A
moment (
momentum) was a
medieval unit of time. The movement of a shadow on a
sundial covered 40 moments in a
solar hour. An hour in this case means one twelfth of the period between
sunrise and
sunset. The length of a
solar hour depended on the length of the day, which in turn varied with the
season, so the length of a moment in modern
seconds was not fixed, but on average, a moment corresponds to 90 seconds: A day was divided into 24 hours (of unequal lengths, twelve hours of the day and the night each), and an hour was divided into four
puncta (quarter-hours), ten
minuta and 40
momenta.