薄明時の水平線の見え方について

概要

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This paper shows the results of an experimental study on the extent of the visible horizon, on the hue of fixed stars and planets in the duration of twilight in the South Pacific Ocean (36°-16. 2'S, 178°-09. 2'E). We thought the sight of the horizon depends upon the contrast between the luminance of the sky (L_1) and the luminance of the sea (L_2). That relation showing brightness contrast (C) is, C=(L_1-L_2)/L_1 (0≦C≦1) The results of this experiment are shown as follows; (1) The brightness of the sea surface depends upon the brightness of the sky. (2) The luminance of the sea surface which can be recognized in sight of the long telescope of a sextant is 0.05〜0.04cd/m^2 and then the altitude of the center of the sun is roughly-9 degrees. (3) Planets begin to become visible and unvisible just at sunset and sunrise. (4) The first magnitude fixed stars can be recognized in the sky when the altitude of the center of the sun is roughly-6 degrees. (5) The duration of nautical twilight is the period between civil sunset/sunrise and the altitude of the center of the sun, which is-9 degrees (the 1/2 of the duration of astronomical twilight).
社団法人日本航海学会の論文
1990-09-20