the old moon and the sea
rising moon and rising tide, watch the invisible force of the moon!
| Date: | 21./22.8.2008 | Time: | 18:39 to 20:13 UT (next day), 40s interval |
|---|---|---|---|
| Exposure: | 2313 x up to 30s | Field: | 180o diagonal |
| Camera: | Nikon D3 | Optics: | f=10.5mm at 1/3.2 |
| Place: | Eagle Island, Maine, USA | Observer: | Till Credner |
The time lapse covers about 25 hours by the seashore of Maine, USA. Watch the tide coming and going! Especially after night falls, you can see the rising moon and then, quite simultaneously, the rising ocean with the ascending moon. No wonder, our moon is the main cause of the tides! In the simple newtonian gravity model of the tides, the high tides are in the direction of the moon and on the opposite side of the earth. The low tides are in a right angle to the moon. This is what we expect and can see here. High tide occurs when the moon is high in the sky (observer at point C in the graphics below) and low below the horizon (observer at A). Low tide is when the moon rises (B) and sets at the horizon (D).
Simple Newtonian gravity model of the lunar tides for an observer on the equator:
However, as usual this image is far too simple. Our earth has continents and is not completely covered by the ocean. Therefore the high tide can't turn around the earth freely as earth rotates, the land stops the way of the water. Instead, the water of each ocean is swashing back and forth like in a bath tub. Or it goes in circles in each ocean basin like in a glass of wine. And in reality many more aspects like the sun, tidal friction, moons declination and local weather effects play an important role for the ocean tides. Therefore on most locations by the seashore, the time of high tide is far off of the culmination of the moon (point C). The location in Maine however fits more or less well with the simplest tidal model. Moon and ocean are rising simultaneously, connected by the invisible force of gravity.
Since the moon was already in the waning phase, I call the video, with kudos to Ernest Hemingway: "The old Moon and the Sea".
5 times accelerated video with repetition:
- Get the HD version from VIMEO
- Compare three of the images
- Wikipedia on the tides