[5] Another feature of this ancient practice is that, unlike the standard modern 12-hour clock that assigns 12 o'clock pm for noon time, in the ancient Jewish tradition noon time was always the sixth hour of the day, whereas the first hour began with the break of dawn according to many Halachic authorities,[6] and with sunrise according to others.
A division of day and night into twelve hours each was first recorded in Ancient Egypt.
A similar division of day and night was later made in the Mediterranean basin from about Classical Greek Antiquity into twelve temporal hours each (Ancient Greek: ὥραι καιρικαί, romanized: horai kairikai).
[23]The precise, intermediate time between day and night, or what is termed in Hebrew bayn ha-sh'meshot, has been discussed by Talmudic scholars in great detail.
The same time is described by Moses Alashkar as "from the moment that the entire circle of the sun sets [below the horizon] until there appear [in the sky] three medium-sized stars.
[26][27][28][29][30] Rabbeinu Tam, disputing, held the time of bayn ha-sh'meshot to be 58.5 minutes.
[32] In old times, the hour was detected by observation of the position of the sun,[33] or when the first three stars appeared in the night sky.
At the sixth hour, the sun is always at its zenith in the sky, meaning, it is either directly overhead, or parallel (depending on the hemisphere).
[35] Typically, nightfall ushers in more quickly in the low-lying valleys, than it does on a high mountaintop.
[71] Conversely, the Mishnah states that on the eve of Passover the daily whole-burnt offering was slaughtered at a half past the seventh hour, and offered up at a half past the eighth hour.