Everything about stars

The Sun is a star seen close up: a ball of glowing gas, layered like an onion, with a furnace in the middle.

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A star is a ball of gas heavy enough to light its own fire. How heavy it is decides almost everything else about it.

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The Sun turns matter into light in its core. The light then takes many thousands of years to find its way out.

A star's colour tells you how hot it is, and its true brightness tells you how big. Plot one against the other and the stars fall into order.

Spread a star's light into a rainbow and it is crossed by dark lines. They tell you what the star is made of, how hot it is and how it is moving.

Why astronomers keep four different rulers, and when each one is used.

The stars next door are light years away, and most are small red ones too faint to see. The bright stars of the night sky are the unusual ones.

Most stars are small, cool and red, and too faint to see without a telescope. They will still be shining when every star you can see tonight has gone out.

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Too heavy to be planets and too light to shine as stars, brown dwarfs glow faintly with leftover heat and slowly go dark. Our galaxy may hold tens of billions.

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A few thousand stars are bright enough to see by eye. All belong to our galaxy, most lie within 1,000 light years, and the patterns they make are only patterns.

Many stars come in pairs, threes or more, circling one another. Their orbits are the only direct way to weigh a star.

Some stars swell and shrink, some are hidden by a partner every few days, and in 2019 one of the brightest in the sky faded for months.

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Stars are born in groups. Some groups drift apart within the galaxy's disc, and some are tight balls of very old stars that have held together for most of the age of the universe.

A nebula is a cloud of gas and dust between the stars. Some are where stars are being born, and others are what dying stars leave behind.

Stars form in clouds of gas, shine steadily for most of their lives, and end as white dwarfs or in explosions, depending on their mass.

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A star near the end of its life swells to a size that is hard to believe. The biggest would swallow the inner planets whole, yet are thinner than the air you breathe.

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A supernova is a star blowing up. There are two ways it can happen, and for a few weeks one can outshine a whole galaxy.

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A white dwarf is the core a star like the Sun leaves behind: the mass of a star in a ball the size of the Earth, with no fuel left, slowly cooling.

When a massive star dies, its core can be crushed into a ball the size of a city with more mass than the Sun. Some sweep beams past us like lighthouses.

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A black hole is what is left when gravity wins completely. We cannot see one, but we can see what it does to everything near it.

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The first minutes of the universe made hydrogen and helium. Almost every other kind of atom, in the Earth and in you, was made by a star.

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Some stars brighten and fade on a steady beat, and the beat gives away how bright they truly are. That is how the distances to other galaxies were first measured.