Bereshit

1:5	God named the light 'Day,' and the darkness He named 'Night.' It was evening and it was morning, one day. Vayikra Elohim la-or yom velachoshech kara laylah vayehi-erev vayehi-voker yom echad.
1:6	God said, 'There shall be a sky in the middle of the water, and it shall divide between water and water.' Vayomer Elohim yehi rakia betoch hamayim vyhi mavdil beyn mayim lamayim.

Commentary:

sky
(Saadia) Rakia in Hebrew, literally 'spread' or 'expanse.' Usually translated as 'firmament.'