TSL

"We impute it, therefore, solely to the disease in his own eyes and heart, that the minister, lookinh upward to the zenith, beheld there the appearance of an immense letter,- the letter A,- marked out in lines of dull red light" (141).

This A is the size that Dimmesdale's sin has grown into. It's large and right before his eyes. This is what Roger is doing to him as he pulls the sin more and more out into the open so that Dimmesdale has not choice but to look tight at it. The meteor is the sin, I believe. It was described as, "so powerful... that it thoroughly illuminated the dense medium of cloud betwixt the sky and earth" (140). I am probably wring in this assumption, but I connect it to when Roger said, "a strange sympathy betwixt soul and body!" (125). Soul and the sky are the same: mystical and strange. Body and earth are the same: understood and scientific. The meteor and the illness Dimmesdale has are the same, something that is in between the two, or connects the two. They are both As, which represent the sin.