A book published by Harvard University Press in 1999, by JL Heibron, The Sun in the Church: Cathedrals as Solar Observatories, is quite interesting as Constantine, in the 4th century AD, was closely involved in a solar cult. The author says that since the Sun and the Moon are the most important objects in the sky and influence the rhythms of our existence, did the Church determine the position and motion of the Sun? To measure the meridian a hole in the south facing wall of an ediface would allow a beam of sunlight to fall on a line directed N to S on the floor of the ediface. Since a large dark enclosure was required to observe the changing position of the sunbeam on the line churches were obvious places to install such meridiana. Churchmen encouraged this as it had a practical side effect – it helped determine the calendar of Christian feast days, particularly Easter. According to tradition it fell on the first Sunday after the first full Moon after the Vernal equinox. Heilbron goes on to tell how this was done in various churches, mainly in the Papal States. The Sun is in effect, the Grand Illuminator and upon its entry through the meriadiana hole it illuminated the Church – but is there a longer tradition for a role of the Sun in Christianity?