AbstractAircraft measurements of broad‐band infrared and solar irradiances together with radiance measurements at discrete angles and wavelengths are used, combined with microphysical observations, to investigate the optical properties of cirrus cloud.Results are found to be consistent with approximations appropriate to large particles with strong absorption in the thermal infrared. The observed angular scattering pattern is compared with other limited observational results and found to be consistent with them. Implications for predicting cloud albedo are discussed. An effective radius for the ice particles is also defined to enable solar absorption within the cloud to be predicted. Observations in the near‐infrared are shown to be consistent with this definition although the agreement is dependent on a number of assumpti