Earth's Tides
As the Moon orbits the Earth the sea water below heaps up and slowly shifts
in the direction created by the Moon's gravitational force. See the
dynamic display below of the Sun, Earth and Moon. On average the high
tide appears at any particular place on Earth about 50 minutes later each
day because each 24 hours the Moon moves 13.2 degrees in its orbit from
west to east, making moonrise about 50 minutes later. The time
between high tides is always about 12 hours and 25 minutes or half the
time from one moonrise to the next.
The high point of the tide is not underneath the Moon but lacks behind
it due to the inertia of the water running up-hill against the gravity pull
of the Earth's field.
- Spring Tides: At full and new moon,the Sun and Moon are aligned, the
tidal forces of the Sun is added to that of the Moon's,
causing high Spring tides.
- Neap Tides: When the Moon is at half-moons, Sun and Moon at right angles,
the Sun and Moon forces are oposed, causing low Neap tides.
Earth's Tides Assuming shallow,uniform water shell.
The line in the above display represents the Greenwich Meridian symbolizing
one complete rotation of the earth on its axis in 24 hours or one
Apparent Solar Day.
The moon completes one orbit of the Earth in approximately 29.5 days or
one synodic month. A synodic month is the
time in days measured from one new moon to the next new moon as observed
from the Earth. The Moon's sidereal month takes 27 days, 7 hours, and
43 minutes since it is measured with respect to the stars.
- Diurnal inequality:
- Land Tides:
- Atmospheric Tides:
- Tide effect created by the Earth's geography:
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