In my last post, I explored some ways in which you can make the astronomical properties of a conworld unusual and interesting. Astronomy can have interesting, evocative, creative effects on play, too. Here are some impacts it can have:

• Shaping the way people live: I know of at least two conworlds where the night sky is completely devoid of stars. This could lead to a sense of hopelessness, or one of rugged individualism. And how does it affect psychologies when the sun is always in the sky (as in summer in high latitudes) or never in the sky (winter in high latitudes)? What if the sun were always present? What if “day” and “night” were caused by pulsations of the sun, rather than rotation of the planet? What if the moon were visibly creeping closer to us — would that lead to foreboding, or joyous exultation? It’s easy to imagine any of these variations causing a hundred rippling effects through the lives of people in those worlds, from psychology to agriculture.
• Shaping navigation: This aspect of daily life has especially strong astronomical connections. In the real world, the sky can give you a very specific sense of latitude, if you know how to read it. And if you have a good clock, you can tell your longitude as well. What would it be like in a world with nothing at all in the night sky? Perhaps travelers would avoid nighttime travel altogether, lest they become lost. What if the stars moved visibly on a day-to-day basis? Navigation might be a vastly more convoluted, and esoteric, skill.
• Informing the sense of place: In addition to helping or hindering how you get to a place, it can help shape your sense of that once you’re there. Different areas within a world are likely to have different approaches to the sky, often reflecting variant cultural mores. If the moon(s) resemble those of Earth, then months are likely to map closely to the orbital cycles of moons, regardless of place; that’s the derivation of the word “month”, after all. But different places may have different calendars, leading to discrepancies in what date someone thinks it is, or even what year. A culture’s constellations are likely to betray some of their cultural values. If the “Flaming Dragon” is rising in the East, that may be reason to stay only in stone houses for a month or two… And in our world, different latitudes see different stars, meaning it’s very hard to see the Magellanic Clouds if you’ve never been outside the northern hemisphere. Being able to see stars, nebulae, planets, even moons that you’ve never been able to see elsewhere can make a foreign place seem all the more foreign. But seeing the same moon can remind you of home. Describing the night sky can greatly help the sense of immersion, and the sense of the world as a distinct place.
• Affecting character generation: The positions of the stars could have direct mechanical effects on a character’s innate abilities. The primary example of this I can think of is HârnMaster, where a character’s skills are directly affected by the star-sign they’re born under. And of course Blade & Crown allows characters to be Fated, which could be derived from astronomical influences. Can you think of other games where astronomy or astrology comes into character generation?
• Affecting abilities during play: Many games give astronomy an indirect effect on play, often through the form of giving bonuses to certain rituals when performed on appropriate holy days. This came up in a recent thread on RPG.net about games where the calendar has a mechanical effect during the game. But I can imagine a game where even more astrological effects come into play: presence of given constellations in the sky, planets within certain constellations, eclipses, etc. This would be especially easy in a system with free tagging, such as FATE.
• Soothsaying and fortune-telling: ‘Disaster’ originally meant “bad stars”, and it’s easy to conceive of various astrological effects on a character’s fortunes. As I mention in Blade & Crown, this is a great way to use changes of Traits in play, as they are inspired by astronomical phenomena.
• Creating tension through timing: Confluences of astronomical phenomena may allow, or disallow, certain events. Perhaps the Portal into the Mountain-Queen’s Realm is only open on the equinoxes; or the only way to fulfill the prophecy is to “let a thousand stars fall” by waiting for a meteor shower; or the magical staff only draws power from the light of the Four Moons shining together; or the curse can only be broken on a day without night. These can all lend tension of timing to a situation. Of course, like any time-restricted events, they can lead to the PCs waiting around for the right confluence, or missing the confluence entirely.
• High-powered adventure locales: If your characters are getting too big for their britches, a voyage to the moon might be fun!

What other uses have you found for interesting astronomy in your games? SF settings almost don’t count, with their unusual astronomical phenomena so frequently found all over the place, but I’m curious about whatever setting you’ve thought of!