We don't make very good judges of distance, not on cosmic scales at least. Using our own wanderings on Earth as the judge of all things, evolution has left us poorly prepared for the epic scales of all things astronomical.
This week, as a box of electronics called New Horizons prepares to complete a nearly 10-year journey to Pluto, it's a good moment to reflect on just how far away even the objects in our astronomical backyard are from us.
When astronomers measure distances in solar systems their meter stick is the average distance between Earth and the sun. It's called an astronomical unit, or AU, and it equals about 93 million miles. Earth obviously lives at 1 AU from the sun. Mars is about 1.5 AU. Jupiter orbits out at around 5 AU and Saturn, with its gorgeous rings, lives about twice as far out at almost 10 AU from the sun.
So where is Pluto?
Unlike the other planets whose tracks around our star are pretty much circles, Pluto's orbit swings in and out on a highly elliptical orbit. It comes as "close" to the sun as 30 or so AU (inside Neptune's orbit) and as far out as almost 50 AU. At an average distance of 3.7 billion miles from the sun, wee Pluto lives in a world of perpetual twilight.
But exactly how far is 3.7 billion miles?
The problem with astronomical distances is simple. Once you get past a couple hundred thousand of anything, who can really tell the difference? How much bigger is 10 billion miles compared to 75 million miles? It's not like we have day-to-day experience with this kind of thing. So, what do we have visceral experience with when it comes to distance?
Driving. We do a lot of driving.
As everyone knows, being in the car for 10 minutes is not a big deal — but a 10 hour drive will suck the life out of you. That means we all use time to understand distance. Buffalo is an hour away from where I live in Rochester. New York City, however, is 5 1/2 hours. Washington, D.C., is 10 hours, Minneapolis is two days and LA is a long week of back pain, junk food, monotony and some spectacular views.
So, if it's a week to cross the country, how long would it take to drive to Pluto?
Doing the simplest calculation possible assumes a straight-line trip from Earth to the dwarf planet, ignoring each planet's motion as well as the need to stop and pee. In our calculation, we will also promise to be good and not speed, keeping a steady 65 miles per hour the whole way. And to keep things simple, let's use Pluto's average orbital distance of 39 AU. So, when we put all this together how long would our solar-system-spanning road trip last?
Just a mere 6,293 years (give or take a few decades).
Oh, come on now. Stop complaining. That's not so bad. It's actually less time than some creationists think the universe has existed. Of course, a 6,293-year-long road trip is not something you want to try with little kids. The asteroid belt is nothing but tourist traps, and the rest stops really thin out after Saturn.
Some of you will want to consider flying.
Luckily, at a Boeing 777's maximum velocity of 590 miles per hour, the trip to Pluto will take only about 680 years. Make sure you pick up some sandwiches and Cinnabons in the airport before you leave because you can bet the flight attendants are gonna run out of boxed meals before you even get past Mars.
So, when New Horizons zooms past Pluto on July 14, giving us our first view of the solar system's outer output, show some respect. Blown off the Earth with the fastest speed ever (for a launched spacecraft), it's now traveling at more than 50,000 miles per hour. The voyage that would have taken you more than 6,000 years in an SUV or 600 years in a jetliner has taken New Horizons a little under a decade. And after Pluto, New Horizons will sail through the Kuiper Belt (an extended ring of planetary construction debris) and out, eventually, toward the stars.
But that is another long, long, very long story.
Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described "evangelist of science." You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4.