Caption: An explication of the Venusian day.

Features:

1. Note: Venusian orbital period = 224.701 days, Venusian rotation period = 243.0226 days (retrograde), Venusian (synodic) day = 116.75 days (retrograde). The first two periods are relative to the observable universe and the third is relative to the Sun, of course, since it is the synodic day.
2. In the diagram, we are looking down on the Venusian orbit from north celestial pole (NCP).
3. Venus orbits prograde (counterclockwise) and axially rotates retrograde (clockwise). The axial retrograde motion may have been caused by a giant impactor in the early Solar System, but there are other theories (see Wikipedia: Venus: Orbit and rotation).
4. We put an imaginary giant mountain on Venus and start time at the Noon 1 position for the mountain on the diagram.
5. At 58.375 days (i.e., 1/2 Venusian day after Noon 1, Venus has orbited a bit more than 1/4 of its orbit and has axially rotated the mountain to the Midnight position for the mountain
6. At 116.750 days (i.e., 1 Venusian day) after Noon 1, Venus has orbited a bit more than 1/2 of its orbit and has axially rotated the mountain to Noon 2 position.
7. After one complete Venus orbital period = 224.701 days, Venus is back in at the Noon 1, but the mountain has NOT reached the Noon 3 position (which is NOT shown).
8. To reach the Noon 3 position, 2 Venusian days have to pass since Noon 1: i.e., 233.500 days since Noon 1 or 8.779 days after completing 1 Venus orbital period = 224.701 days.
9. Note the 2nd paragraph in the diagram is NOT clear and needs reworking---which it will never get.

10. We can calculate the synodic day of Venus from the synodic day formula given in file synodic_period_day.html. The Venusian orbit and axial rotation matches the assumptions of the synodic day formula well enough. We obtain

      P_day = P_orbital*P_axial/(P_orbital - P_axial) 
            = 224.701*(-243.0226)/[224.701-(-243.0226)]
            = -116.751 days,

    where the minus signs indicate retrograde motion. The calculated value agrees with the accepted value given above to within significant figures.

    Note a retrograde motion for the axial rotation relative to the Sun means that the Sun rises/sets in the west/east. This also clear from the diagram. Just imagination yourself on top of the mountain in the course of a Venusian day and recall that the direction to the west/east of the observer is clockwise/counterclockwise on the diagram.