bain
This method returns the beginning of bain hashmashos (twilight) according to the Yereim (Rabbi Eliezer of Metz) calculated as 18 minutes or 3/4 of a 24-minute Mil before sunset. According to the Yereim, bain hashmashos starts 3/4 of a Mil before sunset and tzais or nightfall starts at sunset.
Return
the Date of 18 minutes before sunset. If the calculation can't be computed such as in the Arctic Circle where there is at least one day a year where the sun does not rise, and one where it does not set, a null will be returned. See detailed explanation on top of the AstronomicalCalendar documentation.