on physic · 11:51am Apr 22nd, 2014
you know what always bugs me is when people talk about eclipses happening in equestria. it's a geocentric system with the sun and moon diametrically opposed, right? they cannot eclipse - aside from that one time when they shared the sky due to screwy everfree magic kidnapping the princesses. so by extension, the sun and moon are likely the same size and orbit at the same altitude.
from where does the need for celestia and luna arise, then? i would posit they are needed to give the sun and moon boosts of force to let them continue / stabilize them in their orbits. this coincides with dawn and dusk over equestria, although it means that in other far-off places, the sun might tend to jerk forward a bit at noon, for example.
but when one mass orbits another in a 3+1-dimensional system, it needs no extra force to keep it going, yeah? we see that nowadays with our moon and with any number of geostationary satellites. (low earth orbit satellites need thrusters so the atmosphere doesn't drag them down.) so here, i posit that either one of the two following things may be true.
1: something about gravity is screwed up, say that inertial forces tend to outweigh (heh) the force of gravity for some inexplicable arcane reason.
2: there is some vacuum medium that causes drag and slows the sun and moon down. perhaps a magic background field, a pervasive thaumic medium of some sort? there's another word but it escapes me. essentially a luminiferous ether.
is there a finite speed of magic? i would think so, even just based on shown evidence, and it's nowhere close to light speed.
There's a problem with that. If the sun and moon were always diametrically opposed, then the moon would always be full. Crescents are a big part of Luna's iconography.
2034516 Eh, I call it tradition. It wasn't always a geocentric system.
In any case, my ultimate point that I was trying to get to before my phone battery died, was this:
Due to relativity, a geocentric system where the Sun and Moon orbit the Earth is indistinguishable from a system where the Sun and Moon are still and the Earth rotates. The "jerk" of acceleration at sunrise would go the opposite way if you're in the Earth's frame of reference. I was just annoyed by people who say "Celestia is not really raising the sun, it's all a scam, she's just making the Earth rotate." The two scenarios are effectively identical, which makes the idea of a conspiracy pointless. What would be more focusable for a conspiracy is that in any set-up, the Sun and Moon would need additional force to keep moving at all. But I think that could be explained by some manner of ethereal magic gradient (THAT's the word!) that causes drag on matter.
2034911
So the sisters have to keep things moving because of the luminiferous aether?
Eh, makes as much sense as any other model of Equestria's cosmology.