Going back a bit further, billions of years ago, if we could go back in time, the moon we see would be much larger than it is today.
The Unique Role of the Moon
Going back billions of years, besides being much larger than what you see now, the moon had a constant influence on Earth.
During that time, Earth was spinning very fast. Around 370 million years ago, a year had about 400 days, and a day lasted 21 hours. About 1.3 billion years ago, a day was only 16 hours long, and the faster Earth spun, the shorter the days became. Earth spun rapidly, with fierce winds and tumultuous seas, making conditions on our planet harsh.
Although the formation of the moon remains a mystery to this day, life on Earth couldn’t even exist without it. Fortunately, the moon exists, and in the early days, when most of the Earth was covered by ocean, the moon’s gravitational pull influenced the tides. It raised the ocean’s waters and pulled them in the opposite direction, from east to west, creating a significant resistance force. This resistance force caused Earth to slow down its rotation by 0.00000002 seconds.
Even now, the moon is still performing its role.
Earth’s Slowing Rotation and the Moon Moving Away
Why was the moon so large in the past and now it’s so small? We now have an answer. As Earth’s rotation slows down, it exerts an opposite force on the moon, increasing the moon’s rotational speed. As a result, the moon gradually moves away from Earth.
The distance has been accurately measured, thanks to the Apollo missions that landed on the moon’s surface decades ago. To measure the distance between Earth and the moon, scientists used laser beams and calculated the time it took for the light to return. The calculations showed that the moon is moving away from Earth at a rate of about 3.8 centimeters per year.
The gradually increasing counterforce is causing Earth’s rotation to slow down to the point where we now have a day of nearly 24 hours. At this point, humans emerged on Earth, and the visible size of the moon also became approximately the same as the sun.
The Fading Total Solar Eclipse
The view of the moon near the planet Earth in space.
Everyone can witness a total solar eclipse once or twice in their lifetime. This astronomical phenomenon can only be observed when humans exist because when the moon is the same apparent size as the sun, you can experience this spectacular celestial event.
As the moon moves between the sun and Earth, all three align in a straight line, creating a total solar eclipse. As the moon continues to move farther away, it will gradually become smaller until it can no longer completely block the sun.
Scientists have calculated that in about 600 million years, the moon will no longer be able to completely block the sun, and at that time, the phenomenon of a total solar eclipse will no longer be visible on Earth.