Firmament

In reading Gen 1:1-2:3 the verses that caught my attention were about the second day 1:6-8. I think when I read it previously I thought it was referring to the earth's waters but I read it a number of times and this seems to be before God made dry land. So he is separating water below Heaven and water above Heaven. There is an interesting discussion on this here: http://www.kjvbible.org/firmament.html though I'm not sure it addresses how the waters are above the Heaven it does give a good interpretation of a lot of things.