It's a map of the solar system.

Recently I got really curious and I started zooming out, well past the solar system and deep into the night sky, and this kind of blew my mind.

We have mapped these stars that are so far away from us, light years away, and yet here they are on this map, somehow positioned in space.

This seems impossible to me.

How is it that we're able to, from this little speck of dust, look up and somehow gauge how far away things are?

Like this one specific star, how do we know that this is 864.3 light years away?

I mean that's like 8 quadrillion kilometers, it's insanely far.

The story of how we did this, how we measured the distance to these incredibly far away objects in the sky, it's a story of people looking up and asking questions, and in the process creating a map of the heavens.

In the old days, people knew about the planets, but they thought the stars were in some sort of vault of heaven just a bit further away than the planets.

So mapping the night sky, this is a big topic.

Let's start small first, the stuff close to us.

How do we know how far Jupiter is, and the moon, and all of that?

From here, the methods get trippier and trippier the further away you get, but for now, the solar system.

Measuring the distance to planets is relatively easy because we see the planets move.

We see them spin around the sun, and we can observe their behavior over the course of decades and generations and record that.

After a lot of observation, we realize that the planets go around the sun, and they go in this kind of elliptical shape.

They don't go like in a perfect circle.

You can then observe that the planets start moving quicker the closer they are to the sun because of gravity.

Gravity pulls it in and whips it around.

Observing the planets and how they move around the sun allowed one very smart German astronomer, who apparently exclusively ate with chopsticks.

I'm kidding.

I know they're not chopsticks.

Okay?

It's just a joke.

It's actually just like a compass.

Ha ha ha.

Anyway, this guy, Johannes Kepler, used his chopsticks to measure all of this movement, how the planets moved.

He plotted it, and he came up with some really savvy equations, and ratios, and laws that gave us the average distance to each planet.

Suddenly, the night sky went from 2D to 3D for the first time.

Which gave us a place, a physical place, relative to all these planets floating around the sun.

Okay, but this is child's play when it comes to measuring distances in space.

These planets are like our next door neighbors.

So now, let's step into the big leagues and talk about how we started to map stars and their distance from Earth.

For the stuff that's not orbiting the sun, that's really far away, we can use a concept called parallax.

Wait a minute.

Parallax?

Parallax sounds strangely familiar when talking about physics in space.

It's still scalary.

I mean, did we say that?

But he goes by the pseudonym parallax.

Got that great name.

Okay, no, no, no.

Not that parallax, the pseudoscientist from the 1800s.

I'm talking about the scientific concept.

Parallax is a concept that says that if you're observing something far away and you shift your position relative to that far away thing, the far away thing will look slightly different relative to the background.

Okay, so let's say we're looking up at the night sky and we want to know how far away this star is.

Remember that Earth is always floating around the sun at any given time, which is moving us in space.

So if we observe this star in May and then wait six months till November and observe that star again, we've now gained a new perspective on the star and what it looks like relative to its background.

This gives us an angle that we can use to calculate this distance.

What we don't know is this value.

This is the distance.

This is what we're looking for.

But we do know a few things.

We know this distance because it's just the distance from Earth to the sun, which happens to be 149 million kilometers or one astronomical unit.

This distance times two.

And then we also know this angle up here because we measured it from two different perspectives.

Thanks to the wizardry that is trigonometry, we can use this distance and this angle to determine what this distance is.

This works really well and it's allowed us to measure the distance to a lot of stars.

But remember that a key ingredient to this whole parallax thing is the slight shift in perspective between the first angle and the second angle.

As you start to measure things that are further and further away, this angle becomes slighter and slighter until eventually it becomes impossible to discern.

It's so minuscule, the perspective shift, that you can't actually detect it.

So there's a limit to how far parallax goes.

With our Earth-based telescopes, we've been able to perceive the angle enough to where we can see things that are about 300 light years away.

I mean, that is way bigger than like the things that are close to us in the solar system, but it's still a tiny number compared to like the galaxy or the universe.

Luckily, we have fancier tools like this guy that have really good technology for detecting these slight angle differences from two different perspectives of a star.

And that's allowed us to observe and measure the distance to stars that are up to 3,000 light years away, way further out.

Okay, so here's where we're at.

With Kepler's fancy equations, watching the planets move around the sun, we've been able to measure the distance to planets.

With parallax, we've been able to measure the distance to stars that are really far away and get a 3D map of our galactic neighbors.

But we're still not really scratching the surface of the distances that exist in the universe.

So how do we do that?

This is where it starts to get kind of crazy and trippy and weird.

And I'm going to do my best to explain this in a way that comes through.

So here we go.

One of the major methods for measuring the distance to super far away stars and galaxies was pioneered by a computer at Harvard in 1912.

Wait, what? A computer in 1912?

Yeah, that's what I said. A computer at Harvard in 1912.

But computers weren't invented until the 1950s.

But computers in 1912 looked like this.

This is a group of women who worked in Harvard's astronomy department in the early 1900s.

Their job title was literally computers, meaning someone who executes predetermined logical calculations on large inputs of data.

Harvard astronomers were taking loads of photos of the night sky with their new fancy telescopes.

The images came out like this.

Glass plates with photos of the night sky developed on them.

The computers were tasked with looking at each of these plates and naming and classifying the stars by their brightness and their type.

They were basically creating a 2D map of the sky.

They didn't know how far away they were, they just were classifying their position in the night sky relative to our perspective on Earth.

At the time, a lot of legit astronomers figured that what was in our galaxy was all there was to the universe.

We had no idea of knowing how far away some of these objects were, so we just figured that maybe everything is somewhat close by in our galaxy.

One of these computers was named Henrietta.

She was assigned to focus on one big cluster of stars in the night sky and to look at and classify those stars.

She documented thousands of stars but was bothered by this one question.

If you look up at the night sky and you see a super bright star, if you look up at the night sky and you see a super bright star, is it super bright because it's a big bright star or is it super bright because it's just close by?

By the same token, if you see a really dim star, does that mean it's just really really far away and it's actually a big star that's super bright or it's actually just a small dim star?

We really had no way of knowing because again they had no idea how far away these objects were that they were measuring.

She was looking at this one part of the night sky, this one cloud of stars.

She didn't know how far away that cloud was but she figured all the stars were about the same distance from Earth and she noticed that some of these stars were pulsating.

They were getting brighter and dimmer, brighter and dimmer and they were doing it at a strangely consistent rate.

If one of the stars took four days to get brighter and it took four days to get dimmer and four days to get brighter, it would stick to that pattern, that period over and over again.

Very reliable, very consistent.

You may be wondering what does this have to do with mapping the night sky?

We're getting there.

So Henrietta decides to make a graph to start to plot every one of these stars that are pulsating and determine if there's any sort of pattern.

On one axis she put how long it took for these stars cycle to go from bright to dim.

Maybe it was two days, maybe it was five days, maybe it was ten days.

Remember that each of these stars were showing a very consistent pattern of sticking to their cycle.

On the other axis she plotted how bright they were at each of these phases, at their dimmest and at their brightest point.

So you've got brightness on this side and you've got how long it takes for this pulsating to happen on this one.

So let's say she sees a star.

She sees that it takes two days for it to go from dim to bright and then two more days to go from bright to dim.

And then at its dimmest point its brightness value is down here and at its brightest point it's more like up here.

So this is what an entry would look like for one of these stars that she's observing.

She did this for a bunch of stars night after night and she started to see a pattern.

What this graph tells us is that stars that have a really long cycle going from dim to bright, let's say they take like ten or twenty days to do that, those stars are overall really bright.

They're probably big, they have more energy.

Whereas the opposite is true.

Stars that pulsate really quickly, that maybe just take a day or a half a day to go from dim to bright to dim to bright, those stars are actually overall much dimmer, potentially smaller, not actually as bright and intense as the stars that take a really long time to do their cycle.

So now if you look at the night sky and you see a really dim star, let's say, you don't know if it's dim because that's just a really small star or it's dim because it's really, really, really far away.

It's actually a super bright star but it's just super far away from our perspective so it looks dim.

But now with Henrietta's formula you could look at the pulsating of that star and if it's pulsating really slow, taking ten days to go from dim to bright and bright to dim, then you can be sure that that's actually a really big bright star that just looks dim to us because we're super far away from it.

This gave astronomers a yardstick that they just didn't have before to observe and understand the distance to stars that were way, way outside of the previous tools that we had to measure distance.

They took another swath of the cosmos and took them from 2D to 3D.

Soon after Henrietta Leavitt discovered this amazing relationship, a man by the name of Edwin Hubble, famous astronomer, decided that he wanted to use this to settle the grand debate on whether or not the galaxy was all there was to the universe.

He'd been looking up at the sky and been seeing this kind of fuzzy cluster of stars that he didn't really understand. Was it close? Was it far away?

Hubble was able to pick out one of the stars in this cluster and look at how it pulsated.

Using Henrietta's formula, it became very clear to Hubble that this little fuzzy dot in the sky was very far away, way outside of our galaxy.

This settled the debate about whether or not our galaxy was the entire universe or not.

That little fuzzy spot in the sky that Hubble was looking at turned out to be the Andromeda Galaxy.

It was a groundbreaking discovery, all made possible because of Henrietta Leavitt's formula.

And at the time, Hubble estimated that it was probably around 700,000 light-years away.

We've since honed that estimate to more like 2.5 million light-years away.

And now, using the telescope that bears Hubble's name, we've been able to observe that there aren't just a few galaxies outside of our own, but billions.

Okay, that's it. That's the answer to my question.

That's how I'm able to zoom around the solar system and the galaxy using this computer program.

The methods I talked about here are kind of the main building blocks of measuring distance in space.

We're continuing to push the bounds on this.

There are now methods for measuring the distance to all sorts of types of galaxies, all sorts of types of distances, and we continue to build out a map of the night sky in 3D.

And I'm really grateful for that.

Honestly, I'm grateful for the pioneers who put their minds to giving us perspective because it allows me to see where I live in the cosmos and what kind of space I occupy in the night sky.

And for some reason, that perspective, knowing where the stars are and knowing how far away they are, just kind of has ingrained itself into my mind and allowed me to keep perspective as I live my day-to-day life.

Anyway, that's that. Thanks for watching.

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