Amoment (momentum) is amedievalunit of time. The movement of a shadow on asundial covered 40 moments in asolar hour, a twelfth of the period betweensunrise andsunset. The length of a solar hour depended on the length of the day, which, in turn, varied with theseason.[1] Although the length of a moment in modernseconds was therefore not fixed, on average, a medieval moment corresponded to 90 seconds. A solar day can be divided into 24 hours of either equal or unequal lengths,[2][3] the former being called natural or equinoctial, and the latter artificial. The hour was divided into fourpuncta (quarter-hours), 10minuta, or 40momenta.[4]
The unit was used by medievalcomputists before the introduction of themechanical clock and thebase 60 system in the late 13th century. The unit would not have been used in everyday life. For medieval commoners, the main markers of the passage of time were thecall to prayer at various intervals throughout the day, and the passage of the sun.[5]
The earliest reference found to the moment is from the 8th century writings of theVenerable Bede,[6] who describes the system as 1 solar hour is equal to 4puncta, or 5 lunarpuncta,[7][8] or 10minuta, or 15partes, or 40momenta. Bede was referenced five centuries later by bothBartholomeus Anglicus in his early encyclopediaDe Proprietatibus Rerum (On the Properties of Things),[9] as well asRoger Bacon,[8] by which time the moment was further subdivided into 12ounces of 47atoms each, although no such divisions could ever have been used in observation with equipment in use at the time.
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