> (1) Astronomical twilight begins (altitude = -18 deg) > (2) Nautical twilight begins (altitude = -12 deg) > (3) Civil twilight begins (altitude = -6 deg) > (4) Sunrise (altitude = 0 deg) > (5) Sunset (altitude = 0 deg) > (6) Civil twilight ends (altitude = -6 deg) > (7) Nautical twilight ends (altitude = -12 deg) > (8) Astronomical twilight ends (altitude = -18 deg)
Looks evident. But I remember that (4) and (5) corresponds to an solar altitude of -(0 deg 16 '). This is due to the refraction (-34 ') and the radius of the suns disk. - Daniel Roth
