It`s any day now. Then again, it also depends upon where you ordered it from. Amazon does well with general books but it`s kind of messed up when it comes to technicial ones as books like that tend to sit on shelves for a while and general book stores don`t like that because it wastes shelf space for books that do sell.
For example, Optical Shop Testing (a $150 book) had it`s first printing about 1978 and it`s second printing in 1992. That`s 14 years of sitting on the shelf for some of the books from the first issue. Please note that the second edition came out to correct the errors and add new material that became known after the first edition was published and not because the first printing was sold out. That`s a long time for a book to be "out of print" at a place like Amazon while there are plentiful copies available at the technical book stores.

If you want to get astronomy related books, the best place to go is to Willmann-Bell as they have specialized in the subject matter and have actually had several books published by a printer just for them.