How Big is Space?

One thing you should know about space: it's huge. Mind-bogglingly huge. If you were to think of the biggest thing you could possibly imagine, it would still be more than a billion times bigger than that (and don't say you imagined infinity, because you can't. And stop being clever). The problem with just saying "the universe is huge" is that it doesn't really convey the distances involved. We can talk all we want about light-years and parsecs (unit of distance, not time, sorry George Lucas), but it doesn't really mean much. They're just words. And, as wonderfully evolved as language is, a lot of scientific terms fail to covey conceptual content with them, because our brains simply didn't evolve to deal with this sort of stuff. So this Friday, I'm going to try to take a stab at this comprehension.

Let's start with something simple. The moon. The moon is the closest natural thing in space to us, and, at the closest point in its orbit (its perigee), it's about 225,623 miles (363,104 km) from us. That's quite a lot of miles. For perspective, the width of the continental United States (not including Alaska) is about 2,100 miles. If you were travel all the way around the Earth at the equator you would cross 24,901 miles (40,075 km)—a trip that would take you somewhere between one and two days nonstop in a plane. The moon is about nine times that distance from Earth. A bit of a hike, if you will.

What about the sun? It's about one Astronomical Unit (AU) from us&mdas;as an AU is defined as the average distance from the Earth to the sun, at approximately 93 million miles (150 million km). That's over 400 times the distance that the moon is from us (and good thing, too—the sun is 860,000 miles in diameter; if it were as close to us as the moon is, we'd be inside it). To get a better scale of this distance, let's apply something banal and totally impractical to it. Let's say you have decided to go on a family vacation to the sun, mostly because you operate under the completely irrational assumption that the ideas you have at two in the morning are great ones. Lucky for you, the highway committee also operates on the same principle, and just recently built, at great expense and headaches, a highway straight to the sun. The toll's outrageous, but you can still drive there. Let's also assume that the highway is the same boring sort of highway we see normally in America, with a speed limit of 65 mph. Let's also assume that you drive on it much like you drive on a normal highway, at about 80 mph. Now, at 80 mph, how long would it take to reach the sun (assuming you never stop to eat, sleep, or refuel)? At 80 miles an hour, over 93,000,000 miles, it would take you a little over 132 and a half years. Let's now say that you booked a flight instead (as in this entirely ridiculous fictitious scenario, planes also fly to the sun, despite lack of air or means of escaping the Earth's gravitational well). The average velocity of a commercial airliner is 550 miles per hour. At that rate, your trip would only take a measly 19 years. At least you'd survive to see it by then, if the airline food hasn't killed you. Now, if nineteen years still sounds like too much time to take off for vacation (well, 38 for the round trip), you could hitch a ride with NASA and nab a rocket (which they still produce and launch domestically in our fantasy). So you managed to get a spot on one of NASA's rockets destined to break solar orbit (which you proceed to redirect toward the sun). This rocket goes at a whopping speed of 36,500 mph, which would bring down your commute time to 106 days. Still, a little under a third of a year isn't too bad, relatively speaking.

Now what about our other neighbors? We've been to Mars, which is, at its closest to us, closer than the sun. But Jupiter, the first of the Outer Planets, is about 390 million miles away from us at its closest—four times further away than the sun. If we extend our gaze to Pluto (not a planet, of course, but the most well-known body in our solar system further out than Neptune), we're looking at a distance of about 3.5 billion miles—11 years in our rocket. And that's just stuff within our own solar system.

The next closest star to us is Proxmia Centuri, at 4.2 light-years away. How far, though, is a light-year? Light moves at a mind-boggling 186,282 miles per second. It moves slightly over 11 million miles in just a minute, and 670 million miles in an hour. It takes light just 8.3 minutes to get from the sun to the Earth, over 18,000 times faster than our rocket. In a day, light travels over 16 billion miles. This clocks in at 5,874,589,152,000 miles—over 5.8 trillion miles—in a year. That puts Proxima Centuri at 24.5 trillion miles away. Our rocket would take seventeen and a half thoursand years to travel one light-year, putting Proxima Centuri at 74 thousand years away from us by rocket. And that's just the closest star to us.

If you were to look at the night sky, you could probably easily pick out the star Sirius, which is about 2.6 parsecs from Earth, as it's the brightest star in the night sky. Note that we've introduced a new term, a parsec. A parsec is most easily remebered as 3.26 light-years (about 19 trillion miles). This puts Sirius at about 50 trillion miles away from us—155,000 years in our trusty rocket. For reference, humans only evolved about 200,000 years ago. An additional fun space distance fact: Sirius is 1.5 million miles in diameter, almost twice the size of our sun.

Now we move from the extreme to the ridiculous. The distance from us to the galactic core is (conservatively) about 25,000 light-years, or about 150,000,000,000,000,000 miles (150 quadrillion miles), which is about 450 million years in our rocket (that's before life even made it out of the ocean). The distance from us the the next nearest (non-dwarf—the nearest dwarf galaxy is Canis Majoris, which is about as far away from us as the galactic center is) galaxy, Andromeda, is 778,000 parsecs, or about 2.5 million light-years. That's 1,500,000,000,000,000,000 miles—1.5 sextillion miles, which is about 46,000,000,000 (46 billion years) in our rocket—that's about three times longer than the universe itself has existed (it's only about 13.7 billion years old). And that's only the beginning. Take a look at the Hubble Deep Field—every point of light in that image is a galaxy. The hubble was pointed at a tiny, seemingly blank portion of the night sky, and that was the result. The universe is enormous. Beyond huge. It defies comprehension or classification. And we're just hurtling through it clinging to the surface of this tiny little rock. Brings a sense of scale to everyday life, doesn't it?


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