Space is unreasonably big.

Perhaps that’s the wrong adverb. We can use reason to try it understand it, but grasping it, getting a true intuitive understanding for it, is a whole ‘nuther story.

Space is too big to grasp. The numbers get so big so fast that analogies tend to break down; we can’t really get a feel for it. As an example, the fastest spacecraft leaving the solar system is currently Voyager 1, moving at nearly 17 kilometers per second relative to the sun. That’s already a ridiculously fast speed, over 60,000 kilometers per hour! That’s 600 times faster than a car on the highway. Who can truly absorb that kind of number?

Yet it’s practically motionless compared to the distances between stars. Proxima Centauri, the closest star to the sun, is about 4.25 light-years away, or 40 trillion kilometers; even at its breakneck speed it would take Voyager 1 seventy-six thousand years to get there.

Blarg. That’s too much for a human brain.

However, something a friend once mentioned to me many years ago makes this a bit easier.

The distance from the sun to Earth is about 150 million kilometers on average. That’s a useful unit to use in astronomy for various purposes, so much so that we gave it the rather glorious name of the Astronomical Unit, or AU. 1 AU = 150 million kilometers.

There are about 63,241 AUs in a light year. That’s a lot! Light only takes a little over 8 minutes to reach Earth from the sun, so in a year light travels a long way.

Here’s the fun bit: As it happens, there are 63,360 inches per mile (pardon the use of Imperial units, but that’s where the numbers work best). Those two numbers are very close; the difference between them is only about 0.2%!

That gives us an interesting scale to use. Picture Earth and the sun being one inch apart. On that scale, a light-year is a mile long! That to me is a graspable scale, and a terrifying one; a light-year is an immense distance. It takes months if not years for spacecraft to travel a single AU — just one inch on our imaginary map — so traveling a single light-year is well beyond an epic journey.

And that won’t even get you to the nearest star. If an AU is an inch, Proxima Centauri is 4.25 miles away. Is there a town or a store or a friend’s house 4.25 miles from you? Next time you drive there, think about how every inch you travel is like going from Earth to the sun (at highway speeds, it takes about a millisecond to travel one inch). Compare that to how long it takes you to get to your destination.

Yeah. Space is big.

And that’s just the nearest star. Even this scale breaks down in our minds rapidly. In the one-inch-is-one-AU scale, the bright star Betelgeuse is about 500 miles away. The Orion Nebula is about 1,300 miles away (for scale, in real terms Denver is about 1,500 miles from Washington, DC).

Our Milky Way Galaxy is way way bigger than you realize. At 120,000 light-years wide in real life, on our new scale it would still stretch halfway to the moon.

In other words, even shrinking our map hugely down in size, we still need astronomical analogies to describe how big our galaxy is.

As for humanity’s achievements, Voyager 1 launched in 1977, almost 50 years ago. On our inchly scale, in those five long decades it’s traveled 14 feet. Fourteen feet.

Sometimes, when I’m interviewed for a news program or podcast, they ask me what’s the one thing I wish people understood better about astronomy. There are a lot of good answers, but I almost always say “scale”. The depth of space swallows up our brains and envelops them in a dark, stifling vastness, so huge that it can actually be terrifying. This is why space exploration is so hard, this is why we still struggle to map even the nearest planets, this is why so much of the solar system is (literally) terra incognita.

Yet this knowledge is also uplifting: it’s amazing we can know anything at all about objects across these crushing distances. And we do; in fact we know a lot, and our knowledge grows every day.

Space may be formidably, inconceivably deep, but our brains are capable of traveling those distances vicariously in our imagination, and even more reasonably through our understanding of science. That to me puts everything in perspective rather nicely.

• You probably know I’m a big proponent of citizen science projects, so here’s a new one: looking for gravitational lensing in Euclid data! This is part of the Zooniverse project, so go there to sign up and help astronomers find warps in space!
  

• I’ve written before about how vegetation on Earth absorbs most visible light but is highly reflective in infrared (which is why trees and such glow an eerie silvery-white in infrared footage). Now, a team of scientists has looked into using this fact to see if they can detect vegetation on other planets! The answer is: possibly, which to be honest is better than I would’ve thought [link to journal paper].
  

• Scientists analyzing various meteorites to determine their composition have found measurable contaminants in them, including ink, adhesives, and lubricants [link to journal paper]. These clearly came from the handling and processing of the rocks, and are not native to them, raising an alarm that the way these precious resources are protected from contamination needs to be critically assessed and improved.

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