Light energy travels in waves, but not all the waves are the same. The kind of light our eyes can see is only a tiny part of the energy that exists in the universe. Other kinds of energy are invisible, like the energy that makes our hands feel warm when we hold them over a fire, or the energy that cooks our food in the microwave. When Earth absorbs sunlight, it heats up. The heat, or "outgoing longwave radiation," radiates back into space. Satellites measure this radiation as it leaves the top of Earth's atmosphere. The hotter a place is, the more energy it radiates.
These data currently include daily composites from July 2006 to present.
