“Bye Bye Moon” is not meant to be a sequel to Goodnight MoonDid you know that the moon’s distance from Earth varies each month? I didn’t know that until this week, even though I know a lot about our Moon and I write about it at least once a month here.

Our Moon has a rather eccentric orbit and it is moving away from us at about one and a half inches per year. Scientists attribute this to tidal friction with the Earth’s oceans which also slows down how fast the Earth rotates, This lengthens our day by about 1 second every 40000 years.

Okay, it is not something we really will notice or need to worry about, but because scientists can do simulations, they can figure out that four and a half billion years ago when the moon was being formed,  it was only about 15,000 miles from Earth. Now, it is about 238, 831 miles from Earth.

Back then, an Earth day might have been only 5 or 6 hours long and there would be 1400 days in one year. More recently, at least relatively, around 900 million years ago there would be 480 days of about 18 hours each in one Earth year. That would certainly give us a very different lifestyle.

And projecting into the future, we would expect longer days but fewer of them in a year.

Even though we can’t observe these changes within a lifetime, it awesome and full of wonder to me that these changes are happening.

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