The above GIF shows the changing tides in a unique manner, by splicing together pictures taken throughout an entire day, at 20 minute intervals! The resulting effect is that it looks as if time is spiraling around the image. You can also see both pairs of high and low tides, one set during the day and one set during the night.
Unless you’ve lived by or frequently visited shores, you’ve probably never had to think about the tides much. Sure, the concept of tides is fairly well known by many, but how much of a difference does it make?
Well, as the video shows, quite a lot! Before I had watched time-lapses of tidal behavior, I had assumed that the water level difference between high tide and low tide wasn’t more than a meter or so. The reality is that in some places, like at Hall’s Harbour in Nova Scotia, Canada, the difference can be up to 14 meters! The rate at which it rises is about 2.5 centimeters a minute, escapable unless you were wading far out at sea.
After realizing how much more water is present in one area at high tide, I got to thinking. Where does all the water go when it recedes? Surely it can’t just… disappear? Then, I realized that at any one point in time on Earth, if it is high tide somewhere, then it is low tide elsewhere. So, the water is pulled towards those continuously moving (at least, relative to the surface of the Earth) points at which high tide exists, and thus, low tide exists.
Thankfully, there aren’t mystical forces drinking the ocean up away from shores, or we’d have bigger problems to deal with.
Another thing about tides that I didn’t know about until just a few days ago was that yes, the moon causes tides, but in what way? It turns out that tides are caused by the magnitude of the difference in gravitational force felt on opposite sides of a body, not necessarily the magnitude of the forces themselves. I had always accepted that the Moon’s gravitational force somehow caused tides since that’s what I was told since I was very young, but I also figured that the gravitational force on the Earth from the Sun must be stronger than the Moon’s, or we’d probably crash into the Moon. I had never put two and two together, and wondered why it was the Moon that caused much larger tides, even though the Sun pulls the Earth with much greater force.
The secret is that gravitational force drops proportionally to the square of the distance from the object, so the difference between gravitational force felt at two points separated by a constant distance is higher when they are closer to the massive object than if they were farther away. In this case, the two points are opposite sides of Earth, and the objects causing a force to be felt are the Moon and the Sun.
It was thanks to a recent Astronomy homework assignment that it was made apparent to me! See, you really do learn things in school. 😂 I’m looking forward to the next astronomical epiphany, but until then, enjoy this spiraling tidal time-lapse! 🌊