First look
The idea, in plain words
Stars are not for ever. They are born, they shine for a very long time, and they die.
A star begins as a cold, dark cloud of gas and dust. Gravity pulls part of the cloud into a ball. The ball heats up as it shrinks, and when the middle is hot enough the star switches on.
Then, for most of its life, almost nothing changes. The Sun has shone steadily for about 4.6 billion years and is roughly half way through.
When the fuel in the middle runs low, a star swells into a giant. What happens next depends on its size. A star like the Sun puffs its outer layers gently away and leaves a small, hot ember. A heavy star blows itself apart.
Go deeper
That was the idea. The same subject is written again below for readers who want more, each on a page of its own.
Words used here
- Nebula
- A cloud of gas and dust in space. Some are where stars form and some are what dying stars throw off.
- Protostar
- A star in the making: a ball of gas still shrinking and heating up, before fusion has begun in its core.
- Main sequence
- The long, steady part of a star's life while it fuses hydrogen in its core.
- Red giant
- A star near the end of its life that has swollen to many times its old size and cooled to a red glow.
- White dwarf
- The hot, dense core left behind when a star like the Sun dies: about the size of the Earth, and no longer making energy.
- Supernova
- The explosion of a star. For a few weeks it can outshine a whole galaxy.
- Nuclear fusion
- The joining of light atomic nuclei into heavier ones, which releases energy.
Where this comes from
The words are written for this site. The pictures are drawn by the page from the figures in the lesson, and each one says underneath what it is based on.