Magic Forums

I was reading a book about spellcasting, and it said it's best to plan certain spells to be cast based on the planetary hours and days, in addition to the moon phases and all the other timing and magickal correspondences. Have you noticed that there's a difference when casting certain spells at certain times?
I was also curious about what people think about the "dark" and "void-of-course" moons. Are those bad times to do spellwork?