Definitions of Astronomical events
Sunrise/Sunset is defined as the instant in the morning/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.
Beginning/Ending of civil twilight is defined as the instant in the morning/evening, when the center of the sun is at a depression angle of six degrees (6°) below an ideal horizon. 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. The brightest stars and planets can be seen and for navigation purposes at sea, the sea horizon is clearly defined.
The brightest stars and planets can be seen and for navigation purposes at sea, the sea horizon is clearly defined.
Beginning/Ending of nautical twilight is defined as the instant in the morning/evening, when the center of the sun is at a depression angle of twelve degrees (12°) below an ideal horizon. At this time in the absence of moonlight, artificial lighting or adverse atmospheric conditions, it is dark for normal practical purposes. For navigation purposes at sea, the sea horizon is not normally visible.
Beginning/Ending of astronomical twilight is defined as the instant in the morning/evening, when the center of the sun is at a depression angle of eighteen degrees (18°) below an ideal horizon. 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.
I think that works out to be sunset + 48 mins (averaged). But his wil depend on time of year etc.etc. easiest way is to use the tables provided in the
aip