John Calvin Commentary Acts 10:11

"and he beholdeth the heaven opened, and a certain vessel descending, as it were a great sheet, let down by four corners upon the earth:" — Acts 10:11 (ASV)

The opening of heaven signifies, in my judgment, another thing here than in the seventh chapter. For it is said there that heaven was opened to Stephen, so that he beheld the glory of Christ; here Peter saw our heaven (the one we see) divided, so that a sheet came from there.