I am intrigued by tidal waters. Tidal flow has a remarkable predictability and, at one and the same time, a high degree of irregularity. The movement of the fluids of the earth are affected by a number of factors. If we focus only on the oceans for a while we can make a case for the rise and fall of these waters that is largely affected by gravitational forces exerted by the Moon, the Sun, and the rotation of the Earth; and by the three-dimensional shape of the basins in which the water resides. Of these influences, the most influential would be the moon.
The moon exerts a tremendous gravitational force upon the whole planet. Its effects are felt by the earth's crust, which rises and falls a few millimetres with the passing of the moon overhead, and the earth's atmosphere which rises and falls many metres via the same influence. The moon also affects our bodies as they are unconsciously pulled toward the moon adding to and reducing our weight, pulling body fluids such as blood and amniotic fluids in the same direction as tidal waters. It is no coincidence that an average for women's menstrual cycles is 28 days (varying greatly from woman to woman) while the period of the moon's orbit is 27.3 days and a complete cycle of the moon's phases takes 29.5 days. There is not sufficient space in this article to explain the ways in which these last two numbers are measured. Perhaps a later blog will delve deeper into the movement of the moon around our planet. Indeed I may one day reward faithful readers with the answer to a physics question posed several months ago.
But all of that is an aside to the point at hand: the moon also tugs at the oceans of our world. If you have never done it, I strongly encourage you to spend some time at a tidal portion of the ocean and pay attention to the rise and fall of sea level. If you can, track the position of the moon while watching such things as currents in the water, depths of the water, and the movement of anchored boats in a harbour. Many people have lived beside the sea for years without taking the time to observe the tide. Some are not even aware that water levels rise and fall with a regular rhythm.
In many locations, including False Creek, the portion of sea by which I live, water levels rise to a high tide approximately twice a day, and sink to a low tide approximately twice a day. It is important to say "approximately" because the other factors associated with tides have their effect and contribute to what looks like irregularity in this system. The combined effect of the gravitational pull of the sun and the moon is one of the other factors contributing to our ability to accurately predict sea levels at any given place in the world. Here is a tide chart for Vancouver tidal waters. Tide charts such as this are a good general predictor but even they will not completely reflect sea levels at a specific beach or point along that beach. Tide charts always come with warnings.
I can't help but reflect upon the wisdom of a Creator who designed the planets, moon, and stars in such perfect equilibrium. The gravitational effect of the moon is substantial enough to move the seas, yet small enough to leave the crust of the earth intact even after many centuries of tug and turn. In some places waves rush upon the shore and crash to great effect. In other places the ripples of water are gentle and leave the seashore less eroded. What a wonderful, rugged, changeable planet and universe we have. My heart will praise the God who formed it all with his great creativity.