Moon Phases and Tides

The moon dominates our night sky, and the changing phase of the moon is one of the most striking changes we see from night to night. But there are other changes that are so small that you probably have never noticed them before. Watch the video Understanding Moon Phases to see them illustrated in Stellarium.
Read 4.5 Phases and Motions of the Moon to learn how the Moon’s phases result from its changing illumination by the Sun.
Watch the teacher video Moon Phases for a helpful summary of what you have read. If you like, you can experiment with the interactive Lunar Phases Simulator for yourself.
You’ve probably been learning about moon phases since grade school. Our goal in this lesson is to take our understanding a step further so that we can actually predict the moon’s phase based on the time of day and the moon’s location in the sky. The secret is to draw a picture. Watch the video Moon Phase Drawings to see how I approach solving these kinds of moon phase questions.
If you’re having trouble relating the moon phase to the time of day, here’s one way to think about it… The time of day is essentially just the position of the sun in the sky. If it is straight overhead, then it must be noon. If it is setting, it must be close to 6 pm. The phase of the moon is determined by how far the moon is from the sun in our sky. If the moon is right next to the sun, you will have a “New Moon.” If it is on the opposite side of the sky, you will have a “Full Moon.” So if you know the phase, then you can know how far the moon is from the sun. And if you also know where the Moon is, then you can figure out where the sun must be. And if you know where the sun is, then you know (roughly) what time it is.
It’s kind of like saying … “If Jack and Jill are 20 feet apart” (this is like the moon phase) “and Jill is 5 feet from the tree” (this is like telling us where the moon is in the sky) “then Jack must be 25 feet from the tree.” (this is like telling us what time it is because it tells us where the sun is in the sky).
(Optional) Movies and games often get science concepts wrong. I recently noticed this to be especially true while I was playing Fortnite with my son. They didn’t even get the basics about the moon’s motion correct. Watch Five Ways Fortnite Gets Astronomy Wrong to see what I mean.
Explore 4.6 Ocean Tides and the Moon to understand how the Moon’s gravitational pull creates ocean tides and the role of Earth’s rotation in experiencing these tides.
(Optional) Google has created several interactive “Google Doodles” that include a card game based on the phases of the moon. If you want to test your knowledge of moon phases and have a little fun, then check out Rise of the Half Moon.