Why when the sun is blocked out on Angel in season 4 it isn't blocked out in Buffy season 7?
Within the continuity of the show, the blotted-out sun was localized to LA. This is why all of the vampires began traveling to Los Angeles -- if the sun were blocked out everywhere, the vampires would have just stayed where they are.From a real-world perspective, Buffy and Angelaired on different networks for Buffy's 6th and 7th season (Angel's 3rd and 4th, respectively). They was initially a moratorium on cross-over appearances that kept Buffy cast members from appearing on Angel, or vice-versa, until S04E15, "Orpheus", where Willow arrives to restore Angel's soul. This meant that major cross-over plot lines would have been very difficult to execute between the two shows.