The Tidal Force Vector

First created: Thu Apr 6 2000
Last update: Fri Apr 7 2000

Tidal Vector Calculator

Tidal force vector calculator. It can display the effects of the Moon and Sun separately or combined.

The dates and times used by the calulator are consistently UTC. Look for the maximum solar vertical pull around noon local time. This maximum is always accompanied by a minimum in the Nort-South component and a zero in the East-West component. Similarly, using the altitude calculator, verify that when the Moon peaks locally this calculator shows a maximum lunar vertical pull.

for new jersey:

To get local time in NJ, subtract 5 hours from UTC in the winter, 4 in the summer. Noon local time will then be 17:00 or 16:00 UTC.

Special Cases

Try to generate the following plots.

A 3 day plot will show the evolution of the tidal force components. Note how the Z (vertical) component is never negative and is at a minimum when the Moon rises or sets (explain!).

A 28 day plot will show the 14 day periodic effect clearly.

A 90 day plot will have ... nice colors!


I haven't yet cross checked the tidal vector against another independent source. Use this data at your own risk!

The vertical tidal forces are not the ones causing sea tides. The sea is already balanced vertically and is not compressible. I is the horizontal tidal forces that shift the water around.

There is a constant force perpendicular to the axis of the Earth, due the Earth's 24 hour rotation (centrifugal force). It is lattitude dependent, but is not time dependent, so the experiment will not notice it and I ignore it here.

The Earth rotates every 28 days around the center of mass of the Earth-Moon system (still situated with in the Earth). This effect has a much longer period (14 days) than the 12 hour period of the tidal vector, and I'll ignore it for now. I'm not even sure this effect exists independently of the tidal signal ...


tidalvector.cpp. Source code for the calculator.