Perihelion takes place in The Realm of Aethon, a very unusual solar system by our standards. Planets orbit a single star, and moons orbit most planets, but the similarities to our own solar system end there. All the planets are much smaller than Earth. The largest planet is only a fraction the size of our moon, and others are much smaller. The smallest satellites are only about 25 meters in diameter, meaning you could run around the entire planet is less than a minute.
The expanse between the planets is not a vacuum, it’s full of air. The entire solar system shares a single enormous atmosphere.
There are variations in gravity within the Realm.
All playable races are playable, and all monster races exist. Different races and species are native to different planets. Most playable races come from a planet where they are the dominant intelligent species.
- Dragonborn – Native to Varaha.
- Dwarf – Native to Regolith.
- Eladrin – Native to Crisium.
- Elf – Native to Sylvania.
- Half-Elf – Native to Charlon, a satellite that intermittently orbits both Sylvania and Gaia, the Elf and Human home worlds.
- Halfling – Native to Tarnar.
- Human – Native to Gaia.
- Tiefling – Native to Murugan
- Deva – Deva have no home world. They are reincarnated physical manifestations of ancient souls. They appear on nearly all inhabited planets, usually in sacred or wondrous locations.
- Gnome – Native to Kurma.
- Goliath – Native to Naruna
- Half-Orc – Native to Al Desh, a satellite of Gruumitar, the Orc home world.
- Shifter – Native to Lupaendore, the largest satellite of Gaia.
Years are counted from the Aethon Conference, when representatives of a dozens worlds met shortly after the dawn or airship travel. That was 162 years ago, meaning the current year is 162 AC. Years before that are counted reverse chronologically, as Before Aethon Conference, or BAC.
For the most part, technology is the standard D&D mix of medieval and magic. A notable exception are the magical airships used travel between planets. For more information, see Interplanetary Travel.