|
Properly
set, our tide
clocks are quite accurate almost anywhere in the world.
However, the effects of the sun, as well as local weather
conditions can cause the tides to vary, sometimes by as
much as 1 1/2 hours during the course of the month. While
there are always two high and two low tides per day, in
some locations, such as the China Sea and parts of the Gulf
of Mexico, the second high and low tides are so small that
there appears to be only one high and low tide per day.
Starting
Your Clock
Obtain a local tide table and a calendar that shows the
days of the full moon, new moon, etc. Many newspapers publish
this information, often near the weather report. On the
day of a full moon, insert your battery precisely at the
time of high tide according to your local tide tables. If
your Tide Clock is set correctly on the day of the full
moon, it will display the minimum error throughout the entire
month. Usually the discrepancy will be less than 30 minutes
and therefore unnoticeable. Typically, only four or five
days each month will have a difference as great as an hour.
|
To
make the best of your Massachusetts Bay Trading Company
Tide
Clock you should understand a little about what causes
the high and low tides. The moon is the major cause of the
tides. The lunar day, the time it takes for the moon to
reappear at the same place in the sky, is 24 hours and 50
minutes. Most locations have two distinct high tides and
two low tides each day. Therefore, the hand on our tide
clocks rotates once every 12 hours and 25 minute, twice
each lunar day. The Tide Clock will always stay 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. It is impossible for us to determine
these conditions for your locality. The sun also affects
the tides, but has less than half the influence of the moon.
When the sun, moon and earth are lined up, as they are at
time of the new moon and full moon, their influences combine
and high tide is higher than normal and low tide is lower
than normal. When the sun and the moon are at right angles,
as they are at the first quarter and last quarter of the
moon, the sun cancels some of the moon's effect and the
range of tide is smaller than normal. At these times the
sun will cause the tides to be somewhat earlier or later
than average. This is why it is so important to first set
your Tide Clock on the day of a full moon, as the moon has
the dominating effect on the tides.
|
|
|
More
information about tides
There are actually two tidal cycles: a twice-daily cycle
and a once-daily 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.
In the United Stares, along the Atlantic Coast the two daily
tides have a similar range, but on the northern Pacific
Coast there tends to be a large difference between the two
daily tides. Farther 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 also cause a temporary increase in sea level.
Both of these effects will change the times of low and high
tides as well. Tides in the lower portions of rivers will
be affected by the changing volume of the river flow.
During
the 29 1/2 day synodic period (the time between new moons)
the moon will have made exactly one less revolution around
the earth. So that there will be exactly two less tides
during that period of time. Therefore, the tidal period
(time between high tides) will equal
29
1/2 days/(28 1/2 days x 2) tides = .5175 days = 12 hr. 25 1/4
minutes between tides.
Note: The crystal frequency in our tide clock is 31.658
kHz which makes one revolution of the lunar clock equal
to a lunar day of 12 hours and 25.24 minutes or 1.03506
times longer than the solar day.
If the tide movement is set at a new or full moon high tide
then the greatest error of up to 1 1/2 hours can occur about
3 to 4 days before or after neap (1/2 moon) or spring (full
or new moon) tides, and the greatest accuracy is at new,
1/2, and full moons. The inaccuracies are not in the movement
itself, but rather are due to the assumptions on which the
tide movement is based. The assumption is that only the
moon controls the tides. Although the moon has a dominating
effect on the tides, the sun also has an effect (46% that
of the moon) and the elliptical orbit of the moon around
the earth can change the tides by +/- 20%. To a lesser extent,
the elliptical orbit of the earth around the sun has a similar
effect. All of these factors not only affect the magnitude
of the tides, but they also affect the timing.
Feel free to email us for an even more
detailed explanation of our tide clock
accuracy at info@massbaytrading.com.
|
|
Pure
Yankee Ingenuity
|
|
