Through the course of time, mankind’s interest with what lies beyond our universe has lead to an interest in our closest celestial neighbor, the moon. Countless times, movies have used the moon for romantic appeal and an untold amount of folklore. Our interest, is such that we spent millions of dollars developing technology to go to the moon, as we saw occur on July 20, 1969, when Neil Armstrong and Buzz Aldrin took man’s first step on the planet.

A whale is seen as a full Hunter’s moon rises in Puerto Madryn, Argentina, Sunday, Oct. 9, 2022. (AP Photo/Maxi Jonas)

In the late 16th Century, man’s questions about our world and what lies beyond, lead to theories from two famous astronomers Nicolaus Copernicus and Galileo, regarding the center of the universe and what orbit our planet and others seem to follow. Born nearly a decade after Copernicus, Galileo developed the hypothesis that the sun was the center of our universe around which the earth and other planets revolve, a theory that was challenged by the Catholic Church. Eventually accepted through scientific proof, the work that Copernicus and Galileo accomplished, paved the way for further exploration of our cosmos. In our current day, the technology that transmits information back to the scientific community about distant stars and / or planets, light years away, continues to improve; yet it is our focus on the moon that has captivated us the most. Seen on a daily basis, the moon’s effects on our tides usually goes unnoticed; however, there are times when the exception rather than the rule takes shape and astronomically high tides wreck havoc to communities that lie by their rising waters

By definition, the word tide is the alternate rising and falling of the surface of the ocean, as opposed to current which is the horizontal or sideways flow of water. A day’s high and low tide cycle is effected by the moon and the sun, both playing a part in the gravitational pull and causing fluctuation of water on the earth’s surface, but because the sun is 93 million miles away, it has much less of a gravitational impact on earth, compared to the moon, which is ONLY 240,000 miles away. So how does the moon effect our tides? That answer comes from the scientific knowledge that the moon and earth in actually, revolve together around their common center of mass. The two astronomical bodies are held together by gravitational attraction, but kept simultaneously apart by an equal and opposite force, called centrifugal force. Known as a “fictitious” force, it is only present in an accelerated object moving through a curve and not in an object that moves in a straight line at a constant speed.

At the earth’s surface, an imbalance between the gravitational force and centrifugal force results in a tide-producing force which pulls toward the moon, in the earth’s hemisphere facing the moon. On the opposite side of the earth, the tide-producing force is in the direction away from the moon. Simply put, our planet has an elongated or egg shaped look to it’s surface. Imagine, for example, a magnet (the moon) passing over a coin (earth), time and time again. The magnet would not be close enough to catch the coin, but instead makes the edge of the coin, or in this case water, rise a few centimeters. This tidal bulge that occurs is a direct result of the moon revolution around the earth and is called a “Lunar Tide”.

Photo Credit: NOAA

Twice a day, lunar tides effect the world’s waters by having two high tides and two low tides, but it is the moon’s various phases that gives us three specific types of tides. When the moon is FULL or NEW, the gravitational pull of the moon is the greatest. At these times, the high tides are very high and the low tides are very low. This is what is known as “Spring Tide”. They occur when the earth, moon and sun are in line with one another and the gravitational forces are at their maximum. The opposite of “Spring Tide” is “Neap Tide” and occurs when the moon and sun are at right angles to one another, with respect to the earth, causing the bulging of the earth’s waters to cancel each other out. This result is a smaller difference in high and low tides. The last type of tide is rare, is called the “Proxigean Spring Tide”, and occurs when the moon is closest to the earth. During the last several hundred years, there have been less than 50 instances when this type of tide has occurred, but when they do occur in conjunction with strong storms, the greatest loss of life has occurred. One such example was on September 8, 1900 in Galveston, Texas, when around 6,000 people perished due to the combination of New Moon phase, high tide and the approach of a very powerful hurricane. As previously stated, tides occur four times a day, approximately every six hours. The difference between the high and low tides is called the range of tide and can simply be calculated by taking the difference between the tides. For example, if the water depth at high tide was 10 feet and at low tide 5 feet, the range of tide is 5 feet.

The most pronounced range of tides occur at the Bay of Fundy, where twice a day about 100 billion tons of water move in and out of this inlet. The Bay of Fundy’s topography, along with a particular weather phenomenon, called a Tidal Bore, is the reason that a tidal range of 50 feet can be seen! A Tidal Bore is the leading edge of a rising tide and can be thought of as the crest of a wave that is forced up the mouth of rivers and streams by the narrowing landscape. Since tides tend to slow due to friction when they reach shallower water, water tends to pile up and a Tidal Bore is formed. It is no wonder that the Bay of Fundy makes the list of nature’s twelve natural wonders.

Looking through a telescope at the Celestron booth during the International CES Friday, Jan. 9, 2015, in Las Vegas. (AP Photo/John Locher)

So how important is tide information and who uses it? Knowing tide heights and times in conjunction with moon phases is useful information for fishermen, engineers etc. and has application to navigation through intercoastal waterways and underwater demolition. The source for obtaining tide information, earth orientation and moon phases come from the U.S. Naval Observatory locally in D.C. Established in 1830, its primary objective was to care for the Navy’s charts and navigational equipment, but now is the preeminent authority in the areas of precision time and astronomical data required for accurate navigation and fundamental astronomy.