| Concept definition: |
The <<TIME_OF_DAY>> of moonset. The time is defined to occur when the geometric zenith distance of the centre of the <MOON> is 90,5666 arc degrees plus the apparent angular <<RADIUS>> of the <MOON> minus the apparent angular horizontal parallax of the <MOON>; that is, under normal atmospheric conditions at MSL, the upper limb of the <MOON> will then appear to be tangent with a level, unobstructed western horizon. No account is taken of the <<MOON_PHASE>>; that is, the <MOON> is always regarded as a disk in the sky and the upper limb might be dark. The 34 arc minute geometric depression of the centre of the <MOON> used for the computations is used to account for atmospheric refraction. The apparent angular <<RADIUS>> of the <MOON> varies from 15 to 17 arc minutes and its apparent angular horizontal parallax varies from 54 to 61 arc minutes. |
