Energy input to the Earth

We review the physical origin, spectral nature, energetics and known variability of all solar emanations: photons, particles and magnetic fields. Compared to a decade ago, our knowledge has greatly improved concerning variability in the total irradiance, as well as its EUV and UV components. It is noted that synoptic EUV-UV irradiance data from space will cease in 1990 owing to space-craft orbital failures and the present launch hiatus. The case for variability in the past few centuries and predictions for the near term are given.