Obliscent

“One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike—and yet it is the most precious thing we have.”

—Albert Einstein, Letter to Hans Muehsam, 9 July 1951

In the light of this 1898 Moon model, Mills observed the way we humans nest knowledge, building little models of the world in our own minds. Go read his post.

It’s awe-inspiring that both minds and museums hold “models for countless phenomena you will never witness, never touch or feel, and yet whose shape and behavior you can predict with stunning accuracy.” It’s amazing that as the Moon reflects on us, our minds reflect a moon. But I’m more interested in the dark.

I can imagine myself as a child in this curiously empty exhibit. First, I’d stand at about the same distance as the photographer and try to take it all in. (How nice that there’s nobody to get in the way!) Next, I’d run up as close as the guard would allow, examining each crag and crater above me. And then I’d start to wonder: what’s hiding in that dark corner? Why can’t I see the other side?

The scene brings back memories of the hemisperic Moon model in front of my hometown planetarium. On school trips, my classmates and I were always scheming to climb on top or crawl under when our teacher was distracted. The moon in my brain wasn’t so complicated then, and I wondered what it was like on the inside and where I could find the other half. Sure, I knew the thing on the lawn was just a model. But the thing in my mind couldn’t yet account for not knowing, for the idea that maybe there was no other half.

This is the truly astonishing thing about the Moon: for thousands and thousands of years, we never saw the other half. At the time my Moon model was made—sometime, I think, in the 60s—we still hadn’t modeled the far side! This grainy composite from the Soviet Luna 3 probe was the very first glimpse, sent back in 1959:

Of course, the other half was there in the models (and thus, in the brains). No one was surprised to find that the far side of the Moon looked very much like the near one. Even the earliest astronomers assumed the Moon was some sort of sphere. But the magnitude of our not-knowing, the undiscovered geography on the other side of our models, has always been as staggering as their complexity. Consider the Moon map.

Below is the first Moon map, Knowth Orthostat 47, a Neolithic rock carving in Ireland around 5,000 years old. It’s a fascinating image—the first sign of a model, a piece of knowledge, that would continue to grow in complexity and explain ever more. It is our capacity to encode the model, to take it out of our mind and smudge it on a cave wall, that makes the growth of knowledge and the evolution of our models possible.

The map hadn’t changed much when Leonardo Da Vinci made this moon sketch around 1505:

But the model had. By the 5th century BC, astronomers grasped moon mechanics and lunar cycles, culminating in Ptolemy’s 2nd century theory of lunar motion. (The Umayyad astronomers would clean it up in the 14th century, followed by Copernicus, Kepler, Tycho, and Newton). By the end of the 5th century AD, our moon models had a theory of reflected light.

Galileo was one of the first to glimpse a sliver of the far side, but through a glass, darkly, during lunar librations, when a bit of the edge was briefly visible through his telescope. Here are his moon sketches from around 1610:

Dutch astronomer Michael van Langren made the first real selenographic map in 1645 (Compare with a famous, roughly contemporary map of the Earth):

The complexity of our Moon models—our knowledge—has accelerated ever since. The latest moon-modeler, NASA’s Lunar Reconnaissance Orbiter, sent back 192 terabytes of data, resulting in this beautiful map:

I gaze at this moon, and think of how lucky we are to smudge our models on a cave wall somewhere outside our minds. (The moon in my brain now has two sides covered in craters, might even account for some not-knowing, but it doesn’t come close to terabytes of detail!) The Moon is so, so close—merely a few hundred thousand miles from the mote of dust trying to make sense of it. The quasars Deutsch describes are billions of light years away. And yet for five thousand years, half of it was blank, unmodeled, out of reach of our minds.

We have cultivated so much knowledge with science, built complicated and elegant and awe-inspiring models, and yet knowledge is still so fragile and circumscribed, so primitive and childlike—and the most precious thing we have. The things we see in the light are clear and bright and wonderful. But what humbles and awes me, as always, is stopping for a moment and staring into the dark.

TL;DR: This is the best model of the Moon. You are an astronomer in a doofy hat.