Hi there, middle school science teacher here. We’re studying the Earth/Sun/Moon system and I’m about to teach tides. In the past, I have always taught that tides are highest at the full and new moons, because the Sun and the moon are aligned.
However, this year I decided to add a graphing activity using real-world data for tides from the month of September, and comparing it to the moon phase each day. I’m looking at the numbers and according to the data, the highest tide is actually happening 3 days after the full moon, and 2 days after the new moon.
What’s going on? Is there a reason for the delay (that 6th graders can understand)? Have I been teaching it wrong all these years?
The guts of the explanation of lag is that the moon and sun don’t cause water heights directly. They cause water FLOW.
The height is the result after the flows are summed up.
lag in tides is always a problem for everyone looking at tides.
eg when up river, when on the west coast of continents, when the there’s a small waterway next to a large one.
Because its quite complicated , and the complications vary depending on location, its too much to touch on… its a topic which never ends .
If we lived on Waterworld, then it’d work like those nice simple diagrams you see in textbooks. But our planet has a bunch of inconvenient continents that prevent the water from flowing everywhere that it wants to, and so it sloshes and piles up. If you lived in the middle of the Pacific, far from any land worth mentioning, it’d align much better.