Now I'm just a poor country astrophysicist. I grew up in the vast cornfields of the Midwest,

and now I live in the vast cornfields of the Midwest. But when I was 16, my dad took me on a special trip.

He took me to New York City.

And the country bumpkin that I was, I gawked at everything.

There was just so much stuff.

So much stuff and people and things and noises and you could hardly move your elbows and

there are weird smells and there is just activity it was like being in the middle of a beehive

it was almost overwhelming it was just it was just busy that was the thing that struck me

the most of my first visit to a big city,

like New York City. I'm pretty sure New York City qualifies as a big city is what struck me the most.

It was just busy. And years and years later, I did the whole astrophysics and cosmology thing.

I eventually ended up learning about galaxy clusters.

Not to be confused with globular clusters or stellar clusters, those are different episodes

to feel free to ask. I'm talking about galaxy clusters, clusters of galaxies. And when I learned

about galaxy clusters, the very first thing I thought of was cities.

So the last episode, or a couple episodes ago, was all about voids, which are basically the great Midwestern cord fields of the cosmos.

And today, it's about galaxy clusters, the bustling cities of the universe.

And like the voids episode, this will be a grab bag, exploring all sorts of neat

odds and ends and corners and crevices.

Thanks to at David the pawn on Twitter, 185 Transformer on YouTube, Andressee on email,

Felipe S on YouTube, Grace M on email, at Pete Burkett on Twitter, Dean, email, and Martin N on Facebook. Thanks to all

you, we're all going to visit the big city. And we're going to start with just the definition

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