Frame of reference
Some spells and other effects, like time skip and wall of prodigal depth are not attached to any particular object, but stay still. The method for determining the frame of reference in which they are stationary is detailed below; unless it is hundreds of kilometers above the surface, it's going to use the planet's frame of reference.
A Referential Object is a collection of atoms that are contiguous with one another to a distance of no more than 8 nanometers (for the earth, this would include the atmosphere up to approximately 400 km), not including distances through entry points, such that no other Referential Object has it as a strict subset. The effect's frame of reference is that of the Referential Object with the greatest Referentiality relative to the effect, where Referentiality is calculated as (Referential Object's Mass / (Distance from center of Referential Object)^3)