The Astral Sea is not a sea, of course. It’s more like a fantastic version of outer space. It’s filled with vast clouds of a luminous, silver-gray substance that is not mist and not liquid. Thousands of stars glitter in the distance, especially in darker portions of the plane. Vast expanses of “open air”  between these drifting clouds provide travelers with hundreds of miles of visibility, and even in the middle of the densest astral mists travelers can see objects several miles away with ease—the stuff of the Astral Sea just doesn’t impede vision much at all.  In fact, vision in the astral seems to vary based on size or "concept" of an object or area, and certain talents may allow creatures to "see" farther than others.

Someone floating in the astral doesn’t normally get wet or cold. A cool tingle on the skin is the only  sensation. Creatures who need to breathe can do so without trouble. The astral is survivable in most areas, but cold and deadly in "thinner" areas.  Winged creatures can fly through the astral stuff as if it were air, and natural swimmers can swim through it as if it were water. Other creatures can move slowly by desiring to move.

Even though the Astral Sea is a three-dimensional void, it possesses a distinct astral horizon that forms something like the surface of an ocean. The mists below this surface are darker and denser, and those above it are brighter and more open. Most creatures and objects slowly orient themselves toward this subtle demarcation without even realizing it, and travel toward their destination along the “surface” of the Astral Sea. Two vessels meeting in the Astral Sea do so on this unseen surface, so that encounters begin in a space that seems more two-dimensional than it is. Similarly, a vessel approaching a large or significant location normally does so from the area’s equivalent of sea level, or from its equator in the case of locations that are shaped like worlds.

Distances in the Astral Sea are unthinkably vast, but most travelers need only journey for a day or two before finding a color strand leading to their destination. However, finding a specific place in the Astral Sea itself (for example, a particular githyanki stronghold) may take much longer.

Features and Hazards

  • Like warp space, specific "non" locations may be analogous to locations in other realms such as the material.
  • Astral storms in astral, Bermuda Triangle like areas, winds/storms are the "color pools"?

Thought


If I were doing it, I'd treat transition between wildspace and the Astral sea the same as hyperspace works in Babylon 5. The common method is to do it at predetermined points ("jumpgates"), but being able to cross over under your own power is uncommon but not surprising. In B5, having on-board jump engines is usually a thing for capital ships, but in Spelljammer it would make more sense to be the result of actual spellcasting (perhaps a plane shift augmented by the helm).


In general, it takes from 10-100 days to travel from one Crystal Sphere to another. The sphere reached is random, unless you have either a guide or a device installed in the ship to show you the way. Shortcuts exist through spheres to other spheres. Some spheres drift into and out of proximity with each other, so that just because you reach an area once  does not mean that you will find it again.