I'm wondering if there are any regular, realm-wide events (about every century or so) that would affect the Material Plane. Either nearly everybody knows it's happening, or just that strong magic-users would feel it.
I love the Great Modron March, but it's too long between events. Maybe a comet or celestial alignment? Something along those lines, though, would be nice.
Answers focusing on 5e lore are preferred, but I'm open to existing lore as well.
Thank you, in advance, for your time and knowledge.