Here's why:

* Shortwave radiation has a shorter wavelength, typically less than 4 micrometers. This means it carries more energy. Sunlight is made up of visible light, ultraviolet radiation, and some infrared radiation, all of which fall within the shortwave spectrum.

* Longwave radiation has a longer wavelength, typically greater than 4 micrometers. This radiation carries less energy and is often associated with heat emitted by the Earth.

So, while the Earth emits longwave radiation, the sun's energy reaches us as shortwave radiation.