Monday, October 05, 2009

A tide timing puzzle

An odd thing just occurred to me. We entered Inchon harbor this morning at about 7 and left this evening at about 6, in other words, pretty close to sunrise and sunset. The moon was full, so it was very close to the horizon in both cases. So why was there a high tide? The way I was always taught about tides would seem to predict a low tide under those circumstances.

3 comments:

Loz said...

The moon rises and sets. High tide will be at it's highest point. Even if that is low in the sky. A bit of playing around with http://www.fourmilab.ch/cgi-bin/Yoursky showed the highest point around 6:30. http://www.mobilegeographics.com:81/locations/2755.html confirmed this was when the high tide was.

When the moon doesn't go particularly high above the horizon is when you'll get the least difference between high and low tides (ignoring the effect of the sun).

Ron said...

> High tide will be at it's highest point

Yeah, you'd think.

> the highest point around 6:30

No, that can't be right. The moon was full yesterday. A full moon is always near the horizon at 6PM local time.

Loz said...

I was getting my local times and universal times mixed up. Sorry about that.

The Wikipedia article you linked is full of interesting stuff that seems to explain it though. Specifically http://en.wikipedia.org/wiki/Tide#Bathymetry

Always nice to learn something new.