The profound psychological effect made on man by the regular change from day to night is a theme in the aggadah, epitomized in Adam's fear upon watching the first sunset (Av. Zar. 8a). In the Scriptures and in the aggadah, night has negative associations. It is a time of fear and danger, a symbol of death and of the return to chaos (cf. Ps. 91:5–6; Song 3:8). Day has positive connotations. The converse view, however, is also expressed. The day comprehends dangers of its own ("the destruction that wasteth at noonday," Ps. 91:6), whereas night is a time for rest and the renewal of strength. God appears to man at night (Gen. 15:12; Job 4:13); it is "an acceptable time" for prayers also and most appropriate for meditation (Ps. 77:7; cf. "The night was created only for study," Er. 65a).
In contrast to pagan mythology, where sunrise represents a daily contention between opposing forces, in Jewish monotheism, the day-and-night cycle is attributed to a single God who "forms the light, and creates darkness" (Isa. 45:7), "who changes the times," and "who removes the light from before the darkness and the darkness from before the light" (beginning of the evening prayer). The special religious significance attached to this periodicity can be observed in the Temple rites of regular morning and evening sacrifices and in the benedictions over the daily cycle in the morning and evening prayers (the benediction "Creator of the luminaries" in the morning prayer, and the benediction "Who brings the nights" in the evening prayer). Every morning, when darkness disappears before the light, the initial act of creation is renewed. In biblical cosmogony, the concept that at first there was "darkness on the face of the abyss" compares with a similar view on the origin of the universe of other early cultures. In contrast to Greek mythology, however, it is not the darkness, or the abyss, that "gave birth" to the light. The day was created by the order: "Let there be light." The halakhic postulate "the day goes after the night" is based on this antecedence of darkness to light and of night to day (Gen. 1:5). The 24-hour cycle starts at sunset; Sabbath and festivals begin in the evening, and terminate at the start of the following night (a number of specific day-only fasts, however, start at dawn; see
). Certain concepts, dating probably from the pre-biblical period, reflect the belief that day is the basis of all that is good; these concepts have entered the Bible (e.g., Ps. 104:2; Dan. 2:22; Isa. 30:26) and the Apocrypha, and more especially gnostic and other writings with a dualistic tendency. Traces of the dualist theory are found in Jewish folklore and it may be assumed that the belief that Jewish redemption will come in an era when
there is perpetual day derives from it. The concept was accepted, at least poetically and symbolically, both in the Bible (Zech. 14:7) and in the aggadah (Ḥag. 12a).
During the talmudic and subsequent periods, many superstitious beliefs relating to night took root in Jewish folklore.
, known in Assyrian and Babylonian mythologies as a flying demon (e.g., in the Epic of Gilgamesh), was the most feared of the evil night spirits and a fiend especially dangerous to women in confinement. Although there is no relation between her name and the Hebrew word laylah ("night") the phonetic similarity converted her into a night-demon threatening the lives of newborn babies, especially uncircumcised males; she is also a succubus that clings to men sleeping alone (Shab. 151b). To stave her and other diabolic creatures off, the rabbis forbade people to go out alone at night, especially on Wednesdays and Fridays (Pes. 112b). Charms, amulets, adjurations, and potions, as means of protection against "the terror by night" (Ps. 91:5), were widespread in many Jewish communities until quite recently.
The halakhah attaches great importance to the day-and-night cycle. Many mitzvot may only be performed during the day, e.g., circumcision, the sounding of the
, putting on the tefillin (phylacteries), lulav ("the taking of the palm-branch"), the laying of the hands on, and the slaughtering of, sacrifices, genuflective prayer, testimony and judgment, the construction of the Temple, and others.
The Bible does not clearly define day and night or their divisions, such as "evening, morning, and noonday" (Ps. 55:18), the watches of the night (Ex. 14:24; Judg. 7:19), midnight or half the night (Ex. 11:4; 12:29), and the notion of "hour" is not mentioned at all. The duration of a "halakhic" day is from dawn until the appearance of the stars, i.e., a full solar day; it is divided into secondary periods, according to three systems:
(a) Every day (and every night) is divided into 12 "variable" ("זמניות") hours, no matter what season it occurs in; the duration of the hour is therefore dependent on the yearly season (Sanh. 38b). Ultra-Orthodox Jews in Israel follow this system to the present day.
(b) The entire day (day and night) is taken as one unit and is divided into 24 standard and fixed hours of 60 minutes each, as in the commonly accepted time system. The division of day and night into fixed hours, with a specific duration, is mentioned for the first time in the literature of the tannaim (see, e.g., Mekh. SbY to 12:29: "He is seated on the sundial [a time device probably introduced into Ereẓ Israel during the Hellenistic period] and shows the hours with an accuracy that is within a hair's breadth"). The notion of an "hour" as an undefined and not standardized lapse of time has, however, been maintained in the Mishnah ("The early pietists waited an hour.…"; Ber. 5:1). Though it was only theoretical, there was also more detailed division; an onah ("term") is 1/24 of an hour, an et ("period") is 1/24 of an onah, and a rega ("moment") is 1/24 of an et (Tosef., Ber. 1:3). In this classification the rega is approximately ¼ of a second. The rabbis, therefore, said that "a human being … does not know his ittim [plural of et], rega'im [plural of rega], and hours … but God … entered into it by a hair's breadth" (Gen. R. 10:9). A different, more precise calculation existed in Ereẓ Israel: "How much is a rega – 1/58,888 of an hour" (Ber. 7a). A wide literature, notably the Baraita de-Shemuel, deals with such time calculations within the framework of astrological research. Another division of the hour is into 1,080 parts; this is also very ancient and is based on the lunar month.
(c) The solar day (alone) is divided according to the changes in the brightness of the sunlight. In this system, the day is divided as follows: dawn, the appearance of the first morning twilight, is the starting point when all precepts to be fulfilled during the day become obligatory. Halakhah, however, prefers sunrise to dawn because the commencement of the day presents problems of definition; haneḥ ha-ḥammah ("first appearance of the sun") occurs after dawn and precedes zeriḥah by the period of time it takes to walk a mil ("mile"). At that time, the pious read the Shema. Zeriḥah – full sunrise – is the moment when the entire sun appears over the horizon. Sunset is the moment when the entire sun disappears below the horizon. Evening twilight is the light after sunset and it is doubtful whether this period may be called day or night, and diverse opinions have been given by the tannaim as to its exact nature and time (Shab. 34b). According to Maimonides (Yad, Shabbat 5:4), the evening twilight begins with sunset and lasts until the appearance of three medium-sized stars, and from then on it is night. R. Tam argues that evening twilight begins from the period it takes to walk three and a quarter mil after sunset to the appearance of the stars. Until then, it is still day. In the Shulḥan Arukh (OḤ 261), this second opinion is accepted as binding. According to a third opinion, held by some of the early commentators, night begins immediately with sunset and the evening twilight is a period prior to sunset, lasting the time it takes to walk three and a quarter mil.
The halakhah used systems (a) and (b), while (c), which is the most ancient and is based on the direct observation of the movement of the celestial bodies, is only of secondary importance. All the hours and time concepts associated with the precepts are "variable." According to
's Levush and
*Elijah ben Solomon
of Vilna, the hours of the day are calculated from zeriḥah to sheki'ah (sunset); the majority of opinions, however, maintain that the calculation is from dawn until the appearance of the stars. The Shulḥan Arukh decides in favor of the second opinion. In the same way as the day, the night is divided into "variable" hours (there are three watches in three parts of the night), but this division is devoid of any practical importance, except for "the middle of the night," which is the time for reading Tikkun Ḥaẓot (the midnight prayer). "To keep a man away from sin," the rabbis limited to midnight the time for performing a number of precepts which otherwise could have been fulfilled during the whole night (Ber. 1:1).
The "standard" hours (according to system b) are used in halakhah to set related periods of time, such as "six hours"
between the eating of meat and milk, "one hour" for the salting of meat, and many others.