Observations of the solar ultraviolet irradiance during 1979 (solar maximum) by the Solar Backscatter Ultraviolet Experiment on the Nimbus 7 satellite have established that the irradiance at wavelengths between 200 and 300 nm is modulated by solar rotation. This short‐term variability, which is of the order of 3% at 200 nm and 1% at 250 nm, is associated with the evolution and rotation on the solar disc of plage areas which are enhanced in ultraviolet emission. By using ground‐based Ca II K observations of the fraction of the disc covered by plage during 1979, the intensity ratios for plage to quiet sun emission at these wavelengths have been derived. During the 11‐year solar cycle the number of plage regions on the solar disc increases. There is also an accumulation of active network arising from the remnants of decayed magnetic features. A three‐component model of the solar irradiance is used to estimate the temporal behavior of the ultraviolet emission between 200 and 300 nm, resulting from changes throughout the solar cycle in the active features on the disc. These calculations suggest that for solar cycle 21 the flux variability at 200 nm is 25%, decreasing to 10% at wavelengths between 210 and 250 nm, and to 2% at 300 nm. Ultraviolet flux variability of this magnitude corresponds to an average increase in the total solar irradiance from 1976 to 1979 of about 0.05%. For comparison, the average reduction in the total solar irradiance from 1976 to 1979 due to sunspot blocking is 0.07%. Because of the enhanced ultraviolet emission from solar active features, the variability of the total solar irradiance during cycle 21 is predicted to be less than is calculated by models which consider only the effects of sunspot blocking. This result is consistent with the need for an added faculae brightening term in total solar irradiance