True confession: I am easily distracted by strategy games on my computer. I have owned every version of Civilization since the original, and every Sim-* game since the original SimCity, other than the most recent one–and even that may change, now that Maxis has eliminated the “always online” requirement. I spend all day worrying about how my actions will affect other people; I don’t need a social game to compound that requirement.
This year, however, I started playing Kerbal Space Program (KSP), and was surprised to discover (like Randall Munroe) that I’m gaining an intuitive understanding of orbital mechanics, which I used to find counterintuitive. The other thing I find myself realizing is just how big the universe really is. That is to say, the magnitude of space is beginning to sink in for me. But to really understand this, we need to start closer to home, with a simple airline flight.
Your commercial flight is perhaps 10 thousand feet in the air, perhaps less, and since you finished your novel during the layover in Detroit, you look out your window at the view. “Wow, you think, those houses are so small. I’m a long way up in the air.” But you aren’t even two miles above the ground.
I don’t mean to belittle that altitude. I’m sufficiently acrophobic that the thought of falling a few dozen feet is angst-producing for me. Compared to space travel, though, this is really nothing. Astronauts in the International Space Station, for example, habitually orbit at an altitude of 230 miles above the surface of the earth.
For Kerbals in KSP, the numbers are a bit different, but the effect is similar. This picture shows an orbital altitude of 80,000 meters, which is roughly equivalent to low earth orbit (LEO) for kerbonauts, whose atmosphere is only a third as deep as ours. (From this point on, I’ll be using screenshots from KSP to illustrate this article, but I’ll try to use numbers from our solar system. I think the relative scales are still valid.)
Low earth orbit is a long way up, but compared to the earth, it isn’t a terribly big distance. In fact, you would travel roughly 230 miles if you drove from Buffalo, NY to the state capital in Albany. Compared to the size of the earth itself, LEO is practically touching the surface. Despite this, no human has gone higher than Low Earth Orbit since the Apollo program of the 1970s put men on the moon.
Since I grew up with the lunar landings as historical fact, I was never really impressed by them. Having played with KSP, though, I now realize just how stupendously far away the earth’s moon really is. At an altitude of more than 200,000 miles, the moon is three orders of magnitude higher than LEO.
By comparison, the distance around the world is only about 25,000 miles at the equator. To make his small step for man, Neil Armstrong travelled a distance equal to a trip around the world–more than nine times over.
This distance is so large, I didn’t really comprehend it until I took a look at the KSP-scale distance to the Mun, shown at left. In order to see it on my screen, I had to scroll back so far that the orbit of my spaceship (shown in blue) basically merged with the edge of the planet it was orbiting. And the ratio of those two distances is actually less than the real difference between the Moon’s orbit and LEO.
This immensity of scale is just the beginning, though. The planet Venus, our nearest neighbor, is never closer than about 23 million miles from us. That is roughly 100 times the distance from the earth to the moon. Once again, the scale is so tremendous that to visualize a trip from the earth to another planet, we have to zoom back so far that lunar distances disappear in the roundoff error of my first-order-approximate envelope calculations here.
Beyond our sun, the orders of magnitude just keep growing. The nearest neighbor to the Sun, Alpha Centauri, is 25 trillion miles away. This number, roughly 100,000 times the closest distance between Earth and Venus, is so large that we don’t normally talk about it in miles. Instead, the preferred unit is light years, with each light year representing the distance that light can travel in a year, or 5.8 trillion miles. At that scale, Alpha Centauri is a little over 4 light years away.
If you aren’t mind-boggled yet, consider this: the Milky Way galaxy is 100,000 light years across, and the next nearest galaxy, Andromeda, is 2.5 million light years away. There are other, more distant galaxies in our local cluster, and other galaxy clusters still further away. The local Virgo supercluster, containing our galactic cluster and its nearest neighbors, is bigger in light years than the earth’s orbit is in miles, or roughly the distance to the moon in feet.
Clearly, we have a long way to go if we want to explore the universe.