# Moons coinciding with months possible?



## OGone (Mar 2, 2012)

Basically I'm quite a pedantic person and even though on my fantasy planet they are short of the technology required able to view the solar system I still want the solar system model to be there and working.

Basically...
-There are eleven Gods in my World.
-One God is represented by the Sun and one God by the moon (the moon is just like our own).
-There are 365 days a year, 9 months a year lasting 40 days each and 5 "excess" days used celebratory.
-Just like our planet there's also a quadrennial excess day too.
-The final nine Gods are to be represented by moons or planets up in the sky, coinciding with the seasons.

All other variables are interchangeable. My World has no seasons and can be any size due to the fact that the land I am building is in fact a comparably small group of islands on the planet and the rest of the sea is not traversable and left undiscovered so the world could potentially be any size and the group of islands can be positioned anywhere on the world for my idea to be feasible.

How could I make this work, mathematically, so that each month a different planetary body is visible in the sky? I've been thinking either an inner ring of planets that the World passes due to orbiting at a higher speed or a ring of moons surround my World on an elliptical orbit. Anybody confirm that these would be feasible or suggest another way in which this could make sense?

Thanks!


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## Steerpike (Mar 2, 2012)

I think either idea would work, though with the ellipitcal ring of moons you'd have to figure tidal effects (are there going to be any tides?)

Also, maybe your planet could have a weird orbit, like perpendicular to the plane of all the other planets in the solar system.


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## Devor (Mar 2, 2012)

I'm having trouble lining things up mentally in a way that would work, if I'm understanding you correctly.  Unless the other planets actually circle the earth, I don't see a regular pattern forming of one revealing itself each month.

My advice is to cheat.  All of the planets are close enough to be visible all the time (or at least, certain times of day), but some sort of magic obscures all but one a month.

((edit))  There actually were some planetary theories where the planets circled the earth, and the earth circled the sun, pulling them along with it like the moon. So I guess maybe you could do that.


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## OGone (Mar 2, 2012)

Steerpike said:


> I think either idea would work, though with the ellipitcal ring of moons you'd have to figure tidal effects (are there going to be any tides?)
> 
> Also, maybe your planet could have a weird orbit, like perpendicular to the plane of all the other planets in the solar system.



You're right actually; the tidal effects would be too tough to figure out. I think I will have to go with the planet idea.



Devor said:


> I'm having trouble lining things up mentally in a way that would work, if I'm understanding you correctly.  Unless the other planets actually circle the earth, I don't see a regular pattern forming of one revealing itself each month.
> 
> My advice is to cheat.  All of the planets are close enough to be visible all the time (or at least, certain times of day), but some sort of magic obscures all but one a month.
> 
> ((edit))  There actually were some planetary theories where the planets circled the earth, and the earth circled the sun, pulling them along with it like the moon. So I guess maybe you could do that.



I am not sure if my idea makes sense either to be honest. However, imagine my world is Earth in this image: http://www.aerospaceweb.org/question/astronomy/solar-system/solar-system.jpg

What I am trying to say is we can see Venus from Earth with a pair of binoculars (it appears as a star otherwise). Imagine nine planets, perfectly spread out and lined up while moving in unison along the same orbit as Venus. Imagine they are moving slower than Earth so that Earth can bypass them and line up perfectly with each one every 40 days... Does that make more sense?


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## Devor (Mar 2, 2012)

OGone said:


> What I am trying to say is we can see Venus from Earth with a pair of binoculars (it appears as a star otherwise). Imagine nine planets, perfectly spread out and lined up while moving in unison along the same orbit as Venus. Imagine they are moving slower than Earth so that Earth can bypass them and line up perfectly with each one every 40 days... Does that make more sense?



Nine planets, evenly spaced, on an orbit that's parallel to Earth's.  They're on an outer-ring, Earth an inner ring.  The planets circle earth so that one appears in the sky at a time.

I can see why that should give you a regular cycle, but it would only ever equal one planet a month if the planets weren't moving.  Nine planets, nine months, exactly one year rotation.  I could be mistaken, but since they are moving, it seems to me like it _could not_ equal one a month no matter the distance.  If they're not moving, there would always be a monthly cycle, although multiple planets would be visible if the distance isn't right.

If the planets are moving and you line them up at a distance so that one is visible at a time, there's a fixed rotation cycle.  An astronomer could calculate how long each planet planet would be visible for.  It wouldn't be one a month.

That's very technical, though.  I don't know if many readers would even try to line them up in their head.  You could maybe do it and hang some kind of a lampshade on it.  Depending on what you're actually doing, and how well you actually attempt to explain it, you might still get away with it.  Someone else can opine on that one.  Having already lined them up, I'm in no position to answer that.


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## OGone (Mar 2, 2012)

Devor said:


> Nine planets, evenly spaced, on an orbit that's parallel to Earth's.  They're on an outer-ring, Earth an inner ring.  The planets circle earth so that one appears in the sky at a time.
> 
> I can see why that should give you a regular cycle, but it would only ever equal one planet a month if the planets weren't moving.  Nine planets, nine months, exactly one year rotation.  I could be mistaken, but since they are moving, it seems to me like it _could not_ equal one a month no matter the distance.  If they're not moving, there would always be a monthly cycle, although multiple planets would be visible if the distance isn't right.
> 
> If the planets are moving and you line them up at a distance so that one is visible at a time, there's a fixed rotation cycle.  An astronomer could calculate how long each planet planet would be visible for.  It wouldn't be one a month.



Maybe not on our planet, but could you make it last a month by interchanging the speeds at which the planets are orbiting? The planets need to be moving as I've never heard of a static planet. The planets don't circle "Earth", they circle the sun just on an orbital line further away. Say each planet is 20 "days" away from each other and they move at half the speed of Earth (the further away the planet is from the sun the slower they orbit in my knowledge) then it would take the Earth 40 days to pass one of the planets, right? 

Also I refer to all of our measurements of time - seconds, minutes, hours, days but they are completely ambiguous. A day on my World could be 2.7 days on ours for all the reader knows.

The Earth could then be tilted at an angle where the planets are visible, only in the night as to view them from Earth it would need to be facing away from the Sun (then the light would shine off of the planet, like our moon). That would also grant the "moon" its own lunar cycle as the Earth moves slowly out of line with the planet and onto the next one. 

Very confusing stuff but I think it would make sense, but perhaps I'm wrong...


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## Devor (Mar 2, 2012)

OGone said:


> Maybe not on our planet, but could you make it last a month by interchanging the speeds at which the planets are orbiting? The planets need to be moving as I've never heard of a static planet. The planets don't circle "Earth", they circle the sun just on an orbital line further away. Say each planet is 20 "days" away from each other and they move at half the speed of Earth (the further away the planet is from the sun the slower they orbit in my knowledge) then it would take the Earth 40 days to pass one of the planets, right?



I'm going to stick with it _could not_ equal one a month.  I don't know how close it can get to one a month, but that's the one number I'm confident it could not be based on the information you've provided.

The earth circles the sun yearly.

There are nine planets, and nine months.  If the planets do not move, that's one a month.  That seems clear.  Done.

If the planets move, I believe you cannot align them so that each passes the earth once per year for one a month.  If they moved at half the speed of earth, then earth would cross each planet twice a year.  Think of race cars on a track.  If you move at half the speed, how many times do you get lapped?  That may not seem like an appropriate comparison at first glance, since cars are moving at different speeds on racetracks of different lengths, but that can be _normalized_ so that you're measuring speed based on arch length traveled and the comparison becomes relevant.  (Admittedly you were referring to a different measure of speed, so the 2 years comment isn't exactly right.  Still, the point holds.)

Your spacing of 20 days is arbitrary; they would pass once a month, and then leave a long span of darkness before they returned because they aren't spaced evenly.  Maybe that's something you can work with?  One year of monthly planets, followed by a year of blackout?


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## OGone (Mar 2, 2012)

Devor said:


> I'm going to stick with it _could not_ equal one a month.  I don't know how close it can get to one a month, but that's the one number I'm confident it could not be based on the information you've provided.
> 
> The earth circles the sun yearly.
> 
> ...



I was thinking the year on this Earth though will be purely based on the lunar cycle though, this is where we're getting muddled. It doesn't matter where the planet is in regards to the sun because there are no seasons on the planet, I've took out the tilting back and forth towards the sun so there is no Northern or Southern hemisphere and no Winter or Summer assuming the orbital path has no ellipticity or eccentricity. The actual position of the planet in orbit means nothing because the weather is not affected so a year is purely derived from passing each of the nine moons rather than a year being defined as how long it takes to cycle around the sun once as with our year.

So the "Earth" could cycle past each of the nine planets a number of times before it fully orbits the sun and equals one of our years, but it moving round the sun is irrelevant because nothing changes so it could be anywhere as long as it is still passing the planets at a regular interval.

Just don't consider any scale or units of time / measurement. The nine planets are spread out perfectly equal distance away from each-other among their own orbit so I don't see how the blackness will happen?


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## Devor (Mar 2, 2012)

OGone said:


> I was thinking the year on this Earth though will be purely based on the lunar cycle though, this is where we're getting muddled. It doesn't matter where the planet is in regards to the sun because there are no seasons on the planet, I've took out the tilting back and forth towards the sun so there is no Northern or Southern hemisphere and no Winter or Summer assuming the orbital path has no ellipticity or eccentricity. The actual position of the planet in orbit means nothing because the weather is not affected so a year is purely derived from passing each of the nine moons rather than a year being defined as how long it takes to cycle around the sun once as with our year.
> 
> So the "Earth" could cycle past each of the nine planets a number of times before it fully orbits the sun and equals one of our years, but it moving round the sun is irrelevant because nothing changes so it could be anywhere as long as it is still passing the planets at a regular interval.
> 
> Just don't consider any scale or units of time / measurement. The nine planets are spread out perfectly equal distance away from each-other among their own orbit so I don't see how the blackness will happen?



It doesn't matter because they're still orbiting the sun.  One lap around the racetrack is one circle around the sun.  The nine planets are still spaced _evenly around the sun_.  The question is still _how often do the planets get lapped?_

I don't know how else to explain it.  Maybe someone else can pitch in.


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## Benjamin Clayborne (Mar 2, 2012)

So the inner planet is on its own orbit, O1; the other nine planets share an orbit, O2, farther out. The planets in O2 are spaced evenly around the sun, every 40Â°. (I'm not actually sure whether this would work; I believe that this is not gravitationally stable and any bodies in this orbit would either collide, forming a larger mass, or settle into the L4/L5 Lagrange points; but this only works if the masses at L4 or L5 are no more than 1/25 the mass of the primary orbiting object.)

So let's say you ignore that, and have nine objects of roughly equal mass orbiting in O2. O1 and O2 have to be far enough apart that the inner planet and outer planets don't throw each other off. However, to be far enough apart for this to happen, there would by necessity sometimes be two of the outer planets visible from the inner planet at the same time, on opposite ends of the same sky. You'd see one of them above the horizon in the west, and the other above the horizon in the east at the same time. Each one would undergo apparent retrograde motion for a short time as it was lapped by the inner planet, the same way that Mars, Jupiter, Saturn, Uranus, and Neptune all do to us here on Earth.

Honestly, unless your characters are going to be flying around on spaceships, I wouldn't worry about it. Just say that there's a ring of nine bright celestial bodies that take turns passing through the sky. If these people are worshiping planets as gods, they're likely not spacefaring, or particularly bright astronomers.


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## Butterfly (Mar 3, 2012)

What you have is a good idea but I think it is overcomplicated with too many factors that you will need to take into account by the presence of these planets - tides, gravitational pulls on other planets and their moons, planetary collisions. E.g, planets move at different speeds, so the fastest will eventually swallow up anything in its path and gravity will keep them in place as moons if they don't collide first. Take a look at Jupiter for an example of this. 

You could simplify it by looking at the real world. We all have star signs attributed to our month of birth when a particular constellation is highest in the sky. Perhaps you are imagining planets when they could really be constellations. 

I don't know how this would fit in with your world, but it's just a suggestion for you.


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## Queshire (Mar 3, 2012)

It''s fantasy, so long as it's internally consistent I doubt people are going to look too far into it.


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## OGone (Mar 4, 2012)

Benjamin Clayborne said:


> So the inner planet is on its own orbit, O1; the other nine planets share an orbit, O2, farther out. The planets in O2 are spaced evenly around the sun, every 40Â°. (I'm not actually sure whether this would work; I believe that this is not gravitationally stable and any bodies in this orbit would either collide, forming a larger mass, or settle into the L4/L5 Lagrange points; but this only works if the masses at L4 or L5 are no more than 1/25 the mass of the primary orbiting object.)
> 
> So let's say you ignore that, and have nine objects of roughly equal mass orbiting in O2. O1 and O2 have to be far enough apart that the inner planet and outer planets don't throw each other off. However, to be far enough apart for this to happen, there would by necessity sometimes be two of the outer planets visible from the inner planet at the same time, on opposite ends of the same sky. You'd see one of them above the horizon in the west, and the other above the horizon in the east at the same time. Each one would undergo apparent retrograde motion for a short time as it was lapped by the inner planet, the same way that Mars, Jupiter, Saturn, Uranus, and Neptune all do to us here on Earth.
> 
> Honestly, unless your characters are going to be flying around on spaceships, I wouldn't worry about it. Just say that there's a ring of nine bright celestial bodies that take turns passing through the sky. If these people are worshiping planets as gods, they're likely not spacefaring, or particularly bright astronomers.



Would it be possible instead of constellations just have planets far away which are so large they are visible as moons? Would that be feasible and could each planet still only appear for 40 days? 

I guess I could just go with the ring idea as it is *possible*, just explain the nine celestial bodies appearing and not go into too much detail and let it be a topic of discussion. If somebody can figure out a way in which it could work, great! If they can't then I will go back on myself and say "it's magic"


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## Steerpike (Mar 4, 2012)

Using "it's magic" to explain this sort of thing of thing is a poor way of going about things, in my view, unless you are going for a work in which all physical laws are suspect at their most common level. Even in Fantasy worlds, readers assume, rightly, that gravity works as expected, water runs downhill, fire is hot, and so on. Fundamental things. If magic in your universe is operative on a level that would negate something like gravitational effects of bodies in the solar system, then I think you have to establish that with the reader and play out the logical effects of such extreme magics on your world.


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## OGone (Mar 4, 2012)

Steerpike said:


> Using "it's magic" to explain this sort of thing of thing is a poor way of going about things, in my view, unless you are going for a work in which all physical laws are suspect at their most common level. Even in Fantasy worlds, readers assume, rightly, that gravity works as expected, water runs downhill, fire is hot, and so on. Fundamental things. If magic in your universe is operative on a level that would negate something like gravitational effects of bodies in the solar system, then I think you have to establish that with the reader and play out the logical effects of such extreme magics on your world.



In that case it looks like the constellations are the way forward, but again would it be possible to have constellations which operate on a 40 day cycle? Perhaps I could just have one larger star (potentially coloured?) to represent the Gods instead of a planet?


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## Benjamin Clayborne (Mar 4, 2012)

OGone said:


> Would it be possible instead of constellations just have planets far away which are so large they are visible as moons? Would that be feasible and could each planet still only appear for 40 days?



No. Any planet that large would collapse into a star.

I'm going to short-circuit this conversation and ask why it's so important that the astronomy in your story works this way. Is it for some important story reason? Or is it just because you like having a nice, neat, symmetrical setup? If it's the latter, I'd say ditch it and stick with a more Sol-like system. The natural world is not nice and neat; our ancestors got along just fine with having a variety of planets that had different orbits. Resist the urge to make things simple and easy; it won't make your story any better.


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## OGone (Mar 4, 2012)

Benjamin Clayborne said:


> No. Any planet that large would collapse into a star.
> 
> I'm going to short-circuit this conversation and ask why it's so important that the astronomy in your story works this way. Is it for some important story reason? Or is it just because you like having a nice, neat, symmetrical setup? If it's the latter, I'd say ditch it and stick with a more Sol-like system. The natural world is not nice and neat; our ancestors got along just fine with having a variety of planets that had different orbits. Resist the urge to make things simple and easy; it won't make your story any better.



It is not integral so much, I just like attention to detail and wanted the origins of the main religion (being the belief of eleven gods) to originate from somewhere and I thought planets or stars up in the sky representing the Gods would be a good way to stem the inhabitant's beliefs from somewhere. 

The astronomy itself isn't important, I'm never actually going to explain the formation of the solar system. Just if I did have recurring planets / stars in the sky I wouldn't want somebody to read into it, picking it apart and stating it impossible even if it is a fantasy story (because as Steerpike mentioned I still want to retain the same rules and laws of gravity as in real life).


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## Steerpike (Mar 4, 2012)

I think you have to satisfy the average reader's sense of verisimilitude. If you had a number of small moons orbiting the planet, the average reader is going to know enough about tides to wonder what the effect would be. If you have action of the story taking place in and around the sea, you should have an explanation for how the moons affect the tides. Much beyond that, if you're writing fantasy the reader isn't going to need the details (and in many cases won't want them), so I wouldn't say a whole lot more unless you come across another glaring issue where the moons would have an impact.

Same thing with regard to planets. And in the case of planets, even fewer people would expect many physical effects on your world.


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## Caged Maiden (Mar 4, 2012)

I your goal is just worshiping eleven gods, there are other ways to make that happen..... Say ancient people found eleven places of power, or your one moon has eleven "seas" or even that there are eleven holy trials, or eleven "virtues" of holy people..... I like the idea of having stuff mean stuff, but it is a very modern idea.  

If the religious leader says that now a month has thirty days, then it does.  If he decided next year that there is an extra month in the year, and each month is now twenty-six days..... well people wouldn't riot over that sort of thing.  They just kept doing what they do and get on with life.  After all..... religion set most of the rules.

I would recommend thinking about what's important to your people, then asking what's feasible.


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## Caged Maiden (Mar 4, 2012)

Just another thing to consider..... I once went to a con, and there was a man selling his self-published book.  He had a similar, but completely unrelated thing like this in his own book, and in his pitch to sell me his book he went into great detail about his own very creative idea he invented.  Unfortunately, by the time he'd finished going through all the wonderfully creative scientific explanations... my friend and I were ready to mace him and run away.  It was too much to want to hear about and I'm convinced that the only reason he went on and on like that was because he'd received some criticism which had pushed him to continue to elaborate to make his idea more feasible.

I'm no astronomer, but I have a friend who is.  If you want me to ask him whether this sort of thing is feasible, send me a PM and I'll ask him.  If the important thing is for your people to develop a religion based on eleven gods..... You might think about an easier-to-explain reason.  I started a thread a while ago about inconsistencies from lack of research, and I can't emphasize enough how frustrating it is to read something which you know is impossible.  It just feels like a let-down, like someone didn't care enough to put in the time for accurate research.

I'd hate for you to get frustrated trying to make the pieces fit together if they just can't, and in the end, you should feel proud of what you have created.


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## Devor (Mar 4, 2012)

Steerpike said:


> Much beyond that, if you're writing fantasy the reader isn't going to need the details (and in many cases won't want them), so I wouldn't say a whole lot more unless you come across another glaring issue where the moons would have an impact.



This.  I think, honestly, this is one of those times where a vaguer answer makes sense.  Astronomy is a complicated science, and really answering the question involves mathematical abstractions, even if it can somehow be made to work.  This is literally the sort of question for which calculus was invented, and saying too much about it is going to highlight any mistakes you might be making in putting your system together.  Unless there's some reason the exact model of your solar system is needed, I would just hang a lampshade on it and move on.


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## Fnord (Mar 5, 2012)

Actually mapping this all out will take a lot of advanced math relating to orbits, axial tilt, the speed of rotation, etc to see if it's feasible; a lot more work than most readers would certainly bother with.  If George R.R. Martin can make a world where summers and winters can last a decade without having to explain how things like crop management can actually occur (just ask any horticulturist what the consequences of no regular winterization would do), or the fact that Krynn from the Dragonlance books can have three moons without extreme tidal effects (since the moons are often portrayed as being in the sky overhead often simultaneously and thus on the same side of the planet at the same time), you're probably safe with the "one planet a month in the sky".

I understand your desire for physical consistency (I'm a stickler myself), but you're probably going to be the only one who really cares in the end.


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## Devor (Mar 5, 2012)

Okay, I think I figured out how it could work.

There are situations in the universe where two stars orbit each other.  If Earth is orbiting one star, and the nine planets are orbitting the other star, _I think_ you should be able to make it work.  The two orbits would have to be perpendicular to each other, so that Earth would always have a clear view of the second star and whatever planet is "up next" in the order.  Since the planets are moving closer to, then further from, the earth, you could even avoid having two visible at once.

Of course, now you'd also have a giant star in the sky.


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## Steerpike (Mar 5, 2012)

Maybe the second "star" is a small black hole with enough pull to have planets orbiting it, but not enough to suck everything in for a few million years. Then you won't have a blazing star in the sky.


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