Or considering the population of the earth, it could be millions born in the special hour. So it stands to reason that it is a lot more complicated than it appears to conceive and give birth to a star born. Lash hinted that it was to Harry, she made it clear that it took a lot of planning on Margaret's part for it to happen. It is also clear that in her choice of Malcolm to be her star child's father Margaret was trying to break the mold for the norm of what a star child is.
Presumably it only affects those born "in the that light" i.e. the spot light (which I am sure would occur during the night/early morning). So I would presume it's quite literally a cosmic light, hitting one side of the planet. That would include all of North America (USA, Canada), Central America, Cuba and the Central American islands, Mexico, the most nothern parts of South America (i.e. parts of Brazil etc), parts of the Artic Circle, the western part of Russia, parts of Japan, parts of China, parts of Korea, parts of New Zealand and Australia (and a number of Pacific Islands), and some parts of South-East Asia.
My guess is though it isn't all of them surely, for the number would be higher. It will be a literal thing like "born under a blood moon" type of thing. Will it matter if the births are indoors? Not sure. Will the babies need to be sanctified? Not sure. Will those who are in the light who are not babies be affected? Unclear.
So many questions.
It strikes me that Listens, another Starborn knows Chicago well enough to be a forward planner for the Fomor. Another Chicago native? Was he responsible for the books and belts in SF and FM? Did he plan the way for Cowl in GP? Was he a Red Court agent until there was no Red Court and the go to the Fomor? And was he a Black Council agent all along?
You are thinking the entire Earth, but what if it’s like a solar eclipse?, there is a path? where it plays over only part of the earth for an hour the witching hour), and Chicago was the only big city in the path this time (Romania last time for Drakul’s current body). If that can be plotted then it can be predicted, you merely need to time the birth for that specific hour in that pathway. Easy using time dilation of the Ways.
Remember everything boils down to Chicago, Changes is the only book where something significant in the Supernatural world happens outside of Chicago.
I think you might be right about Listen. He is just has too much on the ball.
I also agree that Chicago is clearly the centre of everything for some reason, and your theory about how it might be just a particular area might make sense. Perhaps the light is only focussed on a particular place, and Chicago would make sense.
Not enough data. There is nothing in the text that indicates where Harry was born. The closest we get to that moment is placing Margaret and Malcolm at the Lincoln Monument just before Harry is born. Given the 666 year cycle it could be some type of comet or asteroid. There is no way to know. Butcher could be basing it on something like Highlander, there can be only one! I know one thing. He has a fascination with vampires.
That is true. As I said earlier though, I would say on balance of probabilities it's likely in America, and Chicago seems to be the most significant place in America in the series. No idea why that is (in terms of in-universe reasons, obviously we know the Doylist reasons that Jim needed to set the series there). There are enough references to Highlander that I am sure that it has something to do with everything...that being said there isn't much real-world myth to back up Highlander and from what I have seen of Highlander and researched about the greater universe it is in, there isn't a lot that links to the series. In fact, it's so general it could link to anything. However, there is a thing about the source of immortality in Highlander being linked to a cosmic conjunction where literally every planet in the universe somehow "lines" up.
He does have a fascination with vampires, and there significance in the series is more than just monster-of-the-week. I'd say there is a link to the greater secrets of the series yet I can't tell what it is.