地球自轉的原因

科學家們認為，一顆巨大的物體，也許是火星的大小，影響年輕的地球，挖出了一大塊最終成為我們月球的物質。 這種碰撞使地球以更快的速度旋轉。科學家估計，地球早期的一天只有大約6個小時。

Scientists think that a large object, perhaps the size of Mars, impacted our young planet, knocking out (挖出了) a chunk of (大塊) material that eventually became our Moon. This collision set Earth spinning at a faster rate. Scientists estimate that a day in the life of early Earth was only about 6 hours long.

月球剛形成時，與地球的距離較今天接近。隨著地球的旋轉，月球的引力讓海洋上升和下降。潮汐和轉動的地球之間存在一點摩擦，導致旋轉減慢一點。隨著地球的減速，讓月球以極慢速度遠離地球。

The Moon formed much closer to Earth than it is today. As Earth rotates, the Moon's gravity causes the oceans to seem to rise and fall. There is a little bit of friction between the tides and the turning Earth, causing the rotation to slow down just a little. As Earth slows, it lets the Moon creep (緩慢行進) away.

月球和地球的距離正逐步拉遠。我們可以使用極其精確的原子鐘精確測量旋轉減速的程度。一百年後，一天將比今天長約2毫秒。

The Moon is drifting (漂流) farther from Earth. We can use extremely accurate atomic clocks to measure exactly how much the rotation is slowing down. One hundred years from now, a day will be about 2 milliseconds longer than today.

https://spaceplace.nasa.gov/review/dr-marc-earth/earth-rotation.html