Even if AJ is right the Princesses still need to move the sun and moon.
 
We’ve got animals that don’t care for themselves, weather that only pegasi can change, and four seasons that require a big “clean up” every solstice.
 
Equestria is a messed up place.

Unstable orbit. Calestia and Luna just correct orbit every day.

And this is what happens when blind loyalty and lack of scientific questioning takes over a supposedly scientific purple unicorn.

@Militsiya
 
A.J.: Makes sense once ya think about it, too. Her special talent only involves the Sun, right? Well, once her sister was gone, she had to do something so we’d have night, too. Pro’lly started turnin’ the planet then, since it didn’t need quite as much magic, making that job much easier.

One visit to Canterlot later:
 
 
Twilight: So, all this time, she’s been rotating our planet, and not THE SUN! She never even told me about it!
 
A.J.: …Told ya so…

WE NEED FANFICTION OF THIS

@FanOfMostEverything  
And, when you realize that the ponies were still standing beside the mirror at the end of EQG?  

@Vocal  
Interesting. Especially if space travel gets involved.

@FanOfMostEverything  
My theory is that Equestria works in a near-temporal-stasis. The world itself experiences time as normal, and everyone goes about their business as usual, and to ponies looking out, without the use of magic, it would look like everything is at a standstill.  
And, to anyone looking in, it would look as though they were watching a world in ultra-fast-forward.

AJ’s model still works as long as magic allows for sustainable nuclear fusion at a lower mass. That, or the sun and moon are in unstable orbits and need frequent course correction.

Gah! Newton didn’t discover gravity, he just realized a new understanding of it!

@Prof.NightJack
 
e^(i*pi)+1 = 0.

Heliocentrism verses geocentrism.

Achievement Unlocked  
Fancy Mathematics

Later
 

hahaha nice!

*Isaac

I have my own headcanon concerning gravity and physics in Equestria.

Princess Celestia and Luna: Equestrias Longest Running Scam?

All i can think of is-