“Through space the universe encompasses and swallows me up like an atom; through thought I comprehend the world.” -Blaise Pascal
So what I’m going to do is start off in the vicinity of Earth and go “up” by approximately a factor of 100 every time. Let’s begin.
Ahh, outer space. Looking down at the Earth from a distance, what would you see? Well, other than the planet itself, you’d see the (literally) thousands and thousands of satellites that are currently up and orbiting our planet. Most of them are just a few hundred kilometers (or miles) above the surface, but there are a large number of geostationary satellites, that orbit the Earth with the same period as the Earth’s rotation, farther out.
But what if we moved 100 times farther away from the center of the Earth, and looked back?
Some of our most sophisticated satellites and telescopes, such as WMAP, Herschel and Planck, are out beyond the orbit of the Moon! Moving 100 times farther away puts us at their location, with the Earth and Moon easily enclosed in that area.
But you want to get a different planet from Earth? Try going up another factor of 100.
And now, instead of just some satellites and the Moon, you get all of the inner, rocky planets, the Sun, and the asteroid belt!
But out journey is just beginning. Another factor of 100 will take you far.
It will take you, in fact, out to the edge of our Solar System! Getting all the planets, the Kuiper Belt objects, and even the farthest satellites we’ve ever sent (the Voyagers and Pioneers), another factor of 100 will take you out just past the heliopause, and into interstellar space.
But we haven’t gotten to another star, yet. Try going up by another factor of 100!
And — believe it or not — that won’t get you there! Going out 100 times farther than the edge of the Solar System will not even get you to the nearest star! (Not including our Sun, of course.) But it will let you see the entire Oort cloud, where (we believe) there are billions of frozen objects, just waiting to pass close enough to a star to melt a little, grow a tail and become a comet.
It’s time for another factor of 100, and what do we get?
At last, the closest stars to our Sun are in full view! Alpha Centauri is typically what we think of as the closest star to us, at 4.3 light-years distant, but it’s actually a system of three stars!
The two binary stars, Alpha Centauri A and B, are both somewhat Sun-like, and may have planets (with or without life) orbiting them, but the third small, distant member of the system, known as Proxima Centauri, is actually the closest star to us, at just 4.24 light-years!
So now, we’ve got a few stars within sight. What happens if we go up by another factor of 100?
That’s what I’m talking about! Most of the bright stars in our night sky, such as Sirius, Capella, Vega, and Arcturus, are now all within view. The closest open star cluster to us — the Hyades — as shown below, is here, too.
So now we’ve got thousands and thousands of stars, including an open star cluster, and you think you’re ready for your next step?
Okay, another factor of 100, coming up!
We get the whole galaxy! Spiral arms, the bar in the center, over 100 globular clusters, gas, dust, new stars, old stars, dying stars, future stars… all of it! Pictured above, of course, is not our galaxy, but NGC 6744, what we think of as our galaxy’s “twin”.
It’s a beautiful sight, to be sure. And you might be wondering, after what we just went through with our Solar System and the next nearest star, if the next step of “100” will get you to the next nearest galaxy or not.
Ready to find out?
Unbelievably, galaxies are much harder to escape from on these scales! We not only get the entirety of our local group, including M31 (Andromeda), the Triangulum Galaxy, and the Magellanic Clouds, among others, but we also get other groups of galaxies, including the spectacular M81 group, shown below.
So you might be wondering if the next step up will take you to the spectacular galaxy clusters we find in our Universe. Let’s find out! Another factor of 100 gets us…
A spider web? Oh, no. You see, in the image above — courtesy of the 2 degree Field galaxy redshift survey — each pixel in that image is an entire galaxy.
What you’re seeing is how galaxies cluster on the largest scales in the Universe. And the answer, unsurprisingly, is in great clumps and filaments. The densest clumps — like the Coma Cluster (below) — make up grand galaxy clusters.
But those grand filaments? The collections of galaxies in great lines across space? Those are even larger features. The largest ever discovered, in fact. The greatest one — in size — that we’ve ever seen? The Sloan Great Wall, about a billion light-years across, below.
This thing is so big that it isn’t even gravitationally bound to itself all the way across! That’s right! Over time, this object will fragment into many smaller clusters, as dark energy and the expansion of the Universe will tear this “great wall” apart.
And so — one last time — we go up by as close to a factor of 100 as we can. (A factor of about 47, in fact.)
And we come to a baby picture of the Universe, when it was only 380,000 years old. 46.5 billion light years away, this nearly-uniform light is the leftover glow from the big bang. Slightly “hot” spots indicate an underdensity of matter by less than 0.01% from the average, while “cold” spots indicate an overdensity by the same amount.
The hottest spots will eventually shrink into great voids, where galaxies and structure are very sparse and rare, while the coldest spots will gravitationally attract more and more matter, and will grow into galaxies, clusters, and — for a brief time — great walls.
But I have something even better. No, not the xkcd height comic, even better than that. Courtesy of Gott et al., 2005, ApJ, 624, 463, comes the true scientist’s version of a Logarithmic map of the Universe, from the surface of the Earth all the way up to the farthest reaches of the known Universe.
A full, 300 dpi printable version is available here. I hope you enjoyed this phenomenal tour of the different distance scales in the Universe, and thanks for “going up” with me!