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In the lush garden of Woolsthorpe Manor in Lincolnshire, England, grows a lone apple tree. This is not just any old apple tree but the very tree where it is said that, in the summer of 1666, Isaac Newton watched an apple fall and was inspired to develop his theory of gravity as an invisible force that pulls everything toward the Earth.

It's a wonderful story, but is it just a legend, or is there some truth to it? Newton himself communicated this discovery to several acquaintances, including the French philosopher and writer Voltaire. And, quite frankly, I believe it. After all, here's a guy who invented calculus, an entire field of advanced mathematics, just so he could understand the movements of the moon and planets.

And then he turned 26!

Yeah, the guy was a genius, no question about it, and many folks consider him to be the most brilliant scientist who ever lived. But when you see the waxing gibbous moon hanging above us this week, you may think he was mistaken. I mean, if Newton was right about gravity, shouldn't the moon fall to Earth?

The answer, it turns out, is rather simple – so simple that it took a genius like Newton to figure it out. The moon is falling to Earth, but since it's also moving on its own, it never hits the ground.

Confused? No need to be. Newton explained it clearly with a wonderful analogy in his famous three-volume work titled "Philosophae Naturalis Principia Mathematica," more commonly known as the "Principia."

Imagine a cannon, for example, on a high mountain. Fire the cannon and the cannonball will eventually fall to the ground. Fire it faster and the projectile will go farther but will still eventually hit the ground. No surprise there.

But what if you fired the projectile so fast that, as it falls, the Earth curves away from it at the same rate? It would never hit the ground but would continue to circle the globe. In other words, it would be in orbit.

Newton's principles of gravitation help us understand the motions of everything from baseballs to rockets to planets. Now, it's true that in the early 20th century, Albert Einstein, another stunningly brilliant scientist, devised a more refined explanation of gravitation in which he describes it not as an attractive force but as a warping of space that causes bodies to move as they do. But Newton's laws still hold for everything we see in our everyday world, including the moon.

That the moon is moving on its own is why it never falls to Earth. If you don't believe it, go outside and check for yourself this week.

Since the moon completes one orbit around our planet every month, that means that it should change its position eastward against the more distant stars by about 12 or 13 degrees each night.

Notice where the moon appears and which stars are nearby, and on the next night at around the same time, check it out again. Thanks to Isaac Newton, you won't need an apple tree or calculus to discover why the moon doesn't come crashing down!

Visit Dennis Mammana at dennismammana.com.