For the theme "lunar cycles," I made a representation of how the lunar cycle matches up with the sun. Specifically, I realized I wasn't clear on what cycle determined whether you could see the moon during the day or night. So, I looked it up! The answer being: at the full moon, it rises at sunset, and rises later each day, until at the new moon it's rising at sunrise. So I tried to capture this:
The gray half-circles indicate when the moon is up, and the yellow/orange represent when the sun is up. The small light blue half-circles are for the high tides. I tried to balance being representational with being abstract enough to be a usable stripe/dot. It came in the bottom half of entries.
I knew there would be a lot of designs that had all the phases laid out in a row like I did, but I stuck with it anyway. My favorite in that vein was this one, plus this one that put them in a circle. Others I liked were the ones that looked like a quilt, sort of Scandinavian, or retro and sketchy.