The Earth and he Moon form an inseparable couple. Under the effect of a fundamental force called gravity, the Earth attracts the Moon, but the Moon also attracts the Earth. This attraction of the two celestial bodies makes the Moon to make effect mainly in the oceans. This is what provokes the tides, which are one of the effects of the Moon that we will see in this article.
The Moon and the tides
Two times per day, the level of the sea goes up and down. This movement of the water is what we call the tide. This phenomenon is provoked by the Moon due to the attraction that she exerts on the Earth, mostly on the oceans. Near the coast, when the Moon is in the opposite side of the Earth, the water goes down, making the descend of the sea level and leaving the coast exposed. This happens when it’s low tide. Then, when the Moon passes another time, the water goes up another time, due to the attraction effect that the Moon exerts, and falls another time onto the coast, this makes the sea level go up.
For strange as it may seem, there are also earth tides. Without knowing it, the earth down our feet goes up between 30 and 40 cm and then descends another time! This type of tide is also caused by the effects of the Moon, like I’ve already said before, due to the gravitational attraction onto the Earth.
The alternation between the high tides and low tides is due because the Earth turns on its axis in 24 hours, for this reason the Moon is never on the same place.
The big tides
The sun also exerts an attraction on the Earth, although it’s lower than the Moon’s. When the three celestial bodies are aligned in the named new Moon, as in the full Moon, represented in the two top parts of the image, the attraction of the Moon and the Sun are added, making that during that period of time the tides are stronger.
In the contrary, when the Sun and the Moon don’t “stretch out” in the same direction, represented in the two down parts of the image, the tides are weaker.
An incredible effect
The constant attraction of the Moon, which make go up and down the level of the oceans as the level of the earth, makes our planet to turn each time slower on his axis. This deceleration of the spin of the Earth on its axis provokes a widening of the days (900 millions of years ago the days only lasted for about 18h), and a continuing distancing of the Moon respect to the Earth of 3,8 cm per year.