Long ago but not too far away, Moon was a marble spinning much faster than it does today.
Earth tugged on Moon with all its might until rocky bulges formed on one side.
Now Moon was no longer a marble, but more like a football or lemon.
The bulges were like a bicycle break on Moon, slowing its spin down.
Time went on and on and on and on until one day Moon’s day took the same amount of time as its year.
Did you know Moon has a day and a year?
A day is one rotation and a year is one orbit. Now, they are both 27.3 Earth days long.
This is different from Earth’s moon day, also known as Monday, which lasts 24 hours.
Moon’s bulgy side, its face, now looks at Earth all the time.
Moon’s far side is like the back of its head. One half of Moon’s head is always lit by the sun, but Earth can’t always see that side.
Since it’s sometimes lit up, it’s called the far side, not the dark side, and that’s why scientists never listen to Pink Floyd.
Moon’s face is always gazing down on Earth, which makes Earth happy.
Scientists cannot yet measure the difference between desire and gravity.
Famously yet mysteriously, Moon tugs on Earth, too, and moves the seas around.
The tides are also like bicycle breaks, and every century, an Earth day grows by 2.3 milliseconds.
Many years from now, but not too far away, Earth might become tidally locked to Moon.
Moon would only see one face of Earth, and only half of Earth would ever see Moon.
Does Moon have a favorite face of Earth?
The next time Moon shows up, look up, in case it’s yours.