Zodiac and Mystaran moons
by LoZompatore.Here is a kind of a "poster" about the known astronomical data for the Mystaran solar system.
Most of the information are included inside the picture itself, so I add just a few more comments:
I took the zodiac's constellations from the Starmap of CM7 module. Even if this starmap suggests different dispositions of the constellations in the Mystaran sky (i.e. they could not be zodiacal constellations but polar constellations instead) I noticed that there are exactly 12 of them, and that they are somewhat referred to Mystara's seasons.
So I considered them as the equatorial constellations related to the astrological signs.
Other canon material (mostly the PWAs) gives a different name to the zodiac constellations (except for the Hydra), so I thought that the CM7 assigns to them an elvish name, while the PWAs show the human name of the same groups of stars. Stars/galaxies names come from the CM7 so they should be considered "elvish" names.
I added some astronomical data that may be easily calculated for Mystara and its two moons (once that the orbital periods are known it is possible to calculate the distance from the sun or from Mystara).
Data about Matera and Patera's gravity are available in CoM Designer's Manual, so it is possible to compare their mass to some real solar system equivalent.
Once the distance from Mystara of the moons is known, it is possible to make a comparison between the apparent size of the real moon in the Earth sky and the apparent size of Matera and Patera in the Mystaran sky. Notice that if Patera would be visible, it will appear as a huge celestial body.
Other information I put in the picture include some data for the diskworld, an artificial habitat created by Terra on the fringes of Mystaran solar system and described in the CoM Designer's Manual. I also added some speculations about the Dragon constellation and the legend of the Darokinian dragon Aurus described in IM2 module.
I tried also to determine the phases of Patera along the Mystaran year. It was not an easy task, but I hope I included the major astronomical contributions. Basically, this moon rotates on a polar orbit in 3 days and a half; this polar orbit is also locked to Mystara (again, from CoM), which means that Patera shows always the same side to Mystara's surface. Patera also precedes around Mystaran axis so to complete a full circle in a Mystaran year. These two movements let the external sun light to lit every month a different region of Patera's surface.
That's about all. I didn't include information about the other planets (the ones described in the Immortal set) because they should be very similar to the real world solar system data (except for Damocles, of course).