The ESV translation uses the terms "Heaven" and "the heavens" in verses 8 and 9 of Genesis 1 in a way I find confusing:
8And God called the expanse Heaven. And there was evening and there was morning, the second day.
9And God said, “Let the waters under the heavens be gathered together into one place, and let the dry land appear.” And it was so. ESV
Does the Hebrew indicate a plural in verse 9 and singular in verse 8, or is it more consistent with the singular used in both cases by the NET translation ("sky" and "the sky" respectively).