My journey to revising my world began one evening at work while idly browsing Wikipedia on nearby star systems (I had gotten there from a slashdot article on an exoplanet).

Now quick aside, there's a seen in the movie Krull where you have the setting of the two suns that I always thought was cool and awesome and from teenage years I had had my world be in orbit of a binary star pair. Naturally twice the sun meant twice the orbit for the same solar energy, so the calendar was expanded out to this weird setup where humans counted in half years of 360 days since there was 8 seasons in any orbit (two suns in sky, summer, one winter right).

Wild, fantastical to be sure, but that day I started reading up on what the truth of a planet in a binary star system would be like and, honestly, the science truth is even more amazing and fantastical than the fantasy I had concocted. So I co-opted it.

The lesson I took from this that I'll be applying to my mapping is realistic accuracy, even in a fantasy setting, can add more to the depth and feel of that setting than it will ever detract. The more real the "real" things of a setting are, the more fantastic the fantastic things can be, IMO.

And eventually some stellar cartography will be in order for my setting. As it stands here's the cosmos of the setting as we would understand it - that's important to note since the people of the world still firmly believe it is flat and the stars of the universe orbit their world...

Carthasana is the third planet of the larger of two stars in a binary star system. The star it orbits is the same size as our sun. Carthasana's orbit is slightly more perturbed than ours and takes 365.7629 days to complete - this means the calendar has skip years rather than leap years: every fourth year a day is skipped to keep the solar calendar in sync. Carthasana has one true moon and two asteroids it has managed to capture in orbit around it. The nearest asteroid appears as a very bright star in the morning or evening sky of -5 magnitude. It's orbital period is 10 hours. The asteroid out has a 4 day orbital period and a maximum magnitude of -4. Carthasana's moon is the same size as ours (for reference a full moon has magntiude of -12.6).

The other star in the binary pair is called the cold sun since it lies too far away to provide any appreciable warmth (It does provide the fraction necessary to offset the effect of Carthasana's slightly further orbit from its sun though). Seasons do not pass with respect to it. This said it is still a -20 magnitude object (the sun being -26.73 by comparison) - or about 100,000 times as bright as a full moon. This means the presence of the star in the "night" sky turns it from black to a deep blue color and blotting out stars in the sky with magntitudes less than 3 (about the same effect as light pollution in modern urban environment).

It takes 80 years for the stars to complete a revolution around their shared center of gravity. This means that sunrise and sunset times for the cold sun change slowly over that 80 year cycle on Carthasana - if the two suns rise together on Midwinter it will be 80 years before they do so again.

Half the year is lit well enough that armies can move. This will affect the history of the world. Throwing fantasy considerations back into mix I've ruled that at least some kinds of undead are linked to the light of the cold sun.

Part of my setting revision will be writing software that can track these movements and let the DM know how much light is available at any given time in the year - since the night and day isn't a clear indicator as not all "nights" are dark, and nights when neither cold sun nor moon is in the sky are rare indeed.