When does the day begin? Well we all know that nowadays its begins at one second after midnight, but, that was not always so although we have some good precedents for saying it does start then.
But then, there are some good precedents for saying, "No. It starts in the evening," too. For instance when Jehovah God gave the Jewish nation instructions regarding observing the Sabbath he told them at Leviticus 21:28, 32 : "From evening to evening you should observe your sabbath." For God and the Jewish nation the day started at sundown and ran until the next sundown.
This was a pattern that God set himself. in the Bible account of creation Genesis 1:5 says about the first figurative creative day: "There came to be evening -- and there came to be morning, a first day." And the the other verses concerning the other creative days show that each of the other days also started in the evening.
The Jews had company in this practice of starting their days in the evening as well for the Phoenicians, Athenians, and Numidians also counted their days in this way.
On the other hand we too had some good precedents for starting our days sat the stroke of midnight. Both the Egyptians and the Romans began their days at this time -- as does most of the world today.
It has all come down to a matter of choice but it is easy to see why Jews today still count their sabbath day from sundown to sundown: this is a very logical ending to the day.
