The rather simple conventions used in the temperate zones for determining the times of sunrise (or sunset) and of the beginning (or end) of twilight at or near sea level are inadequate at heights, especially in the Arctic and Antarctic areas. They are not very satisfactory even at the surface in the tropics and in the polar regions. This report is intended to point out some of the difficulties and discrepancies and to suggest methods of improving upon the conventional approaches to the problems. It is hoped that it will serve as a basis of discussion- of the problems; involved and perhaps lead to some positive action being taken toward their solution. Some of the changes suggested here are based on the results of work on atmospheric refraction undertaken at Ladd Observatory of Brown University with the cooperation of the Office of Naval Research.
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