The type of radiation from the sun with the longest wavelength is radio waves.

Here's why:

* Electromagnetic Spectrum: The sun emits radiation across the entire electromagnetic spectrum, from very short wavelengths like gamma rays to very long wavelengths like radio waves.

* Wavelength and Energy: Wavelength and energy are inversely related. Longer wavelengths have lower energy.

* Solar Radiation: While the sun is most known for its visible light, it also emits significant amounts of infrared radiation (heat), ultraviolet radiation, and radio waves. Radio waves have the longest wavelengths and lowest energy levels of all these types of radiation.

Let me know if you'd like to know more about the different types of solar radiation!