Astronavigation

Astronavigation is the art of using Astrum based magic to travel between the Worlds, i.e. travelling through "space" (often referred to, in various native languages, by a phrase that translates to "the deep-sky", as space in the Astrum Skies setting is not a vacuum, see below) to different planets. It is usually performed by Astrologers, who may specialize, among other things, in crafting flying vessels or in the piloting of the same, although some perform both.

The Deep Sky, the Space between the Worlds

"The Deep Sky" refers to the space between planets, where the air is thinner and gravity is far weaker. This interplanetary atmosphere allows for travel aboard ships enchanted with special magic that allows them to catch solar winds in their sails, and eventually reach incredible speeds in the thin air. Travel from one world to some of its moons may take a few days, or travel between planets in one solar system might take a few weeks. Longer voyages between stars might last months, or up to a few years to travel from one side of the galaxy to the other. As stars are a source of Astrum, the sails can catch a charge that is expended when ships slow down to approach their target destination.
The air in the Deep Sky often smells dusty, but Astrosailors often describe it as a 'cool, clean dust' that can be quite refreshing, and can often get very poetic about that very specific, memorable aroma. The scent does indeed come from stardust, but in most of space is not thick enough to cause issue, although sailors that spend decades in the void tell tales of lung diseases associated with prolonged exposure to the dust. In certain regions of space it coagulates into clouds and eventually nebula, which contain their own unique climate and weather patterns very distinctive from those on planets. Nebula Storms result in fantastic lightning displays. Solar winds can become more turbulent in nebula, causing spinning vortexes or even eddies that can trap starfaring vessels in vortexes thousands of miles wide.
Temperatures can vary greatly in the Deep Sky and is proportional to the strength of solar wind. As one approaches a star, it can exceed desert like temperatures, and further away can feel like tundra. Almost all of space is what one might call "habitable", in that well prepared travellers who dress for the occasion or space-born creatures adapted to the harsher conditions can be found nearly anywhere aside from areas extremely close to stars or in certain regions of space, known as "windless" zones. These are areas where the solar winds stagnate and temperatures drop too low for almost anything to survive. A ship that falls into such a dead zone has little hope of escape before the crew freezes to death without some other sort of propulsion system on board.
As solar winds travel away from stars, and since larger stars typically have stronger winds, astrologers must be very specific about their courses for interstellar travel. If travelling a straight line between two equally sized stars for example, one would reach a midpoint half way through where the current of the star behind them gives way to the one in front of them, and the vessel will transition from sailing downwind to upwind. In this situation, like a seafaring vessel travelling upwind, a series of zig zag maneuvers can be performed to travel up solar winds directly toward a star, although it increases the distance, and thus the time, traveled. It is not uncommon for the second half of such a trip to last twice as long as the first.
Additionally, since larger stars typically give off more solar winds, more often than not the quickest route between two stars is not a straight line, but rather one would navigate along "windy routes" following a trail of multiple very large stars and catching the stronger winds. A layman might mock the twisty, curvy routes of an experienced astrologer, and be shocked to learn that a winding course multiple items the distance of a more obvious route actually takes a fraction of the time. This leads to the establishment of well known routes where trade and travel can be accelerated and where many ships congregate. The largest of these routes might even be granted protection from piracy by guilds or governments stationing larger defense vessels there. The sharing of known space routes is a common sign of diplomatic good will between allied countries, and many a astrologer or astrosailor has made a lifelong career as a scout, seeking out better and newer routes good for travel and various needs.

Starships, Sailing the Solar Winds

Flying vessels enchanted with star magic designed to sail the Deep Sky go by far too many names in far too many languages to condense to any sort of list, but many of them have several, necessary features in common. All are powered by Astrum, and are effectively flying vessels. Often they are normal ocean borne sailing ships that have been fitted with special sails that can catch solar wind as efficiently as atmospheric wind, although the thick air in the skies directly above planets make flight just as slow as sailing on the surface of water. This dependency on solar winds makes "lift-off" virtually impossible at night, and is far easier when the sun is lower in the sky at just before dusk or just after dawn, so that the solar winds are parallel to sea level. This allows the ship to gain the momentum required to lift itself into the sky and away from the planet. The smallest of skiffs may be able to obtain flight around high noon, but the feat is impossible for larger vessels.
The purposes of solar ships are as varied as those of seafaring ships. They most often transport trade goods and passengers between the Worlds. They can also be used for governmental purposes such as diplomatic envoys or military craft. Additionally, interstellar piracy is of course one of the more concerning dangers of travelling the Deep Sky. Any vessel rigged with the specially enchanted sails described above can be used for space flight. Most often, normal ocean faring vessels are used as they can also land in the water of their destination planets, avoiding great potential for damage to the hull when landing on celestial bodies with large amounts of gravity, and allowing for easy seafaring travel planetside. Additionally however, some larger ships are never intended to make landfall. Perhaps they carry smaller transport ships to make landfall, or are designed to only dock at 'space ports' built on asteroids or small moons with minimal gravity, or they are large flagships in great military armadas.
The magic that enchants the sails of a starship also, usually, includes gravity magic as well, allowing for a sense of normalcy in that regard aboard the decks of the ship. This magic replicates gravity on and very near the ship, typically to point down toward the ship's bottom, although the magic quickly dissipates a few meters from the hull. The strength of the gravity field is chosen when the sails are crafted, but typically is just a bit weaker than that of an average planet, allowing for 'springy steps and longy jumps' as an astrosailor might say. This varies depending on the maker however. Sometimes ships are built to have no extra gravity; allowing for the quite whimsical freedom of weightlessness aboard the craft; such a ship would be built with a covered upper deck to prevent sailors from floating off. On a gravity rigged ship, a man overboard will quickly fall out of the gravity field and begin floating freely in space.
The crew of a starship almost always has a captain, an astrologer, perhaps a quartermaster, and any necessary deckhands. This setup perfectly matches the outfit of a seafaring ship, but replaces any navigator position with that of the astrologer. The astrologer's main duty is in fact to plan the course for a ship before they set sail, charting out routes of strong solar winds, but also includes maintaining the 'skyworthiness' of the sails, ensuring they are functioning properly, casting any repairation spells upon them as necessary, and while the helm is sometimes manned by the captain or quartermaster, often the astrologer pilots the ship as well. Any quartermaster worth their salt will always consult with the astrologer to get good estimates on the trip's duration in the best and worst case scenarios to ensure adequate food and supplies are stocked for the crew.