The Ocean’s Pulse: Mastering the Tidal Cycle

If the Moon's gravity pulls ocean water into a bulge and the Earth's rotation brings a beach into that bulge, then the water level at that beach will rise to a high tide.

If there are two water bulges on opposite sides of the Earth and the Earth rotates once per day, then most locations will pass through both bulges, creating two high and two low tides.

If the water bulges stay aligned with the Moon while the Earth rotates underneath them, then the rotation is the reason we experience a changing tidal cycle every few hours.

If a cycle describes the repeating rise and fall of water, then high and low tides along with the movement of water between them are parts of that cycle; however, volcanoes are not part of a tidal cycle.

If the Moon and Sun exert a gravitational pull on the Earth's liquid oceans, then that pull creates the bulges. If the bulges exist because of gravity, then gravity is the driver of the cycle.

If the Moon's gravity pulls the water more than the Earth on the near side, a bulge forms. If the Moon pulls the Earth more than the water on the far side, a second bulge is left behind, creating a balanced tidal cycle.

If the water level rises and falls in a predictable pattern that starts over every day, then the entire sequence of events is a tidal cycle.

If the Earth rotates once every 24 hours but the Moon moves slightly ahead in its orbit, then it takes an extra 50 minutes for a point on Earth to realign with the Moon to finish the tidal cycle.

If "diurnal" means daily and the prefix "semi-" means half, then a semidiurnal cycle is one where the pattern repeats twice a day. If a beach sees two equal high and low tides, it is a semidiurnal tidal cycle.

If water must move around landmasses and through channels, then the shape and depth of the coast change the water's path. If the Moon's phase changes the pull strength, then it also affects the tidal cycle.

If the water level rises and falls over several hours, then the peak of that rise is the high-water mark. If this peak happens during the daily cycle, then it is part of the tidal cycle.

If the Earth is spinning while the Moon is moving, then the Earth must spin a bit more than 360 degrees to catch up. If this "catching up" defines the daily tidal cycle, then it is called a lunar day.

If the Moon's gravity pulls water into bulges at two points, then water must be pulled away from the areas in between. If you are in one of those "in-between" areas, then you are at the low point of the tidal cycle.

If the movement of the Earth and Moon follows stable, mathematical orbits, then their positions can be calculated far into the future. If we know their positions, then we can predict the resulting tidal cycle.

If the Sun and Moon line up or if the Moon gets closer, the gravitational pull increases. If a storm pushes extra water, the height changes; however, the time of day and the Moon's color do not affect the tidal cycle.

If the water is moving toward the shore and filling up the beach during the tidal cycle, then it is "flooding" the area. This is known as a flood tide.

If the tide must change direction from coming in to going out, then there must be a brief moment of stillness at the peak or trough. If the water is temporarily still during the tidal cycle, it is called slack water.

If a full lunar day is 24 hours and 50 minutes and contains two high tides, then dividing that time in half shows that each half of the tidal cycle lasts about 12 hours and 25 minutes.

If the water level moves up and down during the tidal cycle, then there is a strip of land that is sometimes wet and sometimes dry. If this area is between the tides, it is the intertidal zone.

If the water is transitioning from a high state to a low state, then it must flow back out to sea. If the water is flowing out, then this part of the tidal cycle is called the ebb tide.