And God called the firmament Heaven. So the evening and the morning were the second day.
Genesis 1:8
Surrounding context
1:7 Thus God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament; and it was so.
1:8 And God called the firmament Heaven. So the evening and the morning were the second day.
1:9 Then God said, "Let the waters under the heavens be gathered together into one place, and let the dry land appear"; and it was so.