A Crude but Effective Open Scheme

The most basic epicycle-deferent system had each celestial body moving uniformly along its own epicycle, while the center of that epicycle moved uniformly along a deferent centered on Earth.

It explained why some celestial bodies did not move as regularly as the Sun rising in the east and setting in the west: what orbited Earth was not the celestial body itself, but the center of its subordinate orbit, and sometimes the body even appeared to move backward.

Of course, at this stage, both the epicycles and deferents were perfect circles. They did fit geometric aesthetics, but their accuracy was not especially high. The epicycle-deferent system truly capable of accurately calculating the movements of numerous celestial bodies would have to be Ptolemy's version.

More precisely, it should now have been called an epicycle-deferent-eccentric system.

As a reference frame based on Earth, this system complicated a simple problem because of its perspective. Yet sometimes, that reference perspective was more important than the complexity of the calculations.

"But this system can't simply be applied directly..."

The system was based on Earth, and Earth did not move. While Manus was on Earth, he could use this system directly. But if he took that shortcut, then once he entered outer space and was far away from Earth... this magic would become useless.

Moreover, he needed to add other supplementary positioning measures to help him establish a celestial positioning model on other levels.

At present, this system only contained knowledge from Muggle astronomy and mathematics, making it somewhat too narrow for the magical field.

If Manus entered the Mental World, this system would likewise fail instantly. That would not do.

"I can develop a Locating Spell to assist in building this system, perhaps incorporating the astronomical knowledge of the wizards in this world... or even astronomical