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Mapping What You Cannot See, Cannot Know, Cannot Visit

Sunday, September 07, 2014 - 11:44 AM

When I was a boy I had a globe. I could take it in my hands, rest it on my lap, give it a spin and look down on Africa, Europe, North America and Asia spinning by.

In 1961 (I was 13), cosmonaut Yuri Gagarin left the planet and got high enough to look down on the real Earth spinning beneath him. He was the first (followed by Alan Shepard and later John Glenn) to gaze with his own eyes on what we had over the centuries so carefully mapped, drawn and imagined. From 160 miles up, you can take in the whole boot of Italy, the Red Sea narrowing to Suez, North America tapering down to the isthmus at Panama, and the amazing thing — amazing to me, anyway — is that what we'd spent 2,000 years drawing in our heads was actually there. We'd gotten it pretty much right!

Of course, you say. Cartography is a science. What it describes should be there. And yet, I find myself a little surprised by our ability to measure, to extrapolate, to conjoin, to build a true whole from a gazillion little parts. It's an enormous intellectual feat. And now, I'm happy to report, it's been done again — on a scale that boggles my mind.

The Laniakea Superstructure
Nature Video/YouTube

R. Brent Tully an astronomer at the University of Hawaii, Manoa, and his team have mapped a hunk of the universe that is 500 million light-years across. It contains 100 million billion suns — including our own little star. Their new map, like our early Earth maps, is built from detailed observations, intense data crunching and, when assembled, it pictures a galactic neighborhood he calls "Laniakea" — that's a Hawaiian name that the video below translates as (oddly) "immeasurable heaven."

Laniaka and Perseus-Pisces supercluster
Nature Video/YouTube


But they measured it. What you will see in this video is the first coherent map, not of our Milky Way but of the Milky Way's larger neighborhood, a branching "supercluster" of galaxies, being pulled, pushed and splayed over what I thought would be an unimaginable, unmappable distance — but here it is. As the video will show you, we are at the far, far edge of a long branch of swirling stars, an impossibly small seed dangling from an immense tree of light.

A Postscript: We Have Done This Before

Looking at this, I'm reminded that we have been imagining spaces we cannot see for thousands of years.

Back in 240 B.C., in ancient Alexandria, an astronomer named Eratosthenes got a letter from southern Egypt. The letter writer commented that where he lived there's a day — the longest day of the year (what we would call the summer solstice) — when a person casts no shadow. None at all. At exactly noon where I live, the southerner wrote, the sun is directly over my head, not a single degree north, south, east or west. For that moment, I am shadowless.

Me And My Shadow

Hmm, thought Eratosthenes, that doesn't happen where I live. Here in Alexandria on the longest day of the year at noon, the sun still casts a slight shadow. That got him thinking: What if the Earth is curved? Maybe sunshine is falling straight to Earth, but the shadow I see in Alexandria is telling me that I'm at a different angle to the sun than my friend down south? Maybe these shadow differences are telling us we are living on a giant sphere.

He measured the distance between Alexandria and Syene, Egypt, where his friend lived. Then, on the next solstice, he put a stick in the Alexandrian ground, measured the shadow at noon and was able to calculate (using trigonometry, based on the different lengths of shadow) how big the Earth might be.

What's amazing is he got very close. He imagined an Earth bigger than the one we live on, but since we don't know how Eratosthenes measured distances exactly, his calculations were either 16 percent too big or just 2 percent too big. Either way, he was conjuring up an immense ball, hundreds of millions of times bigger than he was, and when Yuri Gagarin got to see what Eratosthenes had imagined, it turns out, Eratosthenes was pretty much right. Go figure. 

(Come to think of it, that's what Eratosthenes did. Using a stick, a shadow and his head, he figured out what he was standing on. On our good days, we humans are very, very good.)


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Comments [7]

Excellent article! Check out my articles on:

Sep. 25 2015 07:58 AM
Lyn from Colorado

Thanks, Mr. Krulwich. That's breathtakingly beautiful. How lucky we are to be alive in this time and space, to begin to be able to see and understand the beauty of our night sky.

Sep. 18 2014 04:57 AM
Lynne from Cumbria

The image has the look of a pair of lungs. Reminds me of a theory of the expansion of the universe that I heard as a child - that the universe first expands then collapses ad infinitum, as though it is breathing. A living, breathing entity.

Sep. 17 2014 04:53 PM
Lauren Usher from Virginia

This is exactly why I wish to study to cosmos. One of the questions I thought was "why are certain parts moving towards one another? Why is gravity stronger there?". They mentioned the black voids within the Universe. Can you even begin to imagine what it would look like there? True black. No light for....well who knows how long.

Sep. 17 2014 11:45 AM
Joe Stone from Indiana

Are the Laniakea and Perseus-Pisces superclusters actually positioned as in the video, or were they placed side-by-side for comparison?

As an analog electronics enthusiast, that positioning really sparks my imagination. The opposing lines of movement resemble a magnetic field.

Sep. 15 2014 08:17 AM

Eratosthenes is actually one of my heroes.
What Robert said about us on our good days is kind of relativistic, though - as in we can see ourselves as being pretty resilient and at the same time so terribly fragile that one wonders how we could have made it this far.
As for us being good on good days, it's on those same days when we also bury such revelations as been brought to light by the likes of Eratosthenes sometimes for hundreds of years. One might have a huge point when saying that before the arrival of the internet making profound knowledge universally, that is terrestrially available was pretty much continuously hampered with.
Our good and our bad days, they're filling the week by an equal 7 days. Who knows where we'd be right now if these discoveries had been made both priority and public property from the beginning, and throughout until today. We'd be where our abilities indicated us to be; instead we're centuries behind.

Sep. 15 2014 07:09 AM
Matthew from Minnesota

It's incredibly astounding that as we look incomprehensibly large, it reflects the barely comprehensibly tiny. The way the organizations of galaxies function, act as a tree or field of energy shows how truly linked the small and large are in a poetic and comforting way. A mouse and an elephant share over ninety percent of their DNA. As I looked at the image of the web of galaxy superclusters, I kept imagining energy traveling across each pocket of matter like electricity going between neurons. It looks like a billion year thought.

Sep. 12 2014 03:43 PM

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