However, one quarter of a day a year was still
unaccounted for, so the calendar progressively moved
out of synchronization with the natural year by one day
every four years. The rising of Sirius (Sopdet) only
coincided with the calendrical New Year’s Day every
1,460 years -the event is actually recorded for 139cE.
Similarly, the thirty-day month did not coincide
with the natural cycle of the moon. Many festivals were
celebrated on the basis of observation of the cycles of the
moon rather than on the civil calendar.
The day itself was divided into twenty-four hours,
with twelve hours of day and twelve of night. The
passage of time was measured by water-clocks in the
form of a marked bowl from which water slowly dripped
through a hole.