside and watch the Moon every night as I often do, keep in mind that each phase we’ve labeled lasts 3-4 days. For the Moon to go from New to Quarter phase takes about a week, and the entire lunar cycle takes almost a month, a little more than 28 days. We call this complete cycle of lunar phases a Lunation. With your cookie phase diagram, you will understand the Moon better, and have fun watching the changing of the lunar phases in the night sky.

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Dr. Daniel Barth left a career as a research scientist to teach; he has spent more than 30 years teaching astronomy, physics and chemistry at the high school and college level. A successful science fiction writer, Barth is the author of Maurice on the Moon, Doomed Colony of Mars and other works. He is currently Assistant Professor of STEM Education at the University of Arkansas in Fayetteville, and author of the Astronomy for Educators program.

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