Antiquity Ancient Egypt In ancient Egypt the
flooding of the Nile was, and still is, an important annual event, crucial for agriculture. It was accompanied by the rise of
Sirius before the sunrise, and the appearance of 12 constellations across the night sky, to which the Egyptians assigned some significance. Influenced by this, the Egyptians divided the night into 12 equal intervals. These were
seasonal hours, shorter in the summer than in the winter. Subsequently, the day was divided into intervals as well, which eventually became more important than the nightly intervals. These subdivisions of a day spread to Greece, and later to Rome.
Ancient Greece The ancient Greeks kept time differently than is done today. Instead of dividing the time between one midnight and the next into 24 equal hours, they divided the time from sunrise to sunset into 12 "seasonal hours" (their actual duration depending on season), and the time from sunset to the next sunrise again in 12 "seasonal hours". Initially, only the day was divided into 12 seasonal hours and the night into three or four night watches. By the
Hellenistic period the night was also divided into 12 hours. The day-and-night () was probably first divided into 24 hours by
Hipparchus of Nicaea. The Greek astronomer
Andronicus of Cyrrhus oversaw the construction of a horologion called the
Tower of the Winds in Athens during the first century BCE. This structure tracked a 24-hour day using both sundials and mechanical hour indicators. The
canonical hours were inherited into
early Christianity from
Second Temple Judaism. By AD 60, the
Didache recommends disciples to pray the
Lord's Prayer three times a day; this practice found its way into the canonical hours as well. By the second and third centuries, such
Church Fathers as
Clement of Alexandria,
Origen, and
Tertullian wrote of the practice of Morning and Evening Prayer, and of the prayers at the third, sixth and ninth hours. In the early church, during the night before every feast, a
vigil was kept. The word "Vigils", at first applied to the Night Office, comes from a Latin source, namely the
Vigiliae or nocturnal watches or guards of the soldiers. The night from six o'clock in the evening to six o'clock in the morning was divided into four watches or vigils of three hours each, the first, the second, the third, and the fourth vigil. The
Horae were originally personifications of seasonal aspects of nature, not of the time of day. The list of 12
Horae representing the 12 hours of the day is recorded only in
Late Antiquity, by
Nonnus. The first and twelfth of the
Horae were added to the original set of ten: •
Auge (first light) •
Anatole (sunrise) •
Mousike (morning hour of music and study) •
Gymnastike (morning hour of exercise) •
Nymphe (morning hour of ablutions) •
Mesembria (noon) •
Sponde (libations poured after lunch) •
Elete (prayer) •
Akte (eating and pleasure) •
Hesperis (start of evening) •
Dysis (sunset) •
Arktos (night sky)
Middle Ages on the porch at
Bishopstone in
Sussex, with larger crosses marking the
canonical hours. Medieval astronomers such as
al-Biruni and
Sacrobosco, divided the hour into 60
minutes, each of 60
seconds; this derives from
Babylonian astronomy, where the corresponding terms denoted the time required for the Sun's apparent motion through the
ecliptic to describe one minute or second of arc, respectively. In present terms, the Babylonian degree of time was thus four minutes long, the "minute" of time was thus four seconds long and the "second" 1/15 of a second. In medieval Europe, the Roman hours continued to be marked on
sundials but the more important units of time were the
canonical hours of the
Orthodox and
Catholic Church. During daylight, these followed the pattern set by the three-hour bells of the
Roman markets, which were succeeded by the
bells of local churches. They rang
prime at about 6am,
terce at about 9am,
sext at noon,
nones at about 3pm, and
vespers at either 6pm or
sunset.
Matins and
lauds precede these irregularly in the morning hours;
compline follows them irregularly before sleep; and the
midnight office follows that.
Vatican II ordered their reformation for the Catholic Church in 1963, though they continue to be observed in the Orthodox churches. When mechanical
clocks began to be used to show hours of daylight or nighttime, their period needed to be changed every morning and evening (for example, by changing the length of their
pendula). The use of 24 hours for the entire day meant hours varied much less and the clocks needed to be adjusted only a few times a month.
Modernity The minor irregularities of the apparent solar day were smoothed by measuring time using the
mean solar day, using the Sun's movement along the
celestial equator rather than along the
ecliptic. The irregularities of this time system were so minor that most clocks reckoning such hours did not need adjustment. However, scientific measurements eventually became precise enough to note the effect of
tidal deceleration of the
Earth by the
Moon, which gradually lengthens the Earth's days. During the
French Revolution, a
general decimalisation of measures was enacted, including
decimal time between 1794 and 1800. Under its provisions, the French hour () was of the day and divided formally into 100 decimal minutes ('
) and informally into 10 tenths ('). Mandatory use for all public records began in 1794, but was suspended six months later by the same 1795 legislation that first established the metric system. In spite of this, a few localities continued to use decimal time for six years for civil status records, until 1800, after Napoleon's Coup of 18 Brumaire. The
metric system bases its measurements of time upon the
second, defined since 1952 in terms of the Earth's rotation in AD1900. Its hours are a secondary unit computed as precisely 3,600 seconds. However, an hour of
Coordinated Universal Time (UTC), used as the basis of most civil time, has lasted 3,601 seconds 27 times since 1972 in order to keep it within 0.9 seconds of
universal time, which is based on measurements of the
mean solar day at
0° longitude. The addition of these seconds accommodates the very gradual slowing of the
rotation of the
Earth. In modern life, the ubiquity of clocks and other timekeeping devices means that segmentation of days according to their hours is commonplace. Most forms of
employment, whether
wage or
salaried labour, involve compensation based upon measured or expected hours worked. The fight for an
eight-hour day was a part of
labour movements around the world. Informal
rush hours and
happy hours cover the times of day when commuting slows down due to congestion or alcoholic drinks being available at discounted prices. The
hour record for the greatest distance travelled by a cyclist within the span of an hour is one of
cycling's greatest honours. ==Counting hours==