The phenomenon of the tides is influenced by the Moon and the Sun due to their gravitational attraction on the Earth's water masses, causing regular high and low tides.
Gravitational force is simply the attraction experienced by two objects that have a mass. The greater the mass of an object, the stronger its attraction. Conversely, the greater the distance between two objects, the weaker this attractive force becomes. This gravity is universal: it explains why an apple falls to the ground but also why the Earth orbits the Sun or the Moon orbits the Earth. In our case — the tides — gravity essentially comes from two celestial bodies: the Moon and the Sun. These two pull on our planet and move the ocean water in their own way.
The Moon attracts the water of the oceans towards it by gravitational force, thus creating a bulge of water on the surface of the Earth facing it. On the opposite side, another water bulge forms due to inertia: the Earth is also attracted by the Moon, slightly pulling away from the water located there. This results in two simultaneous marine bulges, one under the Moon and the other directly opposite. As the Earth rotates on its axis in 24 hours, each location passes through these two bulges once a day, generally creating two high tides and two low tides daily. The concrete effect varies according to geographical position, ocean depth, and coast configuration.
Even though the Moon plays the main role in tides, the Sun also gives a serious boost. Since it is much farther away, its gravitational pull on the oceans is about half as strong as that of the Moon. But given its gigantic size, it is impossible for it to go completely unnoticed.
Depending on the position of the Sun relative to the Earth and the Moon, it can either strengthen or weaken the tides created by our natural satellite. When all these celestial bodies align more or less well, the forces add up, resulting in higher tides, known as spring tides. Conversely, when they are positioned more or less at a right angle, their effects counteract each other, leading to lower tides, called neap tides. The Sun thus acts as a sort of supporting actor that increases or decreases the overall intensity of the spectacle.
When the Moon and the Sun align with the Earth, their gravitational forces combine to create more intense tides: this is called spring tides. Essentially, during the full moon and new moon, high tides are higher, and low tides are lower, because the Earth experiences a strong "combined" attraction. Conversely, when the Sun and Moon are positioned at right angles (first quarter and last quarter of the Moon), they counteract each other's effects, and we observe tides with much lower amplitudes: neap tides. They are significantly less impressive. This interplay of attraction between the Sun, Moon, and Earth largely explains why tides vary so much from day to day!
Tides function like a true natural clock with well-known cycles. The most obvious rhythm is that of the daily tides, which occur approximately every 12 hours and 25 minutes. But that's not all: tides also follow a monthly rhythm, aligned with the phases of the Moon (spring/neap tides), as well as an annual cycle influenced by the relative position of the Earth and Sun. Certain times of the year have much more impressive tides. Moreover, over a longer term, there are even variations caused by phenomena such as the tilt of the lunar orbit or the elliptical position of the Moon and the Sun relative to the Earth. All of this results in amplitudes that change constantly—sometimes spectacularly, often subtly.
Even though the Moon is smaller than the Sun, its influence on the tides is about twice as significant due to its proximity to the Earth.
Tides play a key role in marine biodiversity by facilitating the transport of nutrients, thereby creating rich and varied ecosystems, particularly in coastal areas such as mudflats and mangroves.
The Moon is gradually drifting away from the Earth by about 3.8 cm each year. Although it is a minuscule distance, this slow separation subtly affects the Earth's tides over the long term.
On a lunar day (about 24 hours and 50 minutes), there are usually two high tides and two low tides along the Atlantic coasts, while on some oceanic coasts or in closed basins, this rhythm can vary significantly.
The spring tides occur when the Earth, the Moon, and the Sun are aligned, during the full moon or new moon, resulting in a greater amplitude. Conversely, the neap tides happen when the Moon and the Sun form a right angle as viewed from the Earth, thereby reducing the amplitude of the tides.
Yes, the coastal relief can significantly alter the amplitude of tides by constricting or widening the movements of water. Some areas, such as the Bay of Mont Saint-Michel, exhibit very high amplitudes, while other places experience smaller variations.
The Moon is the main actor in tides because it is much closer to the Earth. However, the Sun, although far away, also exerts a notable influence on the phenomenon. When the Sun, Earth, and Moon are aligned, the combined gravitational pull causes exceptional tides known as spring tides.
Yes, thanks to very detailed calculations using astronomical and topographical data, tide predictions are highly accurate. The times and amplitudes of the tides can thus be forecasted well in advance, which is useful for maritime navigation and coastal activities.
The Earth rotates on its axis in about 24 hours. During this rotation, each region experiences two high tides and two low tides, caused by the gravitational pull of the Moon, which creates two ocean bulges opposite each other across the globe.
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