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The Day and Night Terminator Across the Earth
How to compute the day/night terminator on a world map
Map (c)
Apple Computers, Inc.
More details:
Lines of simultaneous sunrise and sunset, lines of equal solar altitude
The elevation angle h of a celestial body at a given latitude is determined by it's declination and hour angle (tau)
sin h = sin(latitude)*sin(declination) + cos(latitude)*cos(declination)*cos(tau)
for rise and set: h=0
0 = sin(latitude)*sin(declination) + cos(latitude)*cos(declination)*cos(tau)
0 = tan(latitude)*tan(declination) + cos(tau)
The terminator can be calculated from:
tan(latitude) = - cos(tau)/tan(declination)
The coordinates (longitude,latitude) are
latitude
= arctan(- cos(longitude)/tan(declination)),
longitude = x+ tau, -180°<= x<= 180°
(c) 2006-2007 J. Giesen
Last update: 2007, Feb 02