Daniel was looking at the stars and started wondering where they actually came from.

The answer starts in the dark, with clouds of gas.

And it ends with the iron in his blood.

Stars form when enormous clouds of hydrogen and helium collapse under gravity, heat up, and ignite nuclear fusion. That is the moment a star is born. Our sun formed this way about four and a half billion years ago -- and the leftover material became the planets, including Earth.

But the deeper story is what stars do while they live, and what they leave behind when they die.

What you will find in this episode:

• How gravity turns a cloud of gas into a star
• What nuclear fusion actually is and why it makes a star shine
• What happens when a star runs out of fuel -- and why it depends on the star's size
• How earlier ge ...