Zmanim

Zmanim (Hebrew: זְמַנִּים‎‎, literally "times", singular zman) are specific times of the day in Jewish law.

For either purpose, the status of the twilight hours just after sunset or just before sunrise is ambiguous. Judaism provides its own definitions for this period; at the same time, various rabbinic authorities differ on just how those definitions are to be applied for different purposes.

The Talmud often states calculations of these zmanim in terms of the time it takes to walk some distance, stated in "mils". Most authorities reckon the time it takes to walk one mil as being 18 minutes, though there are opinions of up to 24 minutes. Many authorities, indeed, hold such calculations to be absolute: if nightfall follows sundown by "the amount of time it takes to walk four mils," for example, that means "72 minutes after sundown" in all places on all dates. Other authorities, especially those living in higher latitudes, noted that the darkness of the sky 72 minutes after sundown (for example) can vary substantially from place to place, and from date to date. They therefore hold that "72 minutes after sundown" actually refers to how dark the sky is 72 minutes after sundown in Jerusalem on an equinox. Then that degree of darkness is reckoned as being true when the sun has fallen a certain number of degrees below the horizon (for example, 7°5′ below the horizon), and that becomes the actual standard used for all places and all dates.

One calendar day ends, and the next day begins, during the evening. The Talmud states there is an uncertainty as to whether the day ends at sunset or nightfall, so the time in between has a status of doubt. The Talmud in Pesachim states there are four mil between sunset and nightfall. However, the Talmud in Tractate Shabbat states that there are just three-quarters of a mil between sunset and nightfall.

According to the first opinion, nightfall is 13½-18 minutes after sundown (or its equivalent, sun falls 3-4° below the horizon). According to the second opinion, nightfall occurs exactly 72 minutes after sundown (or its equivalent, when the sun has fallen anywhere from 6.45 to 16.1 degrees below the horizon).

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