Understand that stars don't “burn” but shine thanks to nuclear fusion, and that a star's color tells you its temperature.
It's not a campfire
Where a star gets its energy
A star doesn't shine the way a campfire or a light bulb does. Nuclear fusion goes on in its core: under monstrous pressure and at temperatures of millions of degrees, hydrogen nuclei fuse (“bake together”) into helium. Each such fusion releases an enormous amount of energy — and that is what makes the star shine.
A star is a constant struggle between two forces. Gravity squeezes it toward the center with all its might. And the energy from the core pushes it outward. As long as these forces are balanced, the star is stable and shines steadily for billions of years.
In this way, our Sun fuses about 600 million metric tons of hydrogen every second. Its fuel will last about another 5 billion years — the Sun is right in the middle of its life now.
Lesson notes
Where a star gets its energy
A star doesn't shine the way a campfire or a light bulb does. Nuclear fusion goes on in its core: under monstrous pressure and at temperatures of millions of degrees, hydrogen nuclei fuse (“bake together”) into helium. Each such fusion releases an enormous amount of energy — and that is what makes the star shine.
A star is a constant struggle between two forces. Gravity squeezes it toward the center with all its might. And the energy from the core pushes it outward. As long as these forces are balanced, the star is stable and shines steadily for billions of years.
In this way, our Sun fuses about 600 million metric tons of hydrogen every second. Its fuel will last about another 5 billion years — the Sun is right in the middle of its life now.
A star's color tells you its temperature — and here we're in for a surprise that goes against everyday intuition.
In everyday life, “red” seems hot (a red button, a red chili pepper), and “blue” seems cold (the blue cold-water tap). With stars, it's the other way around!
— Red stars are the coolest (surface about 3,000 °C).
— Yellow ones, like our Sun, are in the middle (about 5,500 °C).
— Blue-white stars are the hottest (10,000 °C and much more).
You can easily see this on Earth too: a candle flame at the wick is reddish-orange at the top and bluish at the base, where it's hottest. The hotter an object, the “bluer” its glow.