The tides vary depending on the Moon mainly because of the Moon's gravitational attraction on Earth. This attraction creates high and low tides due to the difference in gravitational force on different parts of the Earth.
The lunar gravity pulls the water from the oceans towards it, creating a bulge of water on the side of the Earth facing the Moon. Surprisingly, a second bulge appears on the opposite side, due to the difference in gravitational force felt between the near side and the far side of the Moon. These two bulges are the origin of high tides, while areas located at 90° experience low tides at the same time. Throughout the day, with Earth's rotation, each region goes through two cycles of high and low tides. That's why, even if we don't always see the Moon in the sky, its influence on the oceans is constantly felt.
The lunar phases indicate how the Earth, the Sun, and the Moon are positioned relative to each other, and this has a direct influence on the amplitude of the tides. When the Sun, Earth, and Moon are aligned— which happens during the full moon or the new moon—the gravitational forces add up. The result: higher tides called spring tides. Conversely, when the Moon is at a right angle to the Sun-Earth axis, during the first or last quarter phases, the forces partially counterbalance each other. As a result, we get lower tides, called neap tides. These differences in amplitude explain why beaches can be very wide on certain days, while at other times they seem to almost disappear with high tide.
The distance between the Earth and the Moon is constantly changing, as the lunar orbit is not circular but slightly elliptical. When the Moon is at its closest point, it is referred to as perigee. At this time, its gravitational pull on the oceans is strengthened: the result is stronger tides called perigean tides. Conversely, when it is farther away — a position called apogee — its influence decreases and the tides are significantly less pronounced. This is why, from one week to the next, the difference between high and low tides can vary greatly. Similarly, the position of the Moon relative to the Earth's equator also plays a role: depending on whether it is higher or lower in the sky, it pulls differently on the oceans, further influencing the height and intensity of the tides.
Tides do not come only from the Moon, because the Sun also plays its role. Even though it is very far away, its enormous mass still allows it to exert a significant pull on the oceans. When the Earth, the Moon, and the Sun are aligned (that is, during the full moon or new moon), their forces combine. The result: this creates spring tides, with high amplitudes. Conversely, when the Sun and the Moon form a right angle as viewed from the Earth (during the first and last quarters of the moon), their forces interfere with each other. This creates neap tides, which are smaller and less spectacular. In short, their interplay explains the variations in tidal amplitudes throughout the month.
Depending on the regions of the globe, tides are not at all the same. The shape of the coasts, the depth of the seabed, and even the size of an ocean strongly influence the amplitude of the tides. A clear example is the Baie du Mont-Saint-Michel, particularly famous for its giant tides, precisely because of its very unique geography (funnel shape). In other regions, such as the Mediterranean, one observes hardly visible tides, mainly because this sea is almost enclosed and too small to fully experience the lunar effects. Even on a local scale, you can see significant differences due to the layout of the coastline, reefs, or river mouths that enhance or hinder the rise of the waters.
The tidal phenomenon gradually slows down the rotation of the Earth, resulting in the imperceptible lengthening of our days. Hundreds of millions of years ago, a day on Earth lasted only about 20 hours!
The Moon does not always move away from the Earth at the same distance: its elliptical orbit slightly varies the intensity of the tides depending on the time of the month, sometimes resulting in exceptionally high or low tides.
Although it is much less massive than the Moon, the Sun also exerts a significant influence on the tides: when the Moon, Earth, and Sun are aligned (during new or full moon), their combined effects generate particularly pronounced spring tides.
Even though water is most often associated with tides, the Moon exerts its gravitational pull on the entire Earth. That is why there are also land tides: our continents move a few centimeters daily due to the lunar effect!
Sure! Here’s the translation: Yes, the Moon does not orbit the Earth in a perfect circle but in an elliptical orbit. Consequently, when it comes closer to the Earth (at perigee), its gravitational pull is stronger, thus generating higher tides. Conversely, at the farthest point (apogee), the attraction is weaker, reducing the amplitude of the tides.
During full moons and new moons, the Sun, Earth, and Moon are aligned (a phenomenon known as syzygy). This configuration amplifies the combined gravitational force of the Moon and the Sun on the oceans, resulting in higher tides known as spring tides.
Yes, the lunar gravitational force also causes "land tides," where the Earth's crust lifts very slightly, by just a few centimeters. Even the atmosphere experiences a slight tide due to the lunar gravitational pull, but these phenomena are still much less noticeable compared to ocean tides.
The amplitude of the tides strongly depends on the geography of the coasts, the underwater topography, and the water depth. For example, in narrow bays or estuaries, tides are amplified, while they remain weak in open and deep areas like certain parts of the Pacific.
The Earth rotates on its axis in 24 hours, but since the Moon also moves slightly each day in its orbit, it takes about 24 hours and 50 minutes for a specific point on Earth to return to the same lunar position. This generally creates two high tides and two low tides each day, shifted by approximately 50 minutes each day.
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