If you go outside on a clear dark night and look at the sky, you might see a few thousand stars. Not a single one of them will be the most common type of star in the Universe. You won't see a red dwarf without a telescope.

1. About 75% of known stars are red dwarfs.
Astronomers estimate that three out of every four stars are red dwarfs.

2. Red dwarfs are the smallest stars in the Universe.
No one had ever seen a red dwarf before the telescope was invented. Even the brightest red dwarfs are just a tenth as bright as the Sun, and the smallest ones are only about 1/10,000 as bright.

3. The first person to discover a red dwarf was Nicolas-Louis de Lacaille.
Lacaille was an eighteenth-century astronomer who measured the positions of nearly ten thousand stars in the southern hemisphere. He also invented new constellations to fill spaces between the existing southern constellations. Lacaille discovered the two brightest red dwarfs that we know of.

4. The nearest red dwarf to the Solar System is Proxima Centauri.
Proxima Centauri is part of the triple Alpha Centauri star system, which is less than four and a half light years away in the constellation Centaurus. It was discovered by Scottish astronomer Robert Innes in 1915.

5. Red dwarfs shine because they're nuclear reactors.
Red dwarfs produce energy by hydrogen burning. This isn't like burning coal. It's a nuclear reaction called fusion. When nuclei of hydrogen get squeezed together to make helium, it produces energy. This is also how the Sun gets its energy.

6. The smallest red dwarf that's been measured is OGLE-TR-122B.
The tiny star OGLE-TR-122B is the smallest star whose size we know. Its mass is about 10% of the mass of the Sun. That's almost as small as a star could be and still be able able to fuse hydrogen. The star was discovered by the OGLE project run by Poland's Warsaw University Observatory.

7. Red dwarfs are red because they're cool.
The color of a star tells us its temperature. The Sun, a yellow dwarf, has a surface temperature of about 6000°C. Red dwarfs are the coolest stars. Their average surface temperatures are about 2000 - 4000°C. White stars are hotter than the Sun and the hottest stars are blue. In the same way, a blue flame is hotter than an orange one. White hot metal is hotter than red hot metal.

8. A star's lifetime depends on its mass, so red dwarfs will live almost forever.
Big stars have more mass than small stars. Even though they have more fuel, they don't burn longer. They just burn brighter and die young. Smaller stars are dimmer and last longer. The Sun is almost five billion years old, halfway through its lifetime of about ten billion years. Really massive stars may last only a million years. The smallest red dwarfs could live for trillions of years.

9. When all the other stars are burned out, the red dwarfs will still be shining.
When a star finally runs out of fuel, nuclear fusion stops. All that's left is some kind of dead, shrunken remnant. However there aren't any red dwarf remnants yet, because the Universe is less than fourteen billion years old. All of the red dwarfs that ever existed are still shining. They will still be shining when the Universe is over seventy times as old as it is now.

10. There are planets orbiting red dwarfs.
Astronomers have discovered planets around red dwarf stars, and they seem to be common. Many are probably Earth-sized planets. In 2014, astronomers found that Kapteyn's Star has two low mass planets in its habitable zone. The habitable zone is the area around a star where water could be liquid. The habitable zone of a red dwarf star is close to the star, and astronomers are trying to work out what this could mean for the possibilities of life there.