In Chapter 12, it is a meteor which comes to symbolize both Dimmesdale's guilt and Governor Winthrop's goodness. The meteor is described as
"a light (which) gleamed far and wide over all the muffled sky. It was doubtless caused by one of those meteors...burning out to waste, in the vacant regions of the atmosphere".
Looking up at the phenomenon, Dimmesdale beholds a sign of his sin,
"the appearance of an immense letter, - the letter A, - marked out in lines of dull red light".
After preaching the most powerful sermon of his life the next day, the tormented minister speaks with the old sexton of the church, who sees the meteor as evidence of the holiness of Governor Winthrop, who died that night. He says,
"...the protent that was seen last night...a great red letter in the sky, - the letter A, which we interpret to stand for Angel. For, as our good Governor Winthrop was made an angel this past night, it was doubtless held fit that there should be some notice thereof!"