Just to add some info, here are some commonly accepted definitions:
"A DAY" - "a period of twenty-four hours as a unit of time, reckoned from one midnight to the next, corresponding to a rotation of the earth on its axis."
"DAY TIME" - "the time of the day between sunrise and sunset; the time of light."
"NIGHT TIME" - "the time between evening and morning; the time of darkness."
As explained by Rabbi M. Lamm at an info website (aish.com), "The Jewish day does not begin and end at midnight as does the secular calendar day. Midnight is not a distinguishable astronomic event. In the era before the modern clock, a specific hour of the night could not be precisely known, whereas an hour of the day was easily determined by sighting the location of the sun. Thus, the day had to begin by precise, simple and universally recognized standards. This meant that the day had to be reckoned either from the beginning of night or the beginning of day.
In Jewish time, the day begins with the onset of night (the appearance of the stars) followed by the morning (which technically begins with the appearance of the North Star). According to some Jewish teachers, night and morning begin with sunset and sunrise respectively. For that is how the Torah describes it: "And there was evening and there was morning, the first day."
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