Thank you for your answer. I understand that the concept of night and day does not necessarily mean the presence of sun and moon, as you mentioned in your anwer. However, I’m still wondering what is meant by the first day in Genesis 1:5. Was it before the first evening started or after the first evening started? Thank you once more. Jaap Oosterhuis

ב"ה Shalom This is indeed a question raised by the commentators. There is a lot more than what meets the eye trying to understand the physical reality of creation while there is heaven and earth on the one hand, no luminary bodies on the other hand, and on this background light is created and there is evening and morning which constitute a day to be followed by other days. In my answer I will limit myself to the simple instruction of the verse. There are many commentaries, but I chose one which in my humble opinion makes the verse comprehensible without going into deeper levels of understanding which are not in the scope of this question and answer platform. The 19th century biblical commentator, (Meir Leibush ben Yehiel Michel Wisser (March 7, 1809 – September 18, 1879), known as the "Malbim" wrote, that the light was created and then straightaway it set, thus bringing about evening. Following 12 hours of dark, the light reappeared, hence bringing about morning which then constituted the first day. All the best