Atmospheric Flattening of the Solar Disk

Abstract

IN view of the recently published measurements made at Princeton University of the oblateness of the solar disk, it is interesting to note that the apparent flattening caused by the terrestrial atmosphere is significant even at high elevations. A short computer programme was used to calculate the degree of flattening caused by a standard atmosphere above a flat Earth, assuming a solar diameter of 32 min arc. The results are given graphically in Fig. 1, in which the degree of flattening is measured in terms of the apparent major diameter. Table 1 relates these results to particular observing times at latitude +40°, showing that the effect can be considerably larger during the reported observation period than the actual measured oblateness of fifty parts in 10⁶. The effect could be substantially eliminated by forming the image of the disk in a vacuum behind a horizontal air–vacuum interface.