Moonrise is defined as the instant when, in the eastern sky, under ideal meteorological conditions, with standard refraction of the Moon's rays, the upper edge of the Moon's disk is coincident with an ideal horizon. The transit of the Sun is local solar (sundial) noon. At high latitudes, neither of these statements may be true - for example, there may be several transits between rise and set. For observers in low to middle latitudes, transit is approximately midway between rise and set, and represents the time at which the body is highest in the sky on any given day. The transit time of a celestial body refers to the instant that its center crosses an imaginary line in the sky - the observer's meridian - running from north to south. At this time the illumination due to scattered light from the Sun is less than that from starlight and other natural light sources in the sky. Is defined as the instant in the evening, when the centre of the Sun is at a depression angle of eighteen degrees (18°) below an ideal horizon.
Is defined as the instant in the morning, when the centre of the Sun is at a depression angle of eighteen degrees (18°) below an ideal horizon. Astronomical twilight Beginning of morning astronomical twilight For navigation purposes at sea, the sea horizon is not normally visible. At this time in the absence of moonlight, artificial lighting or adverse atmospheric conditions, it is dark for normal practical purposes. Is defined as the instant in the evening, when the centre of the Sun is at a depression angle of twelve degrees (12°) below an ideal horizon. Is defined as the instant in the morning, when the centre of the Sun is at a depression angle of twelve degrees (12°) below an ideal horizon. Nautical twilight Beginning of morning nautical twilight The brightest stars and planets can be seen and for navigation purposes at sea, the sea horizon is clearly defined. At this time in the absence of moonlight, artificial lighting or adverse atmospheric conditions, the illumination is such that large objects may be seen but no detail is discernible. Ending of evening civil twilightĭefined as the instant in the evening, when the centre of the Sun is at a depression angle of six degrees (6°) below an ideal horizon.
Civil twilight Beginning of morning civil twilightĭefined as the instant in the morning, when the centre of the Sun is at a depression angle of six degrees (6°) below an ideal horizon. Sunset is defined as the instant in the evening under ideal meteorological conditions, with standard refraction of the Sun's rays, when the upper edge of the sun's disk is coincident with an ideal horizon. Sunrise is defined as the instant in the morning under ideal meteorological conditions, with standard refraction of the Sun's rays, when the upper edge of the sun's disk is coincident with an ideal horizon.
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