Given how magic is portrayed in the League of Legends universe, it stands to reason that magic there is a fundamental force of the universe that can be tapped in to. So let's talk about some stuff relating to that:
Firstly we have the Magical Friction, which Bard taps in to to traverse dimensions. All worlds emit the friction, but beyond that we don't know any other details. Given the limited insight here I've been inclined to believe that all magic is derived from this force that exists between realities where dimensions blur together and worlds literally collide. In that way the friction may act as a force that keeps the universe together by establishing boundaries and connections. I originally interpreted celestial magic as being the purest form of magic, and that other forms were essentially distilled versions of that power. I also liked to entertain the idea that the friction is why natural magic even occurs; the friction causes magic to radiate worlds and embed magic in to them naturally over time. Such reserves are finite but replenishable over the course of thousands or perhaps millions of years.
Then we have the Celestial Firmament, which is what Aurelion Sol is making; the stars. I interpret this as the magical friction, but a star version; a universal construct that keeps all the stars of the universe tied together and interconnected, with that celestial energy flowing between them in an endless cycle. It's not perfect, as all things have flaws and decay but it'll last for trillions of years at least.
Now I really don't know whether Celestial Energy is something people would constitute as magic, but given how Aurelion Sol's been a tad dismissive of magic as a concept, I'd imagine he either doesn't like that idea or that he finds the idea of "magic" amusing, in the way you find a dog trying to figure what the sod a reflection is amusing. I'm inclined to say that magic isn't the same thing as celestial energy, but I could be totally wrong here; my thoughts and theories have changed greatly over time.
Right now I'm picturing different universal constructs that work in unison to keep reality from going in to chaos, with the friction and firmament being part of this. Each has a force associated with it, in one magic, in another celestial energy, and while they are distinct they are powers that share origins and they do work in synchronicity, so celestial power and magic could intermingle in a way.
Then there's also spirits and the question of how those fit in, considering that we have Kindred, a being who is not a celestial entity, not bound by the laws of space and time, and not even physical most of the time, but totally a legit thing who doesn't fall in to either a magical or celestial category. Perhaps spiritual power is its own unique force and is crucial to the development of life and organisms, or is perhaps just fundamental to the universe as a whole, with the very idea of spirit encompassing all of reality and everything in it. I mean Nagakabouros is kind of a big deal after all. And then there's demons and how they fit in to all this. I don't feel like these things come under the category of magic, but instead that magic is just one key part of the whole show, as important a force as gravity, time or whatever.
That got rambly real quick so I'll sum this up:
- I think magic and celestial energy are distinct but intrinsically linked fundamental forces of the universe.
- These forces are governed by and originate from specific universal constructs such as the magical friction and the celestial firmament.
- Spiritual power comes in to play somewhere here, perhaps as a force of its own or an all encompassing force.
- Nagakabouros is a thing and should always be remembered because all encompassing serpentine Brahman deities have huge universal implications.
is tossing around) and 'nature magic' (hey there 
). IS there a difference apart from aesthetics? Or the intent of the practitioner? Why do some regions (Ionia) have more magic than others (Piltover)? Is there a natural philosophy behind the magic in Runeterra, or is this a 'it works just fine, thank you' sort of situation?
Ascendants, The 
Aspects, The 
Celestial Beings and 
Veigar.
weapons and armors use the magical power of the planet. 
Skarner is another example of an user of Magic from the earth itself or even 
The true Ice is also ice that is infused with the magic of Runeterra itself.
Void or the 
Glade) and the ones that come from the spirit of a being.
Shen, 
Spirits, 
Demons, 
Illaoi who uses the magic of her god... and magical creatures/races that are born with magic like the 
Dragons 
Yordles or 
Darkins.
who corrupts the True Ice, magic from Runeterra. 
or 
that corrupts and damages the spirits of themselves and others or 
uses the magic of the Cosmos and his own spirit since he IS a magical creature... or The Void Magic that aside from being "alien magic" corrupts the user and Runeterra. And the most common mix between the magic of the "Spirit" from the user and the Celestial Body (Runeterra).