95% of the universe is dark matter and energy.
Why it is true
Everything we know and see constitutes only 5% of the universe; the rest is invisible and remains a mystery.
Source: Cosmology
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.
Related facts
Space
A solar flare equals a billion hydrogen bombs.
Space
There are more stars in the universe than grains of sand on all the beaches on Earth.
Space
Fast radio bursts are cosmic signals that last milliseconds.
Space
There is a massive water vapor cloud around a quasar that holds 140 trillion times the water in Earth's oceans.
