Making Distances in Space a Bit Easier to Imagine

 Warning to my readers: I’ll be using some big numbers in this article. Hopefully, I have made it as painless as possible.

Distances to objects in space from Earth are, well, astronomical. The Moon is 239,000 miles away. We’d have to travel 93,000,000 miles to reach the sun. That may seem like a great distance, but the next closest star, Proxima Centauri, is 22,876,214,400,000 miles away. Proxima Centauri is the closest of a three-star system known as Alpha Centauri. Using miles as a distance measure in space is quite impractical. The numbers get very big very quickly. Instead, we use light-years, the distance light travels in one year.

Artist's rendering of the Alpha Centauri three-star system. Credit NASA's Goddard Space Flight Center Conceptual Image Lab

Light travels at the fastest possible speed, moving through space at 186,000 miles per second. That’s 669,600,000 miles/hour or 5,865,696,000,000 miles/year. We call that distance, 5,865,696,000,000 miles, one light-year. Proxima Centauri is 4.25 light-years away, which is easier to write.

Let’s think about those astronomical distances in terms we can more easily visualize. Imagine one light year equals one mile. We all have a good understanding of how long a mile is. On this scale, light travels 0.002 inches per second. That’s a big change from the actual speed of light. The moon is 1.3 light seconds from Earth, or 0.0026 inches with this new light-year. We would orbit the sun, 8.3 light minutes away, from a distance of just under an inch. Proxima Centauri is 4.25 light years away, which now equates to 4.25 miles. Now it’s a lot easier to imagine these distances.

The fastest speed that any of our spacecraft has ever flown is the Parker Solar Probe. It used multiple gravity assists from Venus to get it close to the sun. It orbits so close to the sun that it passes through the sun’s outer atmosphere. In order to orbit the sun that closely, it has to move fast, achieving a maximum speed of 430,000 miles per hour. That’s really moving. But scaled to our new light speed of one mile per year, that corresponds to a mere 0.00064 miles per hour. At that speed, it would take 1,557 years to reach Proxima Centauri. Even in this shrunken universe, our Milky Way galaxy is 100,000 miles across, and our closest comparably large galactic neighbor, the Andromeda Galaxy, is still a mind-numbing 2,537,000 miles away.

As you can see, our universe is so incredibly large, even when shrunk by a factor of 5,865,696,000,000, it’s still huge beyond easy comprehension.

 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

This is reprinted with permission from the Oklahoman and www.Oklahoman.com.