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About
Tides:
The moon is the major cause of the tides. The
“lunar day” is 24 hours and 50 minutes, most places have two high tides and
two low each day. This clock hand
rotates once every 12 hours and 25 minutes (twice each lunar day). Your tide
clock stays in exact step with the moon. But
there are many other factors that can make the day-to-day tides a little earlier
or later than the tide clock shows. The
sun also affects the tides but has less than half the influence of the moon.
When the sun and moon are lined up as they are at the time of a new moon
and full moon, their influence combine and high tide is higher and the low tide
is lower than normal. When the sun and moon are at right angles as they are in
the first quarter and the last quarter of the moon, the sun cancels some of the
moon’s effect and the range is smaller than normal. Also, at these times the
sun will make the tides somewhat earlier or later than average. This is why it
is so important to first set your clock on the day of a full moon, as the moon
has the dominating effect with the tides.
Starting
your clock:
Obtain the local Tide Table and a calendar which shows the days for the
full moon, new moon etc. On the day
of the full moon set the hand at high tide precisely at the time of high tide
according to the local tables. If
the clock is set correctly on the day of the full moon it will display the
minimum variance through the month. Usually
the discrepancy will be less than 30 minutes and therefore will be unnoticeable.
Typically, only four or five days each month will have a difference as great as
an hour.
Other
Information:
There are actually two tidal cycles: a twice-daily cycle and a once
cycle. On a tide when the two cycles help each other, high tides will be higher
and low tides lower. On the next tide, when they conflict, the tidal range will
be smaller. The relative strength of these two cycles varies from week to week,
and also varies from one place to another. The United States, along the Atlantic
coast the two tides have a similar range, but on the northern Pacific Coast
there tends to be a large difference between the two tides. Further south and in the Gulf of Mexico, the difference is so
great there often appears to be just one high tide and one low tide per day.
Abnormal atmospheric pressure can temporarily affect the time and height
of tides. A difference of one inch in barometric pressure will cause about one
foot difference in sea level. Strong on-shore winds will change the times of low
& high tides as well.
To order a tide clock go to the Accessory section of the shopping
center.
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