How Big is the Solar System?
The scale of the universe: impossible for the human mind to comprehend?
Comprehending the vastness of the universe in everyday terms
If you're anything like me, there comes at least one night every week- and sometimes quite a few more- where your mind decides it's going to play a little game of "show the body who's boss." It's not a fun game for me to play, but my brain does it anyway, and for the longest time, the only thing that seemed to solve the problem was to open up a book (paper, not tablet or computer screen) and read until my eyelids drooped, much to the chagrin of whoever shared the room or bed with me.
Well, there's another way you can exercise (and, ultimately, tire out) your brain and find a way to fill yourself with wonder, while falling asleep with an inner peace that only comes from satisfying the urge to ponder deep concepts. Here are five concepts that help me ponder the awesome scale of the universe just enough so that I can fall asleep. One rule stands: I won't use a calculator for any of the math, because I'd have to do it in my head if I was falling asleep, and I'll use approximations any time I'm not sure of the exact measurement beforehand.
The distance from the earth to the moon
Google will tell you more or less immediately that the moon is roughly 239,000 miles away from the earth. There are two ways I can connect this to my everyday understanding, so that I can somewhat begin to comprehend such a vast distance. The first is that I actually drove one of my cars (a 2000 Toyota Corolla, rest in peace) almost exactly 239,000 miles over the course of about 9 years. All of the driving I put together over the course of that 9 years- and that was a lot of driving- would amount to a one way trip to the moon, if highways stretched up there. The second way to think about the distance is a bit more linear- if I was driving at 60 miles an hour... no, let's round it off to 50 miles per hour to make the math easier- that would put me at 600 miles traveled in a (very exhausting) 12 hour day. If I had another person in the car with me and we both drove 12 hours a day every day, peed in a bottle or something and had plenty of fluids and food brought in to us, we'd make 18,000 miles in 30 days (600 miles a day times 30 days in a month). Let's round that up to 20,000 (because this is about understanding scale for me, not getting all the math exactly right). 20,000 miles in a month gives you roughly 240,000 miles in a year, so that gets you to the moon! Whew, that trip would really, really suck.
The distance from the earth to the sun
OK, now that we've got a mental image in regular, everyday terms (driving for a year, 24/7, 50 mph) for how to get to the moon, what about the sun? Let's start by figuring out how far the sun is. "They Might Be Giants" sings about this... how does it go? Oh yeah! 93 million miles. It's also 8 light minutes, and I'll get to that in a sec.
93 million miles is around 93 times 4 trips to the moon (if we round the distance from the earth to the moon to 250,000 for easy calculation, since 4x250,000 = 1,000,000). Easy enough to start. So 4 x 93 is around 400. That means you'd have to drive nonstop for 400 years at 50 miles per hour to get to the sun! Wow. And yet, light travels that same distance in 8 minutes. If light left earth to head to the sun when I started typing this, it would be arriving at the sun right now. If I had left to drive to the sun, nonstop at 50 MPH, 24/7, on the day that Pocahontas had married John Rolfe, I'd just now be arriving at the sun. How's that for scale?
The relative size and distance of the solar system
This is one of my favorites, because it really shatters some old illusions held since childhood about the scale of the universe, and especially the solar system. I know that the sun is around 600,000 miles across, and I also know that the earth is 93,000,000 miles from the sun. Finally, I know that the earth is about 8000 miles wide (it's okay to peek at Google for a second if you need to know these ballparks).
So what does that mean to me? Well, let's say the sun is roughly the size of a basketball, or around a foot across. There are 3 feet in a yard, and 100 yards in a football field, so I can kind of put the earth-sun system in a football field for context, with the sun as a basketball at the edge of one end zone. The sun is more than half a million miles across, and the earth is less than 100 million miles away. That means that, using rough numbers, I'd need to put the earth around the 50 yard line, give or take. But how big would the earth need to be? Well, it's around 1/100th the width of the sun, and if the sun is that basketball, the earth would need to be around a hundredth of a foot, or close to a tenth of an inch in diameter. I'm going to say a BB pellet is pretty close to that.
So a BB pellet at the 50 yard line, a basketball at the end zone, and that's the earth and sun, and the distance in between. Seems kinda different than what I was shown in school, and it really gives me a sense of the vastness of space.
"The universe is a pretty big place."
Just a step further
If that gives you pause to think, this will knock your socks off (or, hopefully, put you to sleep... I find that I do some great deep thinking as I'm drifting off to sleep). Consider how far it is from the sun to the next star: 4 light years, give or take. Recalling that the sun is a basketball at the end zone, and the earth is a BB at the 50 yard line, and 8 light minutes is the distance from the earth to the sun, can we do the mental math without cheating on this one? I think we can:
The earth-sun distance, 8 light minutes, is 50 yards, so in one hour, light travels 8 times the distance from the earth to the sun (roughly), or 400 yards. Okay, four football fields. I can see that. But how many hours are in four years? Let's back up a little.
400 yards is about a quarter of a mile (recall that 3 feet are in a yard, and 5280 feet are in a mile). OK, so our "light" travels a mile in 4 hours, or 6 miles in a day. Now I think we're getting somewhere! 6 miles in a day times 1500 days in 4 years (365 x 4 ballparked in my head) is 9000 miles.
Earlier, we said the earth is about 8000 miles wide, which is pretty damn close to 9000. If you put a basketball on one side of planet earth to represent our sun, then another basketball on the other side of the earth could fairly represent the distance to the next star over, Proxima Centauri.
Now that's hard to imagine. What if I made the sun the size of a BB? Well, the BB is around 1/100th the width of a basketball (or so we figured earlier). 1/100th of 9000 miles is 90 miles. I live in Richmond, VA and I have a BB. My buddy in Washington, DC has a BB that represents the nearest star to our sun, and the planets revolving around our sun would be too small to see without a microscope.
What other crazy analogies will our brains dream us as we're drifting off? Who knows, but I'm going to write some of them down.