Hey, it's Lindsay. And it's also Marshall.
Hi. Hello. Hello. So, y'all, this summer we're trying out a lot of new ideas for the podcast, and we just came up with a new one.
We usually share stories of scientists making discoveries, but what if we shared your stories of science discoveries?
We were thinking about it because we have gotten so many great emails and recordings over the years from listeners who've gotten inspired by scientists they hear on Tumble to do their own science in their own experiments.
So if you listen to our mailbag episode we did this summer, you heard our listener Zoe describe her ingenious experiment on a patch of four-leaf clover she found in her yard.
Yeah, I mean, it's seriously an amazing experiment.
She did a great job and actually confirmed results that scientists seem to be finding on a mystery that they don't know the answer to.
So it's pretty amazing. Yeah, we're still blown away.
Yeah, like, go Zoe, seriously. But anyway, we want to know, have you done your own experiment?
And if so, tell us. Yeah, so here's how to tell us.
With the help of an adult, make a video or voice recording in a quiet place so that we can hear you clearly.
Yeah, like ideally not at a marching band performance or rehearsal.
When you go to a circus, that is not the time to make this recording.
Exactly. So on this recording, please tell us your first name and age.
What made you curious to do your experiment?
Describe your experiment and tell us what you found.
Or if you didn't find anything at all, how that made you feel.
Or you can tell us both your feelings and what you did because science doesn't separate one from the other.
Sure. So send us your recordings to tumblepodcast at gmail.com by Monday, August 18th.
2025. Yeah, if you're listening to this in 2026, it's too late.
It's too late. But I wanted to say that if you miss the deadline, you can still send them because we love to hear about your experiments.
And who knows, maybe we'll make this a regular feature if it works out.
Yeah, that'd be great. So anyway, let's get on to today's episode about an early astronomer who made a big discovery with just pencil, paper, and photography.
It's how big is the universe? Let's hear it.
Hi, I'm Lindsay. And I'm Marshall. Welcome to Tumble, the show where we explore stories of science discovery.
Today, we're talking about a woman who changed the way we think about the universe forever.
How could somebody change the way we think about the universe?
By finding out how big it is. Oh. In the mid-19th century, astronomers couldn't measure distance in space until Henrietta Leavitt showed them how.
We're telling her story with help from a modern-day astronomer.
Not many people know the name Henrietta Leavitt.
She lived over 100 years ago and not much is known about her life.
But we do know that Henrietta Leavitt changed the way astronomers see the stars and that her story is an important one.
I think Henrietta Leavitt's story is a story of persistence against the odds.
That's Karen Masters. She's an astronomer.
And if not for Henrietta Leavitt, Karen would have a much harder time with her own research studying galaxies.
So every time I'm doing something about the physical size of a galaxy, like how far across it is in light years, there is buried in that the Leavitt Law.
So what's the Levitt Law? It's a law like Newton's laws of gravity or Einstein's field equations.
So it's like kind of a big deal, but why haven't I heard of Henrietta Levitt before?
Well, Henrietta wasn't the type of person that people expected to do important science.
She lived during a time when very few women had jobs, and they definitely didn't have the same opportunities in science that men did.
So people used to think that women weren't as smart as men.
And when Henrietta Leavitt was a child, that was definitely a thing.
Not a true thing, though. Fortunately, Henrietta's family thought differently than most people at the time.
Henrietta Leavitt's family were educated.
Her father was a pastor and they believed in education for women.
So she was lucky in that they supported her to go to college.
After she graduated, Henrietta started looking for a job in astronomy, and she found one at Harvard.
So at the time, the astronomer who was running the Harvard College Observatory needed lots of people to look at photographic plates.
So what are photographic plates? Are they like dinner plates with photos on them?
Close. They were plates of glass that astronomers used to capture light from telescopes.
They created the first pictures of the stars.
A big innovation in astronomy at the time Henrietta Leavitt was working was the use of photography.
It was a huge revolution because it meant you didn't need to be sitting at the telescope in the middle of the night in the cold looking at the stars to catalogue them.
You could. Have people take these pictures and then you could send the pictures to be analyzed elsewhere.
So before this, you just have to be sitting at a telescope to study the stars, which I'm sure would get you a crink in your neck.
Neck pain or not, having photographs opened up astronomy to more people, especially women.
The astronomers who built the telescopes were mostly men, and sometimes they weren't very willing to share with the women who were interested in astronomy.
And so there were not very many women who had access to a telescope.
But the astronomer in charge of the Harvard College Observatory decided to hire women to look at these photographic plates.
He might have recognized that women were as smart as men and in need of jobs, but they also came at a lower cost.
So I have heard that it was because he could pay them less.
So you could get more brainpower for less money if you hired women.
Henrietta Leavitt made 30 cents an hour.
That seems like pretty cheap for an astronomer.
Well, Henrietta wasn't officially an astronomer.
She and the other women were called computers, which meant that they made computations, or mathematical calculations.
So she was a computer, like in the same way that we're podcasters before robots take over for us.
Exactly. Henrietta did things that computers do very quickly today, but she did them all by hand.
So she would have figured out what the coordinates were of the image she was looking at, and then marking down the position of each star, and also how bright it was.
Why would they want to know how bright the stars were?
Astronomers knew that a star's brightness told us something about where it is in space.
So brightness and distance are connected.
Exactly. So this is a bit like if you've ever been driving down a road at night and there's the headlights of the cars coming towards you.
When they're very close to you, they're sort of glaring in your eyes and you can't, you know, you can barely see they're so bright.
When they're far away, they're much dimmer.
So the exact same thing happens with stars.
If stars are closer to us, they appear brighter on the sky.
And if they're further away, they appear dimmer.
Henrietta's job was to create big charts of information about brightness in the location of the stars she saw on the plates.
She classified them into different types of stars.
Her co-workers took notice that one type of star seemed to steal Henrietta's attention.
I think they called her a variable star fiend, meaning someone who was really, really, really into variable stars.
A variable star fiend? That was like the wackiest nicknames that they had back then.
Oh, Henrietta, you're such a variable star fiend.
Oh, just go for those variable stars wherever you can find them.
So what's a variable star? Is it a star that is very able?
It's a star that changes its brightness from night to night.
There are stars that change their brightness from night to night.
So when you say I'm constant as the stars, you mean like you change all the time?
Well, most stars are constant, but variable stars are special.
And Henrietta got really good at spotting them.
She'd probably have multiple images of the same bit of sky and look for stars that changed in brightness.
Okay, so she wasn't just looking at one picture of a star and then moving on.
She'd look at the same images of the same star on different nights, right?
Yes, and so she would compare how bright they appeared across different nights.
Eventually, she found 25 variable stars in one nearby cloud of stars.
For each of those stars, she worked out the period of it getting brighter and dimmer.
So a period like a cycle. Yes. When Henrietta would spot a variable star, she'd see it go bright, brighter, brightest, and then dim, dimmer, dimmest, and back again.
Variable stars didn't do this at the same speed.
Some stars had a short and fast cycle, and others were long and slow cycles.
While Henrietta was writing this all down, she noticed something.
And she made this chart and she noticed this relationship, that there was actually quite a simple relationship, that the brighter the star is, the longer its period of variation is.
I want to take a little moment here to say it wasn't Henrietta's job to notice relationships or patterns in the stars.
She was getting paid very little just to enter data from photographs.
But what she did was incredibly valuable.
She discovered the missing piece of a puzzle that astronomers had been struggling to find for years.
What puzzle was that? Remember back at the very beginning of the episode, I said that astronomers didn't have a way to measure distance in space?
Yeah. So to know how far a star is from Earth, Astronomers needed to know how bright stars actually were.
Henrietta used these variable stars to figure out a star's true brightness.
And with that, astronomers could finally figure out its distance from us.
So the star was like a measuring stick that they'd never had before.
Exactly. She provided the method by which other people could measure the distances to other galaxies.
That method is called the Leavitt Law. It gave other astronomers a massive shortcut.
They didn't need to do all the work of making charts like Henrietta did.
They just had to find a variable star and then plug in her equation.
So Henrietta really knocked her computer job out of the park or like out of the galaxy and into the next one.
And the one after that. And it goes on forever.
Absolutely. Henrietta's boss published her findings in an astronomy journal, but under his name.
And sadly, Henrietta died only about 10 years after that.
But her story was far from over because her work would go on to help make a discovery that would rearrange our picture of the universe forever.
And we'll hear all about that after this quick break.
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We're back. So at the time that Henrietta was alive, the big debate in astronomy was whether the universe was entirely made up by our own galaxy, the Milky Way, or whether there was more universe outside of it.
I guess there always has to be a point where people figure stuff out.
But I mean, I figured we always knew that there were galaxies outside the Milky Way.
Yeah. And like our galaxy was one of many.
Yeah. But no. No. The very idea of galaxies outside the Milky Way was beyond their comprehension.
So at the time, they were like, oh, my God, the galaxy is so big.
There can't be anything outside it. That's ridiculous.
I mean, and that literally was part of the scientific debate at the time was there just can't possibly be anything outside the galaxy.
It can't possibly be that big. There's such a thing as too big, and that's just too big.
That was astronomers' gut reaction, and they didn't really have more to go on than that.
But around 1920, just after Henrietta's death, one ambitious astronomer picked up on her work.
He was trying to answer this question by studying objects in space called spiral nebulae.
And his name was Edwin Hubble. So Edwin Hubble was very interested in figuring out this puzzle of what the spiral nebulae were, whether they were things inside our galaxy or things like our galaxy much further away.
So how did he think spiral nebulae would help us find out how big the universe is?
Well, if Hubble could find a variable star in a spiral nebula, he could figure out its distance from Earth.
He chose Andromeda, which was one of the closer ones.
And with Henrietta's equation, Hubble found Andromeda's distance from Earth.
And Hubble comes along and points out, well, actually, Andromeda is really, really far away.
Like, multiple times as big as the galaxy far away.
So he's like, guys, believe it. The universe is more than just the Milky Way.
And, like, it's a lot more. Yeah. Yeah. It's bigger than too big.
Most astronomers had thought Andromeda was part of our own galaxy, but Hubble proved that it was so far away, it was outside the Milky Way, meaning that the universe is indeed mind-bogglingly huge.
Space is really, really big. It's really hard to get your head around how big space is.
So this is a huge shift, like knowing that the Earth isn't flat and also that it goes around the sun and also that it's like actually tiny compared to the sun and also the sun is tiny compared to the galaxy and the galaxy is tiny compared to the universe.
And it just goes on like that. Understanding distances in space changed how we thought about the universe forever.
And the bigness of it is still mind boggling, even to the people who study space.
I get a bit scared sometimes because it's so big.
I'm like, this is ridiculous. My galaxies in my head when I'm studying them are about this size, about the size of a dinner plate.
I think it really says something about how big and vast space is that the people who spend their most time looking at how big it is and know it the best still aren't really okay with it.
Karen told me she has to actively not think about how big the galaxies are that she's studying in order not to be paralyzed by awe and wonder all day.
Can't just walk around going, wow, all day.
Yeah, it's like, hey, Dr. Masters, we need you to order your coffee now.
There's a hundred people behind you in line and you've been standing there for 10 minutes.
Just thinking about the size of the universe, size of galaxies.
It's crazy. I imagine it would be a problem for astronomers.
It does seem truly impossible to wrap our heads around the size of the universe.
Our own galaxy is 100,000 light-years wide.
That's 588 quadrillion miles, or 946 quadrillion kilometers.
Oh my gosh. So quadrillion would be what?
A thousand trillion and a trillion is a thousand billion and a billion is a thousand million?
While we're on large numbers, astronomers estimate that there's about 200 billion galaxies in our universe.
Oh my gosh. And we know, again, thanks to Hubble, who is using Levitt's law, that the universe is expanding.
So the universe is actually unimaginably bigger than our Milky Way, and Henrietta set the stage for understanding all of that.
Yes. She went so far beyond what was expected for her as this lowly computer in an observatory.
But for Karen, it's not surprising that Henrietta could do what she did.
Karen can actually relate to it. People often, when they hear I'm an astrophysicist, say, oh, you must be really smart.
But I think it's really more about my interest and my persistence that has meant that I've succeeded.
I just found it fascinating and I kept studying it until I became one of the world's experts in it.
And I think Henrietta Leavitt, her story really shows that, right?
She thought variable stars were fascinating.
And as a result, she discovered something that changed how we understand the entire universe.
When it comes down to it, Henrietta was just a variable star fiend.
Indeed she was. Would you like a spot of tea?
Oh, I'm too busy fiending on the variable stars.
Oh, Henrietta. You can be a star fiend too, just like Henrietta, or really any kind of science fiend you want to be.
Galaxy Zoo is a citizen science project that Karen Masters helped start.
On it, you can help scientists identify objects in the sky through digital images and contribute to real scientific research.
We'll guide you towards using it as part of our free series, Cataloging the Universe, which you can find on our website, sciencepodcastforkids.com.
Thanks to Dr. Karen Masters, Professor of Astronomy and Physics at Haverford College.
And special thanks to Dinesh Krishnarow, Assistant Professor of Physics at Colorado College.
Learn more about Henrietta Leavitt's impact on astronomy on the bonus interview episode on our Patreon.
It's available to patrons who pledge just $1 or more a month on patreon.com slash tombopodcasts.
And you can find our free audio course, Cataloging the Universe, on sciencepodcastsforkids.com slash universe.
It's designed for both home and classroom learning, so go check it out.
Sarah Robertson Lentz edited this show and designed the episode art.
Elliot Hajjaj is our production assistant.
And Gary Calhoun James engineered and mixed this episode.
I'm Lindsay Patterson, and I wrote this episode.
And I'm Marshall Escamilla, and I made all the music and the sound design for this episode.
Tumble is a production of Tumble Media. Thanks for listening, and stay tuned for more stories of science discovery.
All right, everybody. Thanks so much for listening to that awesome episode.
It's really a great one in my personal opinion, though I did help make it.
So I don't know if I get to have an opinion, but anyway, it's one of my favorites of all time that we've ever done.
So I hope you enjoyed it too. But anyway, here we are at the end of the episode.
And that means that it's time to do our Patreon people.
Thank you. Patreon people. Yay. We got kind of a lot of birthdays to shout out to, and I also want to give some recognition to the new Patreon supporters we have, Alexa, Soren, Leland, and Colton.
Thanks, y'all, for your support. It means a whole lot.
And now on to the birthdays. A happy birthday to Rye on August 10th.
Mom and dad are so proud of you and love you very much.
To Zosia, happy birthday on August 12th.
Grandma and Bumpa hope you hear this birthday shout out and know how much you are loved.
That's very sweet. Thanks, Grandma and Bumpa.
To Jonathan, mom and dad love watching you discover the world through scientific exploration, which is the best way to discover the world.
Stay curious and creative. They love you very much.
And a happy 10th birthday to Charlotte. Keep asking questions and learning about the world around you with lots of love from Mommy.
And also, what I hope is still your very favorite science podcast for kids.
A happy birthday on August 16th to Sam. Mom and Dad love you so much.
A very happy August 16th birthday as well to Sophia.
Mom, Daddy, and Cora love you to the moon and back.
A happy birthday on August 17th to Marie.
Mom and dad love you. You have such a curious mind and are so observant.
It's no wonder you love science. To Mackenzie, daddy and mommy love you so much.
Keep learning and stay curious and have a great birthday on August 18th.
Aiden, everyone loves all your questions about the planets, the stars, and the universe.
Don't ever stop asking questions. A happy birthday on August 19th from mommy, daddy, sissy, and Henry.
They all love you. To Colton, Mom and Kaya love you and your big curious mind and hope you have a happy birthday on August 19th.
Thanks to all of you and to everyone who supports Tumble on Patreon.
If you want to get a birthday shout-out of your own like these fine folks, simply support Tumble on Patreon at the $5 level or higher by going to patreon.com slash tumblepodcast.
Or if you're on Spotify, just tap the subscribe button and it'll give you access to our subscriber feed and birthday shout-outs.
I'd also like to remind everybody about our Science Songs album, which you can stream wherever you get your music, and to any of you who are still hanging around.
I want to let you know that I've created a crossword puzzle to go with this episode.
You can find it at bit.ly slash universepuzzle.
And go try it out. If you send me a screenshot of a completed version of the crossword puzzle, it would just make me so happy.
And I will email you back and maybe send you a special present.
You never know what you might get. Anyway, we'll see you next time.
