Microwaves are from about 1 millimeter (about the size of a sharp pencil point) to about 1 foot long.

This window shows us the microwave energy known as the cosmic background radiation. It is the "noise" left from shortly after the Big Bang that began the universe billions of years ago. The different colors represent very tiny differences in energy that eventually resulted in matter clumping together into galaxies and even bigger structures throughout the universe.

This information was gathered by the Cosmic Background Explorer spacecraft over 4 years in the early 1990's.