Smith's Bible Dictionary
Day. The variable length of the natural day, at different seasons, led, in the very earliest times, to the adoption of the civil day, (or one revolution of the sun), as a standard of time. The Hebrews reckoned the day from evening to evening, Leviticus 23:32, deriving it from Genesis 1:5 "the evening and the morning were the first day."
The Jews are supposed, like the modern Arabs, to have adopted from an early period, minute specifications of the parts of the natural day. Roughly, indeed, they were content to divide it into "morning, evening and noonday," Psalms 55:17, but when they wished for greater accuracy, they pointed to six unequal parts, each of which was again subdivided. These are held to have been -
1. "the dawn."
3. "Heat of the day," about 9 o'clock.
4. "The two noons," Genesis 43:16; Genesis 28:29.
5. "The cool (literally. wind) of the day," before sunset, Genesis 3:8 - so called by the Persians to this day.
Before the captivity, the Jews divided the night into three watches, Psalms 63:6; Psalms 90:4, namely,
the first watch, lasting till midnight, Lamentations 2:19,
the "middle watch," lasting till cockcrow, Judges 7:19, and
the "morning watch," lasting till sunrise. Exodus 14:24.
In the New Testament, we have allusions to four watches, a division borrowed from the Greeks and Romans. These were -
i. From twilight till 9 o'clock, Mark 11:11; John 20:19.
ii. Midnight, from 9 till 12 o'clock, Mark 13:35, 3 Maccabees 5:23.
iii. Till daybreak. John 18:28.
The word held to mean "hour" is first found in Daniel 3:6; Daniel 3:15; Daniel 5:5. Perhaps the Jews, like the Greeks, learned from the Babylonians, the division of the day into twelve parts. In our Lord's time, the division was common. John 11:9.
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Smith, William, Dr. Entry for 'Day'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/d/day.html. 1901.