ZmanCalculationMethod

An instance of this class represents a description for how a zman is calculated. The description may rely on other information provided in the ZmanDefinition (e.g. whether the calculation changes depending on the ComplexZmanimCalendar.isUseElevation setting).

Why are there so many ways to calculate a zman? The length of a shaah zmanis (halachic/solar hour) is calculated based on the length of the day. The definition of day has various opinions, and thus the length of a shaah zmanis varies. One such definition is dusk to dawn. Dawn can either be calculated as:

1. a fixed number of minutes before sunrise,

2. or as the moment that the sun reaches a number of degrees above the eastern geometric horizon - which happens before sunrise.

Sunrise is an astronomical phenomenon, not subject to varying opinions (save for whether to adjust for elevation). Dusk is often calculated as the inverse of dawn (i.e. after sunrise, and below the western geometric horizon), though some opinions place it orthogonally to their definiition of dawn (e.g. ZmanAuthority.AteretTorah in ComplexZmanimCalendar.shaahZmanisAteretTorah). The number of fixed minutes for sunrise/sunset is determined by the time it takes to walk the distance of a https://en.wikipedia.org/wiki/Biblical_mile. Some interpret those fixed minutes (let M = minutes) as measured by the position of the sun in degrees relative to the eastern geometric horizon M minutes before sunrise in Jerusalem around the equinox / equilux.

This is the distinction between the two aforementioned ways of calculating dawn. Some measure by the length of time it takes to walk 4 mil, while others measure using 5 mil. This is but one divergence of opinion in the calculation of shaah zmanis. Here are all of them:

1. Fixed minutes or degrees?

• Measure in fixed minutes or zmaniyos minutes?

2. How many minutes does it take to walk a mil?

3. Should a full mil be used to measure, or 3/4 of a mil?

4. Multiply by 4 or 5 mil?

5. Account for elevation or not?

6. When does day start/end?

• Dawn/dusk

• sunrise/sunset (which are astronomical phenomena)

• etc. see DayDefinition

Inheritors