As Bill Gottesman writes, it is very difficult also theoretically, to observe the passage of the Sun's rays from the inferior side to the superior one of an equatorial sundial.
The disk of the Sun in fact takes (in the the Spring Equinox 2002) 32h 30m to transit from one side to the other of the Celestial Equator. The Equinox occurs at 19h 15m UT What we can see depends also from the longitude of the place. For instance for a place with Long. 12 deg East , on March 20 th 2002: - the Sun rises with a small part (1.15 ') already above the Celestial Equator - at noon the part above is of 7.8 ' - at the sunset it is of 14.13 ' (less than half disk) Then during the whole day , the Sun illuminates both the superior and the inferior sides of the sundial On March 19, between the dawn and the sunset, the disk of the Sun is completely under, while on March 21 the Sun rises completely above the Celestial Equator For a place with Long. 100 West : - the Sun rises with 8.5 ' of the disk above the Celestial Equator - at the sunset the part above is 21.49 ' (more than half disk) For a place with Long. 180 West : - the Sun rises with 13.8 ' already above the celestial equator and sets with 26.8 ' of its disk that illuminates the upper side of the dial. Perhaps in September the things will go better :-) Best
