During the last half of the 20th century, now and again I had the opportunity to take a motorboat ride or a ride on a little sailboat out into the Gulf of Mexico. Many times, we happened to see this narrow ribbon of debris floating parallel to the coast some distance out. It looked like foam and bits of human litter riding a wave poised between rolling in one direction or the other. Our dad told us that this line marked the tide, as it either approached the shore or was moving out again.
This ribbon is a visible marker of the turning point of the tides. As the earth spins one full rotation each calendar day, the pattern of the sun's and moon's gravitational pulls on earth shifts. There are high tides and low tides each day, daily patterns.
The biggest high tides come when the sun and moon are in alignment on one side of earth. That occurs at new moon. The lowest tides come when the sun and moon are most separate in the sky from the perspective of the earth. At full moon, the moon rises as sun sets - they are tugging at earth from opposite directions. These are monthly shifts in the tides.
The gravity of the sun and moon as the earth rotates on its (invisible) 'spindle' affects the wax and wane of seas and lakes. The tides thus are also a significant factor in weather fluctuations. The rhythm of life and the activities of many species on the planet are intermeshed with tidal activity. The tides could metaphorically be described as the breathing pattern of the earth.