What does the night sky look like on your gaming world? What, for that matter, does the daytime sky look like?

A few weeks ago, I was in a place where the night sky is truly amazing — at least when the clouds don’t impinge. The Milky Way is just right there, the Pleiades are big and beautiful, some of the globular clusters and galaxies are naked-eye objects, the entire sky is full of stars. It’s always wonderful to be reminded of what a beautiful universe we live in. And it reminds me of how interesting it can be to consider astronomy when you’re building worlds.

I suspect that in a lot of worlds, astronomy doesn’t really enter into it. Like biology or geology, we assume that a conworld has basically the same features as the Earth. There’s a Sun that goes around once a day, a single Moon that goes around once every 28 days or so, stars twinkling, etc.

And I suspect that there’s another category, just about as large, where the astronomy differs in a few standard ways: there are two moons, there are two suns, etc. With a lot of these, the astronomical differences still don’t mean much — they’re reminders that this isn’t Earth, but they don’t have much practical effect otherwise.

What ways are there of creating variant astronomy with interesting, unusual effects?

Well, before I get further into this, I should make it clear that I don’t think everyone needs to detail the astronomy of every conworld in some original way. Sometimes, standard tropes are standard for a reason: they work, they signal things in a simple way and they are evocative without requiring infinite work. And even if you want astronomy to come into it somewhere, it can be something the group devises after play has begun, perhaps left fallow for a useful, dramatic moment.

And I should also say that I’m going to stick to relatively plausible variations here. Could the night sky be full of rainbows and exploding candies? Well, yes, but if I start listing the more far-out variations, I’ll never stop.

Ideas for variations:

• The Sun: As I mentioned above, a standard trope is to have more than one Sun. What other variations are possible? Perhaps a planet might orbit a brown dwarf, leading to a very dim sun (and perhaps creatures adapted to seeing in infrared instead of what we consider visible light). Or orbit a vast giant, leading to horrible daytime temperatures. Or orbit with high eccentricity, leading to extreme seasons. Or have extreme axial tilt, also leading to seasonal extremes.
• The Moon: A lot of interesting variations are possible here. A world with no moons of appreciable size would have no tides. A world might have a net of tiny moons orbiting in complex ways. One of my favorite ideas is having a moon that itself has a biosphere. Calteir has a moon, called by some the Veil, which is mostly covered in clouds; only occasionally do complex blue, brown and green shapes appear behind the veil of white. (The moon itself is habitable, but I’ve never had a game become high-powered enough for the PCs to visit the Veil.)
• The night sky as a whole: Perhaps there are no stars at all in the night sky. Or there are only a handful of stars; or there are only stars in one section of the sky; or the night sky is so full of nearby stars that people talk of the Single Sun and the Many Suns (as might happen if the world orbits a star within a globular cluster).
• The Galaxy: Perhaps the world is embedded within an elliptical galaxy, leading to well-distributed stars in every direction with no noticeable ‘Milky Way’; or perhaps the world orbits a sun outside the main body of a galaxy, leading to a large galaxy viewable, as a whole, in the night sky; perhaps the world sits near-ish the central supermassive black hole of a galaxy, making for a great accretion disk and giant ejecta jets in the night sky.
• The Planets: Perhaps the planets all orbit closer to the Sun, meaning that they always appear as Morning Stars or Evening Stars; or perhaps they all orbit further out from the Sun, meaning they can be in any part of the ecliptic. Perhaps all the planets have such unusual orbital inclinations that the none fall near the ecliptic. Perhaps the world is itself a satellite of a much larger world, leading to interesting orbital mechanics and both a Sun and a Primary.
• The Pole: Our Earth has a star very close to the northern pole, and nothing in particular close to the south pole. (This situation has not always been so, of course.) Perhaps in your world, rather than a pole star, there is an open cluster or galaxy at the pole. Or nothing at all (as in the southern hemisphere of the Earth), making life harder for navigators.
• Other astronomical phenomena: Looking at the real night sky with our naked eyes, we can see a few open clusters (such as the aforementioned Pleiades), five planets, two or three galaxies (from the northern hemisphere, only M31 and our own), and one moon. And, if we have really good eyesight, perhaps a nebula or two, and maybe one or two more galaxies. But imagine what other interesting phenomena could be present in the night sky of a conworld: the tenuous layers of a planetary nebula, the strange spreading shapes of a diffuse nebula or supernova remnant, the dark majesty of a molecular cloud, or the speckled glory of a close-in globular cluster.
• Changing phenomena: In our night sky, the planets and moon move regularly. Meteors occur at semi-random intervals. Once in a lifetime, there may be a comet visible to the naked eye, and even more rarely, a supernova. At extremely rare moments, it might even be possible to see lunar impacts. But the stars, Milky Way and much more largely remains the same. What would it be like if this were not so? A planet near a globular cluster might see its stars move in obvious ways; a planet near a planetary nebula might see new layers slowly creep out. A planet with a ring and shepherd moons might see the ring wobble or twist on a daily basis. If our world orbited a star relatively near a black hole, we might see the night sky slowly (or maybe even quickly) lensing. Perhaps relativistic jets seeming to move towards us or away from us, too, as our star orbited.

Next time, a bit about some of the effects astronomy can be used for in gaming.