Question:
If you look at Genesis, you will see that G‑d created light on Day One. However, Scripture also says that G‑d created the sun, moon, stars, etc. on Day Four. So what was this light then that was created on Day One?
Answer:
The Talmud1 cites two views. One is that the light created on Day One was extremely brilliant, but G‑d foresaw that the world was undeserving of it, so He concealed this light for the righteous in the hereafter. According to the second opinion, however, the light created on Day One was in fact the light from the luminaries — which were then "hung in the sky" on Day Four.
Rabbi Eliezer Danzinger for Chabad.org
This point about the creation of light preceding the creation of the stars and planets is actually one of the strongest arguments for the truth of the bible. I've heard less-educated people claim this as a contradiction: "How could there have been light before stars ?". But we now know that at the the big bang, the universe was filled with intense light and radiation. It was only millions of years later that stars and planets formed. Of course you would still have to accept that a "day" and "waters" might be metaphorical ...