365daysDate: May 29, 2009

Title: Dear Lyla, This is where you came from


Podcaster: Lyla’s Uncle Johnny

Organization: None

Description: May 29th will be my niece’s 1st birthday. I’ll write/read her a “letter” explaining where the heavier elements in her body came from, explaining how they were created millions of years ago in supernova explosions billions of miles away; I want to convey to her the incredible beauty of the true origins of life.

Bio: I’m 32, from the North East of England but live in Melbourne, Australia. Science, and astronomy in particular, is my hobby/passion. I remember lying awake as a kid wondering what happened when you got to the edge of the universe; the hairs on the back of my neck stand on end when I think about it. I work in IT and when I’m not voraciously devouring science podcasts or books I’m out drinking in the sunshine.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Joseph Brimacombe.


Dear Lyla,

Happy first birthday, my beautiful niece. I wish I was there to share it with you, but I’m on the other side of the world – so I thought I’d send you a birthday story instead. For everyone else listening, if it’s your birthday – happy birthday too!

As you’re now one year old, I thought I’d tell you a little story about where you came from. There are lots of stories about where little girls came from, but I think this one is the most beautiful.

First, you need to know just a little bit about physics. This sort of physics relates to things that are very, very small. In fact, almost the smallest thing that it’s possible to be: it’s called an atom. And atoms make everything else; everything that you can see around you, everything that you can touch, including yourself, is made of atoms.

So what’s an atom? It’s pretty complicated, so we won’t go in to much detail, but the key thing to know is that there are different types of atoms, and what we call them, and how they behave, depends on the number of protons in the middle. An atom with 1 proton in the middle, which is the simplest one there is, is Hydrogen. An atom with 2 protons in the middle is Helium. Carbon and Oxygen, which together make up most of your body, have 6 and 8 protons.

Now, about 13.7 billion years ago the universe first came in to existence – hang on, what did I say? 13.7 billion years? Yeah, that’s right, the universe has been around for almost 14 billion years. That’s about 14 billion times longer than you have, so far. When the universe first came in to existence, the only atoms that existed were the very simple, or light atoms – it was mostly Hydrogen, with one proton in the middle, some Helium, with 2 protons in the middle, and a very tiny amount of the next atom, Lithium.

To make the heavier atoms, like Carbon and Oxygen, you need somewhere really, really hot. The very early universe was only hot enough for perhaps the first 20 seconds; that’s right, for the first 20 seconds of its 14 billion year life. So we need somewhere else.

This leads us on to another bit of physics: stars. Our sun is a star, and all of the light and heat that you see and feel coming from it is basically because it’s burning. It’s a special type of burning we call “nuclear fusion”.

Stars are made from the Hydrogen and Helium produced in the early universe; these lighter atoms are attracted together due to gravity – which we’ll talk about more a little later – and eventually the amount of gas is so great, and so heavy, that it basically sets fire to itself, and that’s what we call a star.

Stars live for millions of years, and over those millions of years what they do in the middle, in the very very hot, dense core, is burn the hydrogen; when this stuff burns, it’s is called nuclear fusion – because it’s not just burning, it actually squashes – fuses – the atoms together.

This is the cool thing about stars. Stars are the only place in the universe where the heavier stuff, like Carbon and Oxygen, with more than 1 or 2 protons in the middle, this is the only place that these atoms can be naturally made.

To make the heavier atoms we have to take the lighter atoms and squeeze them together really hard – really, really hard. It has to be very hot, and there has to be a lot of pressure, and when there is – like in the middle of a burning star – the protons from Hydrogen can be fused together; so now instead of 6 single Hydrogen atoms with 1 proton each, we have 1 atom with 6 protons – and we have Carbon!

And this is basically what happens in the middle of a star; over the millions of years of its life, the lighter atoms go through a special burning cycle and eventually become the heavier atoms, like Carbon, Oxygen, and Nitrogen.

This process carries on for millions of years. That’s what’s happening in our sun right now. Eventually the sun, just like any burning object, will run out of fuel; the star has reached the end of its life and what happens next depends on how heavy the star is.

Depending on just how heavy the star was, it can die and explode in a number of really cool ways. Some stars expand slowly, throwing off some of their atoms and starting another burning cycle with what’s left; our sun will die like this in about 4 billion years. What’s left after that is a diamond the size of the earth. Diamonds are just carbon, and that’s what our Sun will be when it finally dies.

Some stars – the really big ones – explode in a really spectacular way and we call these supernovae; every now and then we can see a new star in the sky as the massive energy released in the explosion shines across the universe. Some of these explosions are so bright, we can even see the new star during the day. There’s a really beautiful picture of a supernova taken by the Hubble Space Telescope, which I’ll link in the notes of this podcast. Get your mam to show you.

So the important thing to think about here is the stuff that these stars throw out when they explode is the carbon and the nitrogen and all of these heavier atoms that have been made in the centre of the star as they’ve been burning over millions and millions of years. This stuff gets thrown across the universe by the force of the explosion. There’s another great picture, again taken by Hubble, which I’ll also link to. It shows the expanding wave of debris created by a supernova explosion which happened about a thousand years ago.

Now, the universe is a very, very big place. Very, very big. So these atoms fly across the empty space of the universe for, probably millions of years. Until, one day, they come close to something – and when you get close to something in physics, that’s what we call gravitational attraction. Being close to something, like you being close to the Earth, means that it pulls you in towards it. The bigger the thing, the more pull it has. And this is what our solar system, the Earth and the sun and the other planets, does, eventually over the course of millions of years, to some of those exploded atoms that are flying through space.

Now, I’m condensing millions of years of time into ten minutes here, so you have to imagine the star has exploded, and all of the carbon and the oxygen and the other heavier atoms has been traveling across space for millions of years and some of it has eventually found itself near the Earth. Some of it falls to Earth, where it stays.

And then, for millions more years, it probably doesn’t do much at all. It just hangs around on Earth; maybe it’s part of the soil, maybe if it’s hydrogen or oxygen (which together make water) it’s part of the ocean.

Eventually, however. Eventually some of those atoms of carbon and oxygen, that were made in the centre of a very very distant and long dead star, they found their way into my beautiful baby niece Lyla. And when I touch you, when the fingers on my hand touch the fingers on yours, what’s actually happening is that the atoms of carbon that are in my body – the atoms that make me – are touching the atoms of carbon that make you.

But now we know where those atoms of carbon came from. The very atoms that I touch, that are in my body, that are in your body, they were made millions of years ago in the centre of a distant star, then they spent millions of years flying through very lonely, empty space, then they probably spent millions of years hanging round on Earth not doing much at all. But eventually – those atoms of carbon made … you.

And that’s where you’ve come from. That’s where the flesh and blood that is you first started. So when you look up into the night sky and you see little twinkling stars, just think, in millions and millions of years, the heavy atoms that are being made in the middle of those stars will eventually make their way to some other planet, and you never know; they might make somebody else. I doubt she’ll be much like you, but I hope someone is there one day to tell her this story; because I think this is a really beautiful story, and it’s a true story, and we can even watch it happening.

It’s amazing to think that we were born in the stars; we are literally star dust. If that’s not the most beautiful fairy-tale for a little girl there is, then I don’t know what is.

Happy birthday, Lyla. I’m sorry I wasn’t there to share it with you, but I’ll be there in a week – then hopefully I’ll tell you this story again, and we can sit under the stars and watch them for real. When you’re older I promise to teach you all about astronomy, because it’s really beautiful.

Until then, keep looking up into the sky. Just remember that you see the same stars that I see. I’ll be thinking of you.

Love, Uncle Johnny.

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at Until tomorrow…goodbye.