? The Moon is moving further and further away from the Earth, with what consequences
"They say that the Moon is moving away from the Earth, of course we still have a lot of time before that has a real impact, but all the same, what will be the consequences on Earth?" , asks a reader on our Facebook page.
The Moon, located just over 380,000 kilometers from Earth, is gradually moving away from us, at a rate of 3.82 centimeters per year.
"They say that the Moon is moving away from the Earth, of course we still have a lot of time before this has a real impact, but what will be the consequences on Earth?" , asks Ghislain Hoyeau on the Sciences et Avenir Facebook page . Each week, we select one reader question to which we provide an answer. Thank you for your insatiable curiosity.
Indeed, the Moon, located just over 380,000 kilometers from the Earth, is gradually moving away from us, at a rate of 3.82 centimeters per year. This progressive distancing has long been known to astronomers and is caused by the Earth's tides which exert such a gravitational force on the Moon that they accelerate its movement, slowly expelling it from the Earth's sphere of influence. At the same time, the exchange of energy between the Earth and its satellite slows down the speed of rotation of our planet. This double phenomenon of the Moon moving away and the Earth slowing down means that... the days are getting longer.
Days get longer by about 1.8 milliseconds every century
Indeed, the days lengthen each century by approximately 1.8 milliseconds: in 3.3 million years, the day will therefore last 24 hours and... one minute! Conversely, in the past, the Moon was closer and the Earth rotated a little faster.
However, the approach of the Moon was not linear and it is very difficult to estimate its distance one or two billion years ago. By analyzing rocks almost 1.5 billion years old, which bear the traces of past climatic alternations, the American professor of geosciences Stephen Meyers calculated that 1.4 billion years ago, the Moon was closer to Earth - 340,000 kilometers away - and the days were 18.68 hours long ! Results that must be compared with those obtained by other purely astronomical methods to be validated.
Another consequence linked to the distance of the Moon: total solar eclipses will become rare , so much so that it will no longer be possible, in the fortunately distant future, to observe a total eclipse of the Sun.
No more total solar eclipses
The phenomenon of total solar eclipses is a transitory episode in the history of our planet. Since the astronauts of the Apollo missions placed reflectors on the Moon, we can precisely measure the time traveled by a laser beam, reflected on these reflectors and deduce the Earth-Moon distance to within 7 centimeters (and this is how we discovered that our satellite is moving away from us today).
In short, the Earth-Moon couple was only 22,500 kilometers apart, 4.5 billion years ago. At that time, our satellite was so big in the sky that it totally hid the solar disk when it came between it and the Earth.
We are therefore currently exactly in this "magic window" where the two disks have almost the same apparent size. But it won't last. “In 620 million years, more or less long periods will follow one another (a few million years) with and without total eclipses , underlined Pascal Descamps, astronomer at the IMCCE (Institute of Celestial Mechanics and Ephemeris Calculation) in a previous article in Sciences et Avenir . This is due to the variation in the eccentricity of the Earth's orbit. During periods when this eccentricity will be zero - the Earth's orbit drawing a perfect circle - then total eclipses will occur despite the retreat of the Moon. Assuming a constant speed of removal of the Moon equal to 3.8 cm / year, the complete disappearance occurring in 1.21 billion years, when the distance between the two planets will be 402.346 kilometers .
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