Moon, Sun, Tides and Everything

 

 

 

Didn’we have a beautiful Red Moon last Wednesday! I got a bit crazy about it and forgot about everything else. Then I thought that such a perfect Sun-Earth-Moon alignment must have made one hell of a tide.

The main causes of tides are lunar attraction (by far the biggest one) and solar attraction. The Moon pulls up the oceans so it creates a kind of bulge in its direction. This bulge occurs once every lunar day (24 hours and 50 minutes).

On the opposite side of the Moon there is another bulge called the antipodal bulge. This happens because the Moon attracts the Earth solid mass more than it does the ocean. This explains why in most places you get every lunar day a sublunar high tide, then another high tide half a lunar day (12 hours 25 minutes) later. So far so good.

Things are not that simple because the Sun does about the same thing but on a smaller scale and on a 24 hours cycle. So we get bigger tides when the Sun and the Moon are aligned (full moon and new moon situations) and smaller tides when they are at 90 degrees from each other (quarter).

The time interval between consecutive high tides (12 hours 50 minutes) is only an approximation. While it works reasonably well in mid-ocean locations it gets very complicated on shorelines (where it matters most, Murphy’s law) due to the coast shape, local bathymetry, winds and atmospheric pressure.

Give me space physics any day, it’s easier!

References:

https://en.wikipedia.org/wiki/Tide

Picture: https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/13-7-tidal-forces/