(gentle music) - For thousands of years, humanity has been trying to make sense of their place in the universe.

- It's like we're Galileo again.

- They call themselves amateur astronomers.

They're a collection of volunteer hobbyists who spend their time looking for celestial objects in the night sky.

- This telescope is a 10-inch Newtonian-style telescope, and the mirror gathers the light from whatever we're looking at.

It's gonna be Saturn tonight, maybe, or a galaxy.

- And they come with gear many of us with just binoculars would envy.

One of their favorite things to do is host star parties.

- Seeing it in like 3D.

- To give the public a chance to see up close the sky as it is and learn a bit about how it all fits together.

- Comets fascinated me at an early age, and when Halley's Comet came around in the '80s, I really got the bug then and started trying to photograph things in the sky.

- Just looking at all the treasures that are up in the sky.

You got galaxies and nebulas, and yeah, you can look at 'em in a book, but it's a lot more gratifying to look at it personally.

As people have said, well, why do you take pictures of galaxies and nebulas?

Yeah, it's fine that you can look into a book, but they're so much better when they're your pictures.

They're things that you looked at, and then you present to your friends and family to show 'em what's up there.

- I cannot see Jupiter 'cause I see Saturn.

- So as the star party gets going, it's time to ask just how important are these amateur astronomers to the study of the cosmos?

- We depend critically on amateurs.

- Since only about 1/8 of the night sky has actually been mapped, scientists say these so-called amateurs play a crucial role in discovery.

By the numbers, amateurs have discovered hundreds of comets in the night sky, including the famous Hale-Bopp in 1995.

They're also credited for discovering between 20 and 30 exoplanets over the years, highlighting their role in modern astrophysics.

- I want the simplest telescope possible.

- Brand Fortner is an expert in looking back in time.

- One, two, three, four, five.

- How humankind first began how to decipher our place in the stars.

- They've got this humongous telescope.

- So let's rewind a bit, around 2,000 years to these ancient observers.

(upbeat music) So the Babylonians were superb with mathematics and they were superb with figuring out the positions and the motions of the sun and the moon, and especially the planets, which had a very complex motion.

They were able to predict lunar eclipses.

They were able to show that the Earth's spin axis precesses.

They were just geniuses.

But their interest was not modern.

Their interest was prediction.

They really could care less what the cosmos really was.

- So these ancient observers did just that, observed.

But their predictions help with things like harvest and crop schedules.

- Every culture has stories about the night sky.

That's where the gods are.

These are the shapes of the gods and they tell stories about that.

And then let's skip forward 1,500 years.

(ethereal music) - But there was still very little interest in what the universe really was.

- And that really didn't happen until Galileo.

He was the first one to connect evidence, observations, with the newly created telescope, with potential theories of the cosmos, that the planets are really like this.

The sun is really like this.

- Galileo worked in a period where everyone knew that Copernicus had theorized that the sun was at the center of the solar system and planets orbited around it.

It was called the heliocentric theory.

But in a twist, Copernicus said he didn't actually believe his own theory at the time, mostly because he didn't want to irritate the Catholic Church, which held that at that time, all things revolved around the Earth.

- He thought that he was making mathematical tricks to make the calculations easier.

And again, what you see is, until Galileo, there was this split between doing calculations and what is the universe really.

And Copernicus was one who just wanted to make calculations easier.

Copernicus did not believe in the Copernican theory.

- The theory until now was that planets orbited in circles.

Galileo and others, including Kepler and Tycho Brahe, liked the theory, but mathematically, it didn't work very well.

- It wasn't until the late 17th century that things changed.

His name was Isaac Newton.

Newton introduced a unifying theory of gravity, but how did he do it?

He invented calculus, and it showed that all objects attract each other and that the force depended on mass.

- And that single equation explained everything.

And so when we reach Isaac Newton, what we have is, for the first time, we understand what the universe is.

The universe doesn't really consist of things.

It consists of forces that are quantified by equations.

The universe is mathematical at a fundamental level.

This was an incredible philosophical change.

- You look into Pluto and you can never tell which one's Pluto and which one's a star.

So are these guys amateurs or philosophers?

Fortner says amateurs pick up the slack from professionals and organizations that simply don't have the resources or time to see it all.

- The amateurs know how to operate smaller telescopes.

Amateurs around me, they're looking at the night sky all the time.

They find stuff that we don't.

Our knowledge of our ignorance has exploded in the last 25 years, has exploded.

The sky is big, and the sky is ever-changing, and we need as many eyes as possible out there.

(gentle music)