There are a lot of plots that introduce a special event that occurs every 1000 years, some of them involve a celestial conjunction. Eclipse, lunar or solar, is the most common used. During this event, magic power is greatly enhanced (might be only certain magic school, or general magic).
What is special (magically) on a conjunction?
It is understandable that past people regard solar eclipse as a bad omen because of the darkness and the disappearance of the sun, but what gives the mages extra oomph when this (and other conjunction) happens?
This takes place in our solar system, so the same sun, moon, earth, other celestial bodies. You can make up hidden characteristics of the bodies, like they emit a stream of mana or magical power, or such.
- Spell activates by manipulating mana: invisible energy that fills the atmosphere, not necessarily uniformly. You don't need internal mana to cast spells, instead manipulating those already in environment.
- To use magic, you only need to know the principle that govern the spell and "will" it, so it is a common thing, except complex spells are harder to understood so it will not be available to most people.
- The power increase is greater the more massive the celestial bodies involved.
- Anyone can learn magic as long as they are capable of understanding the working of the spell. This makes wizards/mages as common as scientists, and twice as cool and and weird.
- The increased effect varies with location and time.
Additional backgrounds (optional)
You can use this, or part of this, as hints, or not.
- Lunar phases affect water magic. Interestingly enough, lunar eclipse increase water magic, instead decrease it. The same applies to solar eclipse.
- You can cast spell as long as your brain can handle it. If your brain is tired, your spell may fail and may even cause unexpected result (some may be developed into new spells)
- You can cast multiple spells at once, though those capable of this feat are very, very rare.
- Magic integrates into daily life, and most people know how to use it in simple form.