A description of what happened in the sky pre-finale. The description-length is dictated by the word count sought by the publication you hope to appear in.
Since you just saw the display being described, you can relate to it.
Something before, during or after the events described set off a memory for the narrator, or the events themselves now turn into something else on a sentence.
An ambiguous sentence. Or a sentence that nails the events above to a cross. A sentence meant to be a revelation. A sentence that, were it the first one, would have made what you just read not worth reading.