 | Olinthus Gilbert Gregory - 1802 - 590 páginas
...May 4, 1801 ? % It was observed in Art. 107 that, at a medium, the twilight begins in the morning, and ends in the evening, when the sun is 18° below the horizon : therefore if tt (in fig. 4, PI. II.) represent a parallel to the horizon drawn 18° below it, or,... | |
 | John Hubbard Wilkins - 1822 - 158 páginas
...This faint light before sun rise and after sun set, is called twilight. It commences in the morning and ends in the evening, when the sun is 18° below the horizon. But the sun's apparent daily course is more oblique to the horizon at some places than at others; and... | |
 | John Hubbard Wilkins - 1825 - 151 páginas
...This faint light before sun rise and after sun set, is called twilight. It commences in the morning and ends in the evening, when the sun is 18° below the horizon. But the sun's apparent daily course is more oblique to the horizon at some places than at others ;... | |
 | William Chauvenet - 1863 - 764 páginas
...for the moon. TIME OF THE BEGINNING AND ENDING OF TWILIGHT. 155. Twilight begins in the morning or ends in the evening when the sun is 18° below the horizon, and consequently the zenith distance is then £ = 90° + 18°, or h = — 18°, with which we can find... | |
 | William Chauvenet - 1864 - 726 páginas
...for the moon. TIME OF THE BEGINNING AND ENDING OF TWILIGHT. 155. Twilight begins in the morning or ends in the evening when the sun is 18° below the horizon, and consequently the zenith distance is then £ — 90° + 18°, or k = — 18°, with which we can... | |
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It commences in the morning and ends in the evening, when the sun is 18° below the horizon. 