Here, Astromancy used to receive Magical Energy from Space before being relegated to just reading the future and Holmes states that the original form of Astromancy draws Magical Energy from the Earth's Rotation, the Magical Energy that fills the sky and the magical energy that rains from the Heavens.
Here, Holmes and Da Vinci further clarify Ancient Greece has 3 different layers separating them(Earth, Sky, Heavens) and Wodime is using the Heaven's Layer(Which govern the laws of Outer Space) to "manipulate the Planets to become a gigantic Magical Circuit" to create a rain of Meteors.