Night-time observations from the orbiting astronomical Copernicus on May 14 and July 11, 1980, of visible light refraction by the limb of the atmosphere are presented. Irregularities of the measured refraction angle are then interpreted to be probably the result of the thermal fine structure in the stratosphere. The observations are very sensitive to horizontally stratified structures with temperature deviations of 2 to 5¿K, if the vertical dimension is less than 3 km. Since under selected geometric conditions the star's line of sight to the orbiting satellite sweeps out hundreds of kilometers at almost constant altitude, the observations are used to estimate the horizontal dimensions of thermal structures. Particularly large structures were found in the ozone region of the stratosphere. The refraction measurements are in general agreement with balloon soundings, UHF vertical soundings, and infrared radiometer observations of the limb.