There are many contradicting models of the 'Verse and creator Joss Whedon has not published anything official. The closest thing to official is the "Complete and Official Map of the Verse" by QMX. But it is riddled with astronomical impossibilities. The companion piece, "The Verse in Numbers" is, in my opinion, even worse. The authors come up with some outlandish ideas to explain why all the planets have Earth-like gravity, days and seasons, etc.

I take a different approach. We only visit less than a dozen worlds in the entire series and movie. Maybe those worlds just happen to be Earthlike in gravity. And of those worlds, only a handful are visited long enough to get some idea of how long their day and night are. None of them are visited long enough to have any idea at all how long their seasons or local year are. Gravity between 80% and 120% of Earth's and days between 20 and 28 hours long might not be significant enough to neccesarily depict in a TV show.

So I have my own version of the map of the 'Verse, based on the map by QMX and taking some info from TViN, but a little more astronomically possible. I won't say it's not highly unlikely, but it's a little more possible. The map does contradict the show and movie frequently, but when it comes to travel times, I think the script places a location for plot convenience. So my map does contradict the show here and there. But, it's internally consistent, which is important for a campaign.

Using the World Generation Rules for Classic Traveller and GURPS Traveller, I created the summary charts on the pages below. The Traveller Universal World Profile lets me look at a world's entry and have an idea of the world, the Universal World Trade Number and Trade Classifications let me look at two worlds and calculate how much commerce passes between them.

I just read The Verse in Numbers 2 and I see that they have addressed some of my issues, among them the positioning of habitable planets too close or too far from a star. Again, they have come up with some ideas which might work in a super science fiction setting, but which I feel are excessive for the Serenity setting.

White Sun
Red Sun
Blue Sun