This seems to refer to the practice of Jews in fixing the beginning of the day, and consequently of the Sabbath, from the rising of the stars. They used to say, that when three stars of moderate magnitude appeared, it was night; when two, it was twilight; and when only one, that day had not yet departed. It thus came to pass (according to their night-day (νυχθήμερον) reckoning), that whosoever engaged in work on the evening of Friday, the beginning of the Sabbath, after three stars of moderate size were visible, was held to have sinned, and had to present a trespass-offering; and so on, according to the fanciful rule described.