Tides are influenced by the Moon and the Sun due to the gravitational force they exert on Earth. The Moon, because of its proximity, has a greater influence than the Sun on tides.
Gravity is the attraction exerted between two bodies. The Earth, the Moon, and the Sun mutually attract each other, but not all with the same intensity: the Moon, although small compared to the Sun, influences us more because it is much closer. This gravitational attraction pulls on the oceans on the side of the Moon, causing the water level to rise in that area. But not only that: on the other side of the planet, opposite the Moon, the water also rises because it is less attracted than the Earth, which is in the middle—it's as if the ocean is slightly left "behind." The Sun, although more massive but much farther away, also plays its part and reinforces or weakens this lunar attraction depending on its position. These combined forces create our famous tides.
The tidal force comes from the difference in gravitational attraction exerted by a celestial body on different regions of the Earth. Why this difference? Simply because the side of our planet closest to the Moon is more strongly attracted by its gravity than the opposite, more distant side. This disparity causes a kind of stretching, slightly deforming the Earth and creating two bulges of water: one on the Moon side and one on the opposite side. The result: two high tides per day, spaced about twelve hours apart. The Sun, although much more massive, is also very far away, so its tidal force is weaker (about half that of the Moon). Nevertheless, it is not negligible and contributes to the phenomenon. This combined action explains why sometimes the tides are particularly strong or, on the contrary, quite weak.
The position of the Moon and the Sun relative to the Earth directly affects the intensity of the tides. When the three celestial bodies (Earth, Moon, and Sun) are nearly aligned, their gravitational forces combine, which is called spring tides, particularly strong. Conversely, when the Moon forms a right angle with the Earth and the Sun, their forces partially oppose each other, resulting in neap tides, which are significantly less pronounced. This is why, depending on the phase of the lunar month, we regularly observe more or less pronounced variations in the ocean water level.
Spring tides occur when the Sun, Earth, and Moon are almost aligned. In this position, the gravitational forces combine and create particularly strong tides, with very high water levels at high tide and very low levels at low tide. Conversely, we refer to neap tides when the Sun and Moon form a right angle relative to the Earth. As a result, the forces partially cancel each other out, and the tides are much less pronounced, with smaller differences between high and low tide. These cycles alternate approximately every two weeks according to the lunar phases.
The Bay of Fundy in Canada holds the world record for tidal height, with an amplitude that can reach up to 16 meters, roughly equivalent to a 5-story building!
Even though the Sun is much more massive than the Moon, the Moon's influence on Earth's tides is stronger due to its relative proximity to the Earth.
On Earth, each lunar day lasts about 24 hours and 50 minutes, which explains why the daily tide schedules shift by approximately 50 minutes each day.
Tides do not occur solely in the oceans: the gravitational pull of the Moon and the Sun also causes slight deformations in the Earth's crust, known as land tides, and even in the atmosphere, referred to as atmospheric tides.
Tides strongly influence coastal biodiversity by regulating intertidal habitats that are alternately exposed to air and submerged under water. This alternation defines specific biological and ecological patterns. Many species have thus adapted to this daily rhythm, such as certain crustaceans, mollusks, and migratory birds whose feeding depends on tidal cycles. Tides also play a crucial role in the circulation of nutrients and the oxygenation of coastal waters, promoting diverse marine life.
Yes! Tidal forces are not limited to our planet. For example, the effects of the lunar tide caused by Jupiter on its moon Io are so strong that they lead to significant volcanic activity. Although tides on other planets may manifest differently than those we know (for instance, in the form of rock deformations instead of the movement of large bodies of water), the physical phenomenon related to gravitational attraction and the differences in gravity across various parts of celestial bodies is universal.
Although the Sun is indeed much more massive than the Moon, it is also much farther from the Earth; gravitational force depends on both mass and distance. In the case of the Moon, its proximity greatly compensates for its significantly lower mass: its gravitational effect, particularly its gradient (the difference in attraction between the parts of the Earth that are close and those that are far away), is therefore more pronounced than that of the Sun, making its effect more decisive on tides.
Tide coefficients are numbers that express the expected tidal amplitude compared to a defined average value. The higher the coefficient, the greater the difference between low tide and high tide will be. These coefficients are used to forecast the intensity of tides, thereby facilitating maritime activities such as fishing, navigation, and coastal safety based on the expected conditions.
The Earth rotates on its axis in about 24 hours, while the bulges formed by tidal forces due to the Moon remain properly aligned with it. Thus, during the course of one rotation of the Earth, each point successively finds itself under two water bulges (causing high tides) and two troughs (low tides), which explains why most places generally experience two high tides and two low tides each day.
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