I recently came across this: How do I know if my moon is full?

It's been closed as off topic by several high reputation users as not being about worldbuilding. It clearly is though, it's information someone needs in order to build a world.

We've discussed in the past and decided that just because something is on topic on another site does not make it off topic here. What is different in this case?

  • $\begingroup$ I feel like this has been asked and answered before...let me look around. $\endgroup$
    – James
    Commented Aug 17, 2016 at 13:53
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    $\begingroup$ I concur, this is on-topic to me. $\endgroup$ Commented Aug 17, 2016 at 14:12
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    $\begingroup$ I concur, and I'm probably one of the most avid and strict close voters on the site... $\endgroup$
    – Aify
    Commented Aug 18, 2016 at 7:47
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    $\begingroup$ We do need to sort this out. It appears we have a fundamental disagreement here. This question: worldbuilding.stackexchange.com/questions/52093/… is just another example. If we can't ask questions about the real world as is then we really don't have a whole hell of a lot to discuss. $\endgroup$
    – James
    Commented Aug 18, 2016 at 13:48
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    $\begingroup$ Related, not dup: meta.worldbuilding.stackexchange.com/q/3840/10851 $\endgroup$
    – cobaltduck
    Commented Aug 19, 2016 at 15:49
  • $\begingroup$ I was one of the close voters. James answer had swayd my opinion and I was about to vote for reopening, but just a couple minutes ago the question got migrated. Oh well... $\endgroup$ Commented Aug 26, 2016 at 3:44
  • $\begingroup$ @James nice you pointed that question - very important one for IRL, sad it is closed and I have missed it $\endgroup$
    – MolbOrg
    Commented Aug 27, 2016 at 21:37

5 Answers 5


Ok so this topic keeps coming up over and over again...and again.

The WB site description:

Worldbuilding Stack Exchange is a question and answer site for writers, artists and others using science, geography and culture to construct imaginary worlds and settings. It's built and run by you as part of the Stack Exchange network of Q&A sites. With your help, we're working together to build a library of detailed answers to every question about worldbuilding.

My best understanding of the consensus is this:

  • Questions regarding the real world are on-topic

We ask these questions to gain a better understanding of our world in order to develop and understand one that we are creating.

  • We have many questions about history, culture etc. and are essentially asking for a comparison or background information from reality for aid in developing our imaginary worlds. This is perfectly acceptable and has always been on topic.

It should be noted that the author chooses the site where they would like to post the question, this means they intentionally chose world building over another site and we should leave the question be.

In short: Getting a better understanding of how our world functions allows us to build other worlds.

If we don't allow questions about how a moon works, why should we allow questions about how certain building materials function, or why economies function the way they do, or why evolution selected for the freaking platypus?

Under the conditions set in @Michael Kjörling's post these would all have to be considered off topic. At least that is how I understand it...

Some relevant meta discussions:

Is the "international waters" question on-topic?

Should the help center be updated to specifically list real world history questions as off topic?

How do we feel about questions where the answer is "it exists in the real world?"

  • $\begingroup$ I agree with you, hopefully some of the people who voted to close can explain their reasoning though. $\endgroup$
    – Tim B
    Commented Aug 17, 2016 at 14:17
  • $\begingroup$ @TimB I do feel there is a tendency for this to happen more often with questions that are more heavily based on science. Which makes sense since there are sites specifically for such subjects...alliteration is fun. $\endgroup$
    – James
    Commented Aug 17, 2016 at 14:41
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    $\begingroup$ I agree with most of this, but I don't agree with rep-based decisions to vote to close. If it's off-topic here, vote to close regardless of the OP's rep -- and if it's on-topic here, we shouldn't vote close no matter who the OP is. Leaving a comment saying "you might also want to check out $site" is a good thing to do, but if the question fits here, we should keep it. The OP might ask a related question elsewhere; there's nothing wrong with that. $\endgroup$ Commented Aug 17, 2016 at 17:17
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    $\begingroup$ @MonicaCellio Indeed; a question is equally on topic or off topic regardless of who posts it. I would expect a question to be treated identically if I posted it under my regular account, or as an anonymous 1-rep user. Always focus on the content, not the person posting it. $\endgroup$
    – user
    Commented Aug 18, 2016 at 7:56
  • $\begingroup$ (And as a case in point, I didn't even notice that it was Tim B who posted this meta question until I was just about ready to click "post your answer"...) $\endgroup$
    – user
    Commented Aug 18, 2016 at 7:57
  • $\begingroup$ @MonicaCellio I see your point. I will edit that out. $\endgroup$
    – James
    Commented Aug 18, 2016 at 13:34
  • $\begingroup$ I just said this somewhere else, but personally I feel that if it is a "how does this work based on reality/science" It probably belongs on one of the other sites, where as "if I extrapolate into the unknown based on reality/science" it belongs here. $\endgroup$
    – Marky
    Commented Aug 19, 2016 at 14:29
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    $\begingroup$ @Marky That is inconsistent with what the site has allowed since it was created. Which is not to say you are wrong, that's what we are discussing after all. $\endgroup$
    – James
    Commented Aug 19, 2016 at 14:30
  • $\begingroup$ @James Yes, I know, so Im not expecting change or trying to make too much noise over it, but I still feel we field questions that would be more at home on other se sites $\endgroup$
    – Marky
    Commented Aug 19, 2016 at 14:32
  • $\begingroup$ @Marky it is not the question where Q fits the most WB or other place, but who fits where. $\endgroup$
    – MolbOrg
    Commented Aug 27, 2016 at 21:57

I was one of those who voted to close the question as off-topic, and also the one who initially voted to close it (thus pushing it into the close votes queue), so I figure I should explain my reasoning for doing so.

The information sought is certainly potentially useful in the efforts of building a fictional world, and you could certainly make a valid argument based on that line of reasoning that it should be on topic here because it has worldbuilding applications.

However, pretty much every single answerable question imaginable could pass that litmus test. I can conjure up a reason why almost any question that can be answered has applications in worldbuilding. Worldbuilding SE is not meant to be the kitchen sink, and in fact, as the site summary says (my emphasis):

Worldbuilding Stack Exchange is a question and answer site for writers, artists and others using science, geography and culture to construct imaginary worlds and settings.

This applies elsewhere on the network as well. For example, I could want to know how an AC-DC rectifier works, and ask about some detail of that on Super User, arguing that it should be on topic there because it's a part of how computer power supplies work, and Super User's scope is computers, thus it fits within their scope. But it's still not within their subject scope; such a question would be more likely to be on topic on Electrical Engineering or possibly (depending on its focus) Amateur Radio, which is also where people who are more likely to be able to answer it well focus their efforts. Just because something has applications to one field doesn't make it a part of that field, or pretty much every question on the network would reduce to being on-topic on either Physics or Mathematics:

Obligatory XKCD

Thus, I feel that by default for a question to be on topic on Worldbuilding there needs to be something imaginary about it, and generally speaking, the question should somehow be asking about that imaginary portion. A question can be off topic despite asking about something imaginary, and a question can include something imaginary that is completely unrelated to the question being asked, but a question that asks about something that is not imaginary is almost certainly off topic here.

There is nothing imaginary (note: imaginary, not imaginative!) about asking how to figure out how mundane celestial bodies interact in a normal solar system that could just as easily appear in real life. That's one of the things that the science field of astronomy is all about. Astronomy already has a subject-specific site, populated by experts in that particular field. An expert in astronomy is far more likely to be able to provide a good answer to how celestial bodies interact in general, than an expert in worldbuilding.

Asking how bodies in a specific, described solar system will interact would, if the solar system is constructed for the world being asked about, meet the bar of something imaginary because it postulates a situation that doesn't exist in the real world and asks how it would work out. But that's not what the OP in this particular case asked for help with.

Also note from our what topics can I ask about here? page:

For example, Worldbuilding SE welcomes questions on the following: /.../ as long as they are not about: (...among other things...)

  • Historical events of or historical facts about the real world, except when provided as examples or comparisons in the construction of an imaginary world (consider the History or respective subject-specific Stack Exchange sites)

While I feel that "historical" in that bullet point may be a somewhat unfortunate phrasing these days (it originated at a time when we were getting a number of questions about the history of our world, and reflects that background), I feel that bullet point is sufficiently generally applicable to be able to state that for the most part, questions about our own real world are off topic on Worldbuilding. Add something to it that is imaginary, and ask a question that focuses on the imaginary part, and it might very well become on-topic for us, as well as quite possibly becoming off-topic for the otherwise appropriate subject-specific site.

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    $\begingroup$ The imaginary portion is that we wouldn't calculate whether the moon was full or not in our world. We'd just walk outside and look. If we want to predict its future, we'd base it on past behavior. Because this is an imaginary moon, we can't do that. This is the kind of problem that worldbuilders would have and astronomers wouldn't. If anything, Astronomy should close it as speculative and send it here, not vice versa. $\endgroup$
    – Brythan
    Commented Aug 18, 2016 at 13:49
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    $\begingroup$ I agree with your litmus test comment, but I view it differently. Yes, in a way everything would then be on topic. But that makes sense to me since we are quite literally talking about creating a world. If we claim those are off topic how could we consider, building materials, economics, etc or anything else on topic? $\endgroup$
    – James
    Commented Aug 18, 2016 at 13:56
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    $\begingroup$ The discussion here seems very relevant: meta.worldbuilding.stackexchange.com/questions/567/… $\endgroup$
    – Tim B
    Commented Aug 18, 2016 at 15:42
  • $\begingroup$ Worldbuilding Stack Exchange is a question and answer site for writers, artists and others using science, geography and culture to construct imaginary worlds and settings. First is for whom it is, for specific peoples. $\endgroup$
    – MolbOrg
    Commented Aug 27, 2016 at 22:05
  • $\begingroup$ Ok, so practically anything could be on-topic? That's not a problem, unless you think it's more important to have categories to questions to close. I think that's a non-problem, and that the point (as I would wish it) is to welcome any questions relevant to world-building. This moon question seems like a great example of that. It's not a site about non-Earth-like world-building, hopefully, where anything too like Earth is off-topic. $\endgroup$
    – Dronz
    Commented Aug 30, 2016 at 21:09
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    $\begingroup$ If nothing is allowed to be off-topic, then admit it and update the topic description to say so. I completely agree with Michael, here. He's laid out a usable distinction to boot. I, personally, would like to see tools made to improve the ease of cross-referencing between questions (esp. between sites) and from questions to discussion pages and back, regardless, but it's particularly important on World Building. $\endgroup$
    – The Nate
    Commented Oct 1, 2016 at 23:09

Questions about the real world can be very valuable for builders of science-fiction worlds.

Most hard science fiction scenarios are an extrapolation of current developments into the future. In order to do this extrapolation we need to understand the current world. So a question like "Are humans still evolving in the old fashioned way?" is constructive because it gives science-fiction writers material for building a world centuries in the future.

  • $\begingroup$ Well put. I think if the question you mentioned were framed that way then no one would have voted to close it. $\endgroup$
    – James
    Commented Aug 18, 2016 at 14:12
  • $\begingroup$ I agree such questions can be valuable... but those questions should be asked in the SE forums for those questions. Once they have those answers, the authors can come back here and ask about the impact of those answers on imaginary worlds. $\endgroup$
    – SRM
    Commented Jan 30, 2017 at 5:42

This isn't a question about the real world, however the answer is based on the real world.

There are two factors here and they're getting confused. One is whether the question is on topic here, the other is whether this is the right place to ask the question.

While the asker is talking about his new planet and its moon, which is on topic here and we have people who could answer it. Worded slightly differently this question could be square in the middle of the field of expertise at astronomy SE and would be better asked there.


I think that the problem with this question is that it sounds like the poster thinks there is some standard equation for telling if a moon is full based on statistics like axial tilt. If people used such an equation to determine if our moon was full, then that might well be an on-topic question for Astronomy. As is though, I don't believe that that's how we figure out if the moon is full now or is going to be full in the future.

The way that I believe this works is that we determine if the (real) moon is full or is going to be full is that we make observations. Based on those observations, we've determined that the moon cycles between being full, gibbous, crescent, and new on a regular cycle.

The question though is about a fictional world. While its inhabitants may be able to observe its period, the author can't. The author has to use the available information to determine a consistent period.

If this were a real (in the sense of real world) astronomy question, we'd be going the other direction. Given when our moon appears full and other observable characteristics, what are statistics like period of revolution?

While the mistake is understandable, I believe that it is in fact a considerable mistake to regard this kind of question as off-topic. There's a high chance that astronomy will view it as speculative (not about the real world) and off-topic. If so, that leaves this question without a home, even though it is clearly about the setting behind a fictional world.

  • $\begingroup$ Vey well put, and you managed to get to the heart of what I was asking. $\endgroup$ Commented Aug 23, 2016 at 19:33

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