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How big is it, really?

People often say that standing outside on a clear, starry night gives you a sense of scale, of how tiny you are compared to the vastness of the universe. But it's tough to really comprehend just how vanishingly miniscule we are. We're so used to living in inches and feet and miles—or centimeters, meters, and kilometers—that it's nigh impossible to wrap our minds around the enormous distances between us and other objects in the universe, even ones we can see, like the sun and moon. Is there any way to comprehend it?

That may be a tall order, but folks at Agnes Scott College in Atlanta, Georgia have come up with a wonderful, creative approach in a project called MASS. MASS stands for Metro Atlanta Solar System, a model of the solar system scaled down by a factor of 150 million to fit within Atlanta's city limits. Agnes Scott's gorgeous Bradley Observatory is the center, specifically the circular stone courtyard in front of it. The courtyard's diameter is about 30 feet, providing the scale for the planets, the rest of which are located at landmarks around the city that are the right distance away. Earth is a little more than half a mile away from the sun, at Decatur Public library, while Neptune is 18.5 miles away at Sweetwater Creek State Park.

What I love about this idea is that it reaches towards the bigness of the universe by being on a scale that requires travelling miles to get from one planet to another. When we see a scale model of the universe that takes up a few square feet, it's hard to get a sense for comparative distances and sizes. But if you have to hop in a car and drive out to the edge of Atlanta to find Neptune, you get a better idea of what's in Earth's neighborhood and what's not. It's even clearer to Atlanta natives, who have an instinctive sense of the nearness of these locations. I can imagine people saying, "You mean Mercury's still on Agnes Scott's campus but Uranus is at the airport? Wow, that's far away." Or standing in the 30-foot-wide courtyard of the sun and then seeing the three-inch model Earth at Decatur Library might bring home the tininess of our home planet. (Here's a list of other cities that have scale universe models—in the Peoria, Illinois scale model, it will take you an hour and half just to drive from Pluto to Neptune.)

I'd love to see people take on other conundrums of scale in this way. But it turns out that when you go smaller and smaller instead of bigger and bigger, things become even more mind-boggling. Say you wanted to represent an atom with a sphere the size of a basketball. In this blown-up world, the basketball would now now be a little under 200 times the size of the sun. (A hydrogen atom has about the diameter of an angstrom, or ten trillionths of a centimeter, while the basketball has a diameter of about 25 centimeters.)

John Norton at the University of Pittsburgh frames the atom's tininess by offering you what seems at first like a sweet deal: an atom of gold for every second since the dawn of the universe.

Go inside the atom, and scale becomes even more astonishing. While a hydrogen atom is about an angstrom across, the proton at its center is five orders of magnitude smaller. If the proton is now a basketball, the atom is 15 miles across. The rest? Empty space. As for the electron, good luck pinning it down to measure how wide across it is. What we do know is that it's about 2000 times less massive than the proton. Here's a fun and kind of bone-chilling representation of just how much nothing there is inside the atom.


  1. To put the perspectve into perspective, imagine the United States, coast to coast, as our very own Milky Way Galaxy. The entire solar system would only be the size of a quarter, and good old planet Earth wouldn't be visable, by a long shot. Earth would be about 20 nanometers across, about a fifth the size of a virus. The sun, the biggest thing in the solar system has 109 times the diameter of Earth, would only be about as big as a bacteria!


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