The domification method “Placido” is based on diurnal motion, that is the apparent motion of the celestial sphere in 24 hours, observed from a specific place on the Earth, and on temporal hours.
TEMPORAL HOURS
The temporal hour is obtained by dividing the daytime arc of the sun (from rising to sunset) and the night arc (from sunset to the next sunrise) into twelve parts.
The solar temporal hour will be 60 minutes only during the two days of the Spring and Autumn equinoxes. In these two days the Sun travels, in its diurnal motion, the full Celestial Equator. For this reason the 60 minute hour is called equinoctial hour.