| Concept definition: |
The <<TIME_OF_DAY>> of sunrise. The time of sunrise is defined to occur when the geometric zenith distance of the centre of the <SUN> is 90,8333 arc degrees; that is, the centre of the <SUN> is geometrically 50 arc minutes below a horizontal plane for an observer at MSL with a level, unobstructed eastern horizon under average atmospheric conditions. The upper limb of the <SUN> will then appear to be tangent to the eastern horizon. The 50 arc minute geometric depression of the centre of the <SUN> used for the computations is obtained by adding the mean apparent <<RADIUS>> of the <SUN> (16 arc minutes) to the mean amount of atmospheric refraction at the horizon (34 arc minutes). |
