If we keep moving down the cosmic ladder from Gods and Magic, I guess the next thing would be the planar system and the multiverse. However, I haven't really made many changes to those from what's written in the Dungeon Master's Guide. And with rumors flying about the next D&D setting being planescape-based, I plan on keeping it that way.
So instead, let's talk about the material plane, i.e. the universe the players will mainly interact with. And it wouldn't be very helpful to describe nebulas and galaxies, since Ahneria isn't a spacefaring planet yet. So we'll frame our discussion in terms that the game will actually be able to reference:
What do the skies of Ahneria look like?
Ahneria has one sun, which it circles once every 365 days. The rotation of the planet gives its inhabitants 24 hour days. I believe that unless your fantasy world is particularly affected by the odd length of day/night and year, you should make them generally analogous to the real world.
Of course, the sun is worshipped across the world as a blessing of Pelor, and indeed the sun and stars are products of his fight for light and warmth in the material plane. Within the doctrine of Pelor, day and night are designed to represent the struggle of light and dark, and the dangerous, monster-infested nighttime exists to make Ahnerieans more grateful for the light of day.
Pholtus, the trusted lieutenant of Pelor, is charged with keeping the sun moving through the sky. Folklore tells of his team of Ki-Rin which pulls the sun through the sky. Notably, even in old wives' tales, Pelor is somewhat distant from his worshippers - his blessings of the sun is all in service to his greater plan, to fight the darkness that envelops the universe. He is all-seeing and benevolent, but spreads his worship through his companion Gods.
Pholtus opposed this plan, but Rao, ever the voice of reason, suggested that this new sun could illuminate the night sky while the sun was away. The Gods of nature relented, realizing that without the sun to compete with, their new sun could shine even brighter. Thus was the moon born.
Of course, there is some truth to this story, but it likely happened long before the birth of mortals. The moon of Ahneria is called Luna in many cultures, derived from Ehlonna, one of the goddesses of nature. It cycles through its phases once every 13 and three-quarter days, meaning most calendars on Ahneria are divided into "months" of 14 days.
The phases of the moon include a full phase, which means that lycanthropes are a common problem in Ahneria. They lose control of their animal forms once every 13 or 14 days, making it hard for them to integrate into society. Stories of mysterious werewolves terrorizing towns are usually accompanied by strangers moving into the area or camping near the borders of civilized territory.
There are a few other celestial bodies that are visible from Ahneria in the night sky. These are the planets in Ahneria's solar system, and appropriately, they are usually named after the Solars of Pelor. Among the humans of Garlancia, they are called Secandi (the fastest planet), Anima (the brightest planet), and Viribus (the largest planet). They are often prayed to when people would ask Pelor for speed, magic, or strength.
These planets aren't actually the solars in question, and even if they were, they couldn't answer the prayers of mortals, being aspects of Pelor and not Gods themselves. It's just another way that people are faithful to Pelor, albeit indirectly.
The stars really are distant suns, though. A common aphorism is to point out that even in darkness, the light of Pelor can be seen still. The cynical reply usually has something to do with the fact that there is more night sky than stars, or that shadows are only cast by the sun.
In Garlancia, the stars and constellations represent Gods. Since Garlancia is close to the equator, the stars move parallel across the sky with little rotation, so they are vital for navigation and don't change much with the seasons. There is no "North Star", but there are plenty of large, bright stars that are named for important deities such as Rao, Pholtus, and others.
Speaking of the seasons, Ahneria has the usual four. In Garlancia, which is coastal and equatorial, the weather spends most of its time in a hot and balmy state, converting to a dreary and rainy sky for a several months a year.
Since there is much free-floating magic in Ahneria, odd weather is relatively common, with something odd happening about once or twice a year. This could be as benign as colorful rain or as harsh as boulders falling from the sky. Thankfully, the latter is rare in areas that have been populated.
As for the sky in the Feywild and the Shadowfell, I like the DMG description of eternal twilight and eternal night. So we'll go with that.
Using This Material in Your Setting
- What is the calendar like in your setting? If it's vastly different from the real-world calendar, why?
- What do people consider the sun to be in your setting? The moon? The stars?
- What are the phases of the moon? How do lycanthropes work in your setting?
- What other planets exist in your solar system? How are they named?
- What sort of constellations are in your setting? In the area you play in?
- How are the stars used? For prayer? For navigation?
- What's the weather like in your setting? If it's vastly different from the real world, why? How do the inhabitants deal with it?
- What are the seasons like in your world?
- Are there "shadow" planes of your world? What's the weather like there?