Translation:

12. Allah is He Who created seven Firmaments and of the earth a similar number. Through the midst of them (all) descends His Command: that ye may know that Allah has power over all things and that Allah comprehends all things in (His) Knowledge.

Notes (Tafseer)

5526. "Seven Firmaments." (Cf. ii. 29; xvii. 44; xxiii- 86; and xli. 12.)

5527. Literally: they are seven in number, each one separate from the other.

5528. But in all spheres of life and Creation, whatever conception we are able to form of them, it is certain that the Command or Law of Allah runs through them all, for His knowledge and power extend through all things.