HowDoWhy

When dealing with measurements on an orbital scale, you have to think big. As my previous astronomy posts have shown, the distances are vast. Though humans see and use numbers like million, billion and trillion all the time, our brains have a tough time conceptualizing what those numbers really translate to. How often, for example, have you held a million individual items in your hands? Or seen them in a room?

Yankee Stadium, for example, has a seating capacity of 57,545 people. If you’ve ever watched a game there you know what a “sea of people” looks like. Everything blurs into a cloud of colors. From a distance you might be able to take the whole scene in but it’s pretty staggering when you realize that the blurry mass of “things” sitting in all those seats are all individual people.

Well, to get to 1 million, you’d need more than 17 fully packed Yankee stadiums. Now think on an astronomical scale. The distance from the Sun to the Earth measures just shy of 93 million miles. If every person in Yankee stadium were a mile tall, you’d need 1616 filled stadiums worth of mile-tall humans lying head to toe to stretch from the Sun to the Earth.

So you can see that the numbers game in space doesn’t do well when we try to measure using things we can conceptualize. Even measuring from the Sun to the Earth is hard to grasp using common terms and, in the grand scheme of things, the Earth / Sun distance isn’t even all that big compared to other stuff in our solar system. Enter the Astronomical Unit or AU.  

The Astronomical Unit serves as a convenient measurement for things within our solar system. It is simply the average distance from the Earth to the Sun. So, one AU translates to about 93 million miles (92.9558 million miles to be exact). If one astronomer were speaking to another about a spaceship currently halfway between us and Jupiter, they’d say it’s about 2.1 AU from Earth. If their friend from the botany department strolled by and asked them what the heck 2.1 AU mean, our astronomer friend would quickly translate that to about 195 ½ million miles.