+Dave Cole will teach you science before you know you are even learning! Great Share. Thanks!
Astronomy term of the day Dark Matter

Dark matter is the term to describe unseen matter in the universe, because it doesn't emit any radiation. Also the calculated movement of galaxies, galaxy clusters and stars are faster than expected. As it is inferred to exist at this time, as there is no way to test for it. I'm sure there is speculation as to its composition.

Further reading.

Detecting Dark Matter
Minute Physics: What is Dark Matter?
Shared publicly