In the 4th century B. C. E. (Before Common Era), scientists believed the Earth was the center of the universe. Before that, they were convinced the Earth was flat.
Now, if anyone so much as mentions that the Earth is the center of the universe, they are quickly corrected. The very idea is absurd. (Although there are in fact online “societies” for people who believe the Earth is flat.)
We now know that not only is the Earth not the center of the universe, but neither is the sun, which is undeniably the center of the solar system. Were we to zoom out much further and take a look at our galaxy, the Milky Way, we would find that the sun is not even near the center of its own galaxy.
In fact, it’s located in a small “spur” of stars just off one of the spiraling arms of the galaxy. Since the current theory states our universe is infinite, there can’t even be a center, and thus our galaxy is not the center of everything. How wrong those early astronomers were!
But what does all this mean? Where exactly are we in the universe?
If you’re familiar with your home address, which I assume you are, then the first part of the answer is easy. You live in a certain house, on a certain street, in a certain part of town. Imagine, somewhere in your area, a region about fifty feet across with a single bench where you sit. From far enough overhead to get the entire region into view, we can still see you. You are about a centimeter tall.
Now, let’s pull back a bit. Imagine a region 100 times wider than the preceding one. We are now looking over a city, and the previous region is smaller even than you appeared within it.
Now let’s pull back a bit farther. But before we do, don’t forget to transition over to the metric system of measurement (if you don’t use it already). I’ll let you in on a little secret—it’s taken me forever to get used to the metric system, and I still have to refresh my memory every time I come back to it. That’s the burden of growing up in the States. We may arrogantly expect our immigrants—and, weirdly, everyone else in the world—to learn our language, but at least we have to learn everybody else’s when it comes to scientific measurements.
Where were we? Ah, that’s right. Our current field of view is about 1.6 kilometers across. Now let’s expand that by another factor of 100. Now we see a patch of land about 160 km across. (Easy enough conversion? To expand by 100, just move the decimal point over two digits. Why? Because there’s two zeros.) From this far above, we definitely can’t see you, sitting on that bench in the park. What we can see are some of Earth’s natural features. We’re getting more realistic, now.
Let’s pull back again. This time, expanding our view by a factor of 100 shows the entire globe. And it’s quite a sight, isn’t it?
To us little people, our planet alone seems huge. And yet, it’s not an insurmountable distance. Cross-continental travel once took months or even years; now we can fly across our oceans and land masses in planes. We can drive at extraordinary speeds down freeways. And we’ve gotten much farther than our own planetary surface. We’ve launched rockets and shuttles and landers and satellites and probes…oh, you name it, it’s out there. The one thing we have yet to achieve is the assembly and launch of a starship. (Okay, well, maybe that’s a bit far in the future…but it doesn’t hurt to wonder!)
That brings me to our next field of view: the moon’s orbit around the Earth. We have pulled back by another factor of 100. Actually, this image really isn’t to scale with that expansion—the textbook does a much better job of demonstrating the actual distances at work here—but come on, work with me. I’m literally grabbing these off the Internet.
Another thing I’d like to point out here is that while the sizes of the Earth and moon are to scale, their sizes relative to the moon’s orbit are not. Were the Earth seen from the right distance to make it appear that size, the moon would orbit much farther out. But…again, work with me here.
My point is, well…we are really really small. As you will see in the next expansion by a factor of 100.
Okay, so…ignoring the weird numbers and angles in here, the line between the Earth and the sun is a distance known as 1 astronomical unit, or 1 AU, which equates to 93 million miles (or 1.5 x 108 km). And this is pretty much the smallest, most basic unit of astronomy, like centimeters down on tiny little Earth. We literally can’t even see the continents. In fact, Earth is drawn too large here to be realistic, considering the size of the orbits! The universe is huge.
Now, we’re getting to the real distances. How often do you measure anything in your daily life in centimeters, honestly? (And don’t answer that if you’re from America, we both know centimeters take a backseat to inches over here.) I’m going to pull us back by another factor of 100, and now we can see the solar system. The whole entire solar system. But I’m going to pull us out again, and now we’re not so close to home anymore, are we?How about if I pull us out by another factor of 100?And another?That’s an artist’s conception of the Milky Way Galaxy, our home in the cosmos. It is known as a barred spiral galaxy, a spiral in which the central “hub” is shaped like a bar rather than a round bulb. It is made up of something like 100 billion individual stars. Other galaxies can be elliptical, and some have entirely different, but utterly fascinating, shapes. But…would you believe there’s still really far to go?
Here, I’ve pulled us out by yet another factor of 100. I think it’s telling, really telling, that astronomers—the same people who have been studying the wonders of the universe and accumulating data and evidence for a few hundred years—refer to this group of whole galaxies as our local group.
What do you think of when you hear the word “local”? The coffee shop down the street? Your school? Your work, if it’s nearby? The park in town?
Okay, these are whole galaxies. Many of them contain over 100 billion stars. Some of those stars may be like our sun; others are hotter, cooler, larger, or smaller. Some have solar systems. In fact, we are discovering an increasing amount—I think the count is well over a hundred now—of planets orbiting other stars. So, think of this: there are over a hundred, likely more, potential Earths and Jupiters out there, orbiting stars of their own, and there are sometimes over 100 billion such stars in any one galaxy, and our galaxy is part of a neighborhood of other galaxies that, together, is called the Local Group.
So if this is like a neighborhood, then what constitutes a city? A country?
Goodness, now we’re talking big.
And I haven’t even gotten to the biggest grouping of all: the superclusters and filaments.
Time to take us out by another factor of 100. Our field of view is now far more than 17 million light-years across. Light-years are huge. Have you ever noticed how fast the light from your flashlight hits its target? Well, it doesn’t happen instantaneously. That’s just the speed of light. And one light-year is the distance light can travel in a whole year.
Pretty damn huge.
Guys. <clears throat> This isn’t a starry night sky. Those speckles aren’t stars. They are whole galaxies.
Every single one of them. A whole galaxy. Every single pinpoint contains, on average, over 100 billion stars. And…ahem…there is space between these galaxies. Lots of space. In fact, we know from our own space program just how hard it is to reach our moon. If there’s so much space just in our solar system, imagine how much there is in a whole galaxy? In a group of separate galaxies?
Now this just blows my mind. Now we really are small.
So, in the future, when I talk about Earth as our little backwater planet, you’ll know what I mean. We are practically insignificant on the scale of distance the universe offers. Remember how many times we had to multiply the area of our field of view by 100? 50 ft x 100 x 100 x 100 x 100 x 100 x 100 x 100 x 100 x 100 x 100 x 100 x 100. Twelve times.
Yeah, Earth is tiny.
You may be wondering how the heck astronomers can possibly know these things. We’ve only got probes as far as the dwarf planet Pluto, and some of our long-term missions are just beginning to make their way beyond the solar system. We haven’t been able to hold out the selfie stick and take a look at our own galaxy from afar. How do we know that there are superclusters of galaxies out there?
Okay, truth is, that’s the whole point of my astronomy posts. Reading the textbook, discovering that for myself, learning what really is out there and how we know. Learning how to decipher the codes within the spectrum of light and read energy as astronomical data, and from that, drawing a picture of the world beyond our backwater planet. I find that absolutely fascinating. And I’d love to have you guys along for the ride.
So if you want all those answers, stick around. There will be more posts to come.