Collaborative Conworld

[Lyhoko Leaci]

A bigger gas giant can generate larger moons, or a planet could be captured by a gas giant as it migrates though the solar system. (Though the second option there would mess up any other moons it had to begin with)

I believe that a moon with a day length of similar length as an Earth day should be possible, especially with a heavier than Jupiter gas giant. On another note, a heavier than Jupiter planet would still be similar in size to Jupiter.

[KathTheDragon]

Though make it too heavy and you get a brown dwarf, and thence a binary star system.

[kanejam]

I thought that most moons don't have a flat orbit i.e. they aren't eclipsed by the planet during their day? Or at least there are long periods of time when said moon is full that it is receiving plenty of sunlight. What are the constraints on moon orbits? Can you get it so that the moon would get enough sunlight on all faces and there wouldn't be too great a disparity between the sunlight received on one side as on the other? Another reason against a gas giant moon is that it's too far from the sun for life.

Unless there is the possibility of pleasant conditions on a moon I vote either planet with several (large) moons or double planet system.

[Lyhoko Leaci]

I thought that most moons don't have a flat orbit i.e. they aren't eclipsed by the planet during their day? Or at least there are long periods of time when said moon is full that it is receiving plenty of sunlight. What are the constraints on moon orbits? Can you get it so that the moon would get enough sunlight on all faces and there wouldn't be too great a disparity between the sunlight received on one side as on the other? Another reason against a gas giant moon is that it's too far from the sun for life.

Unless there is the possibility of pleasant conditions on a moon I vote either planet with several (large) moons or double planet system.

A moon can be orbiting at an angle, which would cause the eclipses to be limited to two parts of the year, this would also cause the moon to have seasons like Earth. (Eclipses would be in spring/fall) Even without that, the moon would still get plenty of sunlight on all parts.
Gas giants can be anywhere in a solar system. Just because they're too far away from the sun for life in our solar system doesn't mean they'll be that way elsewhere.

[kanejam]

Well in that case a moon could be cool. The frequent eclipses could have some interesting effects on mythology. One last question though; wouldn't one face of the moon only face the sun when on the far side of the planet, meaning it's further from the in than the other side? Would this produce a noticeable difference?

Edit: This is assuming it's tidal-locked. Does it need to be?

[Lyhoko Leaci]

Well in that case a moon could be cool. The frequent eclipses could have some interesting effects on mythology. One last question though; wouldn't one face of the moon only face the sun when on the far side of the planet, meaning it's further from the in than the other side? Would this produce a noticeable difference?

Edit: This is assuming it's tidal-locked. Does it need to be?

Yes, it would be farther away, but the distance difference caused by the moon's orbit is about 1% of the planet's orbital radius, if that, assuming the moon orbits at a similar distance to its planet that Io does, and the planet is at the same distance from the sun that Earth is. This shouldn't make that much of a difference.
(149,598,261km Earth orbit radius, 421,700km Io orbit radius)

If the moon's not tidally locked, then the eclipses would not be in the same place and time, and everyone would see the planet, and the average distance from the sun during the day would be the same for the entire planet. However, the tides would be massive, and would cause their own problems. The moon would also probably become quickly tidally locked.

[Torco]

Edit: This is assuming it's tidal-locked. Does it need to be?

I think yes; if it wasn't tidally locked it'd be a pretty new addition to the big ass planet's system and while bacteria seemed to pop up quick on earth, there's the anthropic thing and also bacteria don't make conworlds good at having conlangs and stuff.

[Sacemd]

I think we have now agreed a gas giant moon could be pretty earth-like aside from a thing floating in the sky on one side of the planet.

Another question: how would the other moons of the gas giant appear in the sky?

[KathTheDragon]

Somewhat like the planets do to us.

[Torco]

all over the place xD

[Lyhoko Leaci]

Any other major moons could be seen as being round, though mostly smaller than our own moon. They would behave somewhat as the planets do in our own sky (traveling in roughly the same line), aside from moving much faster and being a lot bigger looking. Intermediate size moons might be visible as being round if you're lucky (and they're in a part of their orbit where there near the habitable moon) and would most likely follow the same line as the major moons. Any minor moons (of which there's bound to be quite a bit) could have odder orbits and could potentially appear anywhere in the sky, though some could follow the same line as the major moons. They would appear like bright dots. Or not so bright dots for the farther out ones.

Any visible rings would be in the same plane as the major moons, and would just be visible as a thin line. The ring's shadow on the planet, however, would be easily visible.

[Hallow XIII]

Any other major moons could be seen as being round, though mostly smaller than our own moon. They would behave somewhat as the planets do in our own sky (traveling in roughly the same line), aside from moving much faster and being a lot bigger looking. Intermediate size moons might be visible as being round if you're lucky (and they're in a part of their orbit where there near the habitable moon) and would most likely follow the same line as the major moons. Any minor moons (of which there's bound to be quite a bit) could have odder orbits and could potentially appear anywhere in the sky, though some could follow the same line as the major moons. They would appear like bright dots. Or not so bright dots for the farther out ones.

Any visible rings would be in the same plane as the major moons, and would just be visible as a thin line. The ring's shadow on the planet, however, would be easily visible.

So, in effect, the sun would become a relatively minor object in the sky. And therefore be much less prone to becoming the supreme deity (bar the conworld having physical gods). This is innovative, so I second that. It also creates much less of a gravitational (and therefore calendar) mess than twin planets, so I vote gas giant moon.

[KathTheDragon]

Definitely for the side of the moon facing the planet, the planet itself would represent the supreme deity. The sun would either be the second deity, or the wife of the planet. For the other side, the sun would probably still be the supreme deity, being the most regularly appearing object.

[Lyhoko Leaci]

It seems that a moon of a gas giant is the most popular option here:

Moon of a gas giant:
sacemd, kanejam?, Lyhoko Leaci, Hallow XIII

Double planet system:
KathAveara

Single planet:
...

Some more decisions:
What should the moon's geography be like?
Archipelago-like: Many small, scattered "continents," few, if any, deserts
Land-locked sea(s): many deserts, scattered green areas near the sea(s)
Pangaea: just one continent, deserts in the center, greener around the outside
Continents: More like Earth

How big should the moon be?
Small (80-95% smaller than the Earth): Low-ish gravity, taller life and mountains
Earth sized (95-105% the size of Earth): Earth-like gravity
Large (105-120% larger than the Earth): High-ish gravity, shorter life and mountains

What should the day length be?
22-28 hours, mostly Earth-like
28-36 hours
36-48 hours, long, but reasonable
48+ hours, quite long, but with a thicker atmosphere, should be tolerable. Note this will change the biomes available quite significantly.

What sort of other moons should there be?
Several other large moons, a few or no intermediate moons (Like Jupiter)
Just one other large moon, several intermediate moons
No other major moons, but multiple intermediate moons (Like Saturn)

Note that all options assume a significant amount of smaller moons, probably around 2 dozen.
By major moons, I mean moons that are comparable in size to our own moon or larger. Intermediate moons are moons that are big enough for their own gravity to make them round, but are noticeably smaller than our moon. Minor moons are ones that aren't big enough to be round.
More details about the rest of the system will be decided after voting on the general layout.

I am assuming a gas giant of around 4 to 6 times the mass of Jupiter, which should be able to have an Earth-sized moon, but is still well below the brown dwarf transition (at around 13 Jupiter masses)
The gas giant itself would have mostly white (water-based) clouds.

[Sacemd]

On the other hand, the sun is still the thing that brings life (lengthening of days = spring). As such, it is very likely the life-giving deity, probably a female one. One of the myths could be that the planet god eats the sun goddess which is reborn later (reflecting the frequent eclipses). Or the sun god is male, impregnates the planet goddess, is then killed for some reason (probably killed or eaten by his own wife) and then reborn as his own son.

[Sacemd]

I vote for continents, earth-like gravity and day length (I know, it's slightly boring)

I don't really care for what kind of other moons we'd have, but seven visible moons of significant size would be cool (Just because I like seven for symbolic reasons. Or four. Four is also a nice number).

The planet being white is a nice touch to the religions on the planet-side: given the yellow star the two (probable) main deities would reflect the dualism of Gold and Silver.

[KathTheDragon]

I vote for small moon/weak gravity. I also second 7 principle other moons. 'Tis my favourite number. I would also propose a white A-type star. This necessarily moves the hot Jupiter further out, and lengthens its year.

[kanejam]

I'm voting for gas giant moon.

Smaller than earth so lower gravity and volume with a small reduction in surface area. Maybe either four or seven other large moons, if seven then we could have one slightly bigger than our own moon, there's no reason that we have to be the biggest.

I'm not too fussed about geography although I do like islands and archipelagos, but a moon with earth-like continents would be bound to have plenty of islands anyway.

Edit: also not too worried about day length, anything from 22-36 is reasonable.

[Sacemd]

I would also propose a white A-type star. This necessarily moves the hot Jupiter further out, and lengthens its year.

Yes... but here again the colour thingy and the short life of white stars may cause problems.

[Hallow XIII]

I would also propose a white A-type star. This necessarily moves the hot Jupiter further out, and lengthens its year.

Yes... but here again the colour thingy and the short life of white stars may cause problems.

Do we have exotic physics (e.g. magic)? Cause then the short life can be circumvented.

[Rodlox]

I would also propose a white A-type star. This necessarily moves the hot Jupiter further out, and lengthens its year.

Yes... but here again the colour thingy and the short life of white stars may cause problems.

the important thing is that there are people there during the star's lifetime, not how they got there, right? (just ignore the "how'd they get there?" part, and go to the next step)

[KathTheDragon]

I would also propose a white A-type star. This necessarily moves the hot Jupiter further out, and lengthens its year.

Yes... but here again the colour thingy and the short life of white stars may cause problems.

It doesn't necessarily have to be a big A-type star. One on the cooler end, borderline F-type. Certainly nothing approaching B-type. Actually, just done a little searching around, and I downgrade my proposal to F-type. My books give the 'conventional colour' according to Wikipedia.

[Lyhoko Leaci]

Using an equation I found that calculates star lifetime based on mass, the rough lifetimes for various star classifications should be the following (using masses from wikipedia):

A
1.6 to 4.3 billion years

F
4.3 to 10 billion years

G
6.3 to 17.5 billion years

K
13 to 35.9 billion years

M
35.9 billion years to 6.5 trillion years

Theoretically, an F type star, even a brighter one, could have intelligent life, if life is quick to develop from single cells to multi-celled.

Or if aliens seeded life there, or there's magic that lengthens star lifetime somehow...

[KathTheDragon]

So, we could quite easily have a nice F5 star there.

Edit: I've actually got an F6 star for one of my con-worlds.

[Lyhoko Leaci]

According to the chart I found here: http://www.world-builders.org/lessons/l ... ables.html an F5 star would have 1.400 times the mass of the sun, 1.440 times the radius of the sun, 3.2 times the luminosity of the sun, a habitable zone at around 1.79AU (for an Earth-like planet), and a lifetime of 3.440 billion years.

Using the same equation that I used in the previous chart (Lifetime = (M/L)*10 billion years), where M = mass and L = luminosity = M^3.5. (so Lifetime = (1/M^2.5)*10 billion years), an F5 star has 1.2 times the mass of the sun, 1.89 times the luminosity of the sun, a habitable zone at around 1.37AU (for an Earth-like planet) and a lifetime of 6.34 billion years. (This roughly corresponds with F8 on the other chart) Equation: http://hyperphysics.phy-astr.gsu.edu/hb ... rtime.html

Both would have more UV light than the Earth, so watch out for sunburns.