While gazing up at Earth’s nearest celestial neighbor, the moon, it’s easy to imagine that it’s just a stone’s throw away, but is it really that close?
Because it’s so easy to see the detail of the moon with little to no magnification, I always assumed it was really close to Earth, but after some quick looking into, I discovered that it’s actually not very close at all. In fact, depending on where it is in its orbit, the average distance of the moon from Earth is about 238,900 miles, or almost a quarter of a million miles away!
Understanding a quarter of a million miles
To the average person, it’s probably fairly difficult to really comprehend how far a quarter of a million miles is, but by doing some simple calculations based on a few pieces of information we already know about the moon and Earth, we can begin to better understand and visualize just how far away the moon actually is. One way to accomplish this is to start with a large frame of reference that we have some reliable measurements on, such as Earth itself.
For this example, we can simply imagine Earth as a giant blue marble, as depicted in the popular NASA photograph of Earth taken by the crew of Apollo 17 back in 1972. If we were to line up several of these giant blue marbles, side by side, how many would it take to reach the moon? Luckily, with a simple equation, we can figure this out really easily.
The distance from Earth to the moon divided by the diameter of Earth equals the number of Earth’s it would take to reach the moon.
We already know the distance from Earth to the moon is 238,900 miles, but what about the diameter of Earth?
Figuring out Earth’s diameter
The quickest way to figure out Earth’s diameter is to simply look it up online, where we can easily see that its diameter at the equator roughly 7,926 miles, but if that’s not challenging enough for you, here is another method to consider.
In a previous article I wrote, called The speed of Earth’s rotation, I learned that the circumference of Earth at the equator is almost 24,900 miles, so we can also figure out its diameter using this piece of information. The formula for figuring out the diameter of a circle based on its circumference is (C / Pi = d), so if we divide the circumference of Earth at the equator (24,900 miles) by Pi (3.1415926535), we get its diameter of 7,926 miles, which is exactly what we were expecting.
Calculating the number of Earth’s it would take to reach the moon
Now that we’ve figured out Earth’s diameter, we can complete the original equation, which is to divide the distance of the moon from Earth (238,900 miles) by the diameter of Earth (7,926 miles), which gives us just over 30. That’s 30 Earth’s away!
In most images of the moon next to Earth, it looks like it’s just a hop, skip, and a jump away—but the image just above this paragraph represents the actual distance, to scale, based on the size of both Earth and the moon. Now, the next time you stare up into space on a beautiful starlit night, you’ll know that the man in the moon is actually looking down at you from really, really far away!