The Moon is Earth’s closest neighbour in space. Its orbit around Earth is elliptical, rather than circular, which means that its distance from us varies. At its closest point to Earth (its perigee), the Moon is 384,400km (240,000 miles) away. Incredibly, the Moon’s orbit is slowly carrying it away from Earth at a rate of around 5cm (2in) a year.
The distance between London, where I live, and Oxford, where I used to live, is about 100 km (or 60 miles). It takes about 90 minutes by car and about 120 minutes by bus. I can easily make sense of that distance.
Harder to consider: the distance between the Earth and the moon, which is 384,400 km (240,000 miles). It’s a fact we’ve likely all learned in high school. Unlike the distance between London and Oxford, however, it’s not easy to comprehend what 384,400 km means in real terms.
Luckily, you don’t have to think too hard. A NASA spacecraft has solved that problem for us. In October, OSIRIS-REX, a spacecraft that’s bound to intersect an asteroid in August this year, took the photo above from about 5 million km (3 million miles) away from the Earth. NASA posted the picture on Jan. 2, providing the public with a unique view of our planet and its moon. The angle is great to get a grasp of what the distance between the two celestial bodies really looks like, but it’s not perfect.
Here’s a back-of-the-envelope calculation to explain why. For ease, we’re going to use round figures. The Earth’s diameter is about 13,000 km (8,000 miles). That means, in the 390,000 km distance between the Earth and the moon.