[Space] Adapting to long days and other implications of a generated system

[Agemegos]

Originally Posted by Diomedes

That's what I meant; the oceans inline with the other planet will be at a permanent high tide. Any oceans on the orthogonal meridians will be shallower. And since the planets are larger and nearer to each other than the moon, they'll be very large tidal forces.

Yes, but the bulk of the planet will be at permanent high tide there too. And since it is permanent in geological terms, the mantle material will have the necessary tens of thousand of years to conform fully to the tidal equipotential. The water and the rock will be distorted to the same extent, they will conform to the same geoid. So the oceans will be about the same depth all over. Slightly deeper where the net effective gravity is lower, perhaps, but not enough so to produce vast oceans around sub-lunar point and its antipode and vast continents on the orthogonals.

[Agemegos]

Originally Posted by Bruno

The water will deform more and faster than the planets main mass will, so it's still going to be deeper on the side of the planet facing the partner, shallower on the sides, and then deeper again (but not as deep) on the far side of the planet.

It doesn't matter that the mantle material deforms more slowly than the water, because the tidal bulge never moves. It stays in exactly the same spot for millions and millions of years, whereas it only takes tens of thousands for mantle deformation to reach equilibrium.

Slower deformation doesn't mean less deformation. Both rock and water reach equilibrium in a geologically brief time, and it is the same equilibrium for both.

[Indigar]

OK, your replies have given me some more food for thought.
I've been doing some more number crunching, and have worked out some of the social details and such.

Firstly, because the planet's axial tilt is so low, seasonal variations will be very mild. I checked whether the companion star's large orbital excentricity, and thus the large difference in distance to the planets during its orbit would cause seasons, but even at closest approach its contribution to the planets' temperature is negligable.

So, I've come up with the following:
The calendar is based on a year of 66 days; this is devided into the four seasons/months: Spring of 17 days, Summer of 16, Autumn of 17 and winter of 16; every 10th year is a leap year, when the last day of Winter is dropped, and once every 40th year, when this day is _not_ dropped.

Longer-duration temporal cycles are based on the orbit of the companion star (which takes 16.76 local years):
The years are grouped into Cycles of 17 or 16 years: Three cycles of 17 years followed by one of 16 years; four of these cycles make a Great Cycle of 67 years.
And, 25 Great Cycles make a Grand Cycle; the last Cycle of the last Great Cycle of a Grand Cycle is once again 17 years instead of 16. Thus, a Grand Cycle is 1676 years.
The current dominant society does not count the Grand Cycles; the counting of years begins at the beginning of the current Grand Cycle, when, according to tradition, the Voice of the Gods began his ministry (This is counted as the beginning of the dominant religion).
At the beginning of the campaign, it is the 13th day of Spring of the 1321st year, or as it is usually described, the 13th of Spring of the 14th year of the 3rd Cycle of the 20th Great Cycle since the Proclamation of the Gods (Short form 13 Spring 14:3:20).

I think this is a system that is simple enough, but also different enough to give the flavor of a different world.

Other stuff:
The day is divided into 100 local hours, each of which is slightly shorter than an Earth hour. Hour 0 or 100 is at sunrise.
In the area in which the campaign begins, the Sister planet is above the horizon. This means that, each day about 10 hours before sunset, there is an eclipse of the sun lasting about 10 minutes, and an eclipse of the Sister about 10 hours before sunrise. In addition, there is an eclipse of the Companion star, the time of which depends on the progress of the current cycle; currently, it falls about 10 hours before midnight.
The normal sleep cycle is 33 hours awake, 17 asleep; therefore, there is one full sleep/wake cycle during each of night and day. By tradition, people go to bed around the time of the eclipses of the Sun and the Sister.

In mythology, the Sun is the Mother Goddess, and stands for life, fertility, etc. The Companion is the Father God, and stands for law, order, civilisation, etc. The Sister is the literal Sister of the world, and is said to have angered the Father and the Mother shortly after Creation; because of this, it receives only little warmth from the Mother. During the fallen Empire attempts were made to colonise it (over the objections of the Church), but there is no longer any contact with it. (It is still inhabited, but only sparsely, and its TL has fallen to 2).
The dominant religion recognises two gods, the Mother and the Father. Each of these has its own seperate Church (the Mother church ordains mostly women, the Father church mostly men), but these are closely allied (though they do not always agree on all issues), together forming the Joined Church.

Well, that was what I've written down so far. It's mostly random thoughts that I've worked out about this system, but I'll develop it some more later.

Any further comments?

[Agemegos]

Originally Posted by Indigar

Firstly, because the planet's axial tilt is so low, seasonal variations will be very mild. I checked whether the companion star's large orbital excentricity, and thus the large difference in distance to the planets during its orbit would cause seasons, but even at closest approach its contribution to the planets' temperature is negligable.

Did you check whether the eccentricity of the twin planets' orbit around their primary induces seasonal effects? I find that the GURPS Space star system generation sequence gives planets's orbits such high eccentricities that it is worth calculating surface temperature at perihelion and aphelion.

[Indigar]

Originally Posted by Agemegos

Did you check whether the eccentricity of the twin planets' orbit around their primary induces seasonal effects? I find that the GURPS Space star system generation sequence gives planets's orbits such high eccentricities that it is worth calculating surface temperature at perihelion and aphelion.

I didn't think to check this, since I thought an eccentricity of 0.05 was pretty low. I now see that Earth's eccentricity is 0.017, so that is indeed quite a bit higher.
I get a difference in BB temp of 14K due to excentricity, but I have no idea what effect this would have in real-world terms. I get 4K for Earth's variation, but I don't know how much difference 6 degree tilt versus Earth's 23 degree tilt makes; would this mean that this planet's seasons are more or less extreme than Earth's (assuming a point on the surface where tilt-seasons and eccentricity-seasons combined)?

[lwcamp]

Originally Posted by Indigar

Would it be more doable if I declared there to be a much higher percentage of oxygen? Since the atmospheric pressure is about 0.46 atm, could I simply double the oxygen percentage to 40%, or would that cause other effects.

The higher the percentage of oxygen, the easier things burn even if the partial pressure of oxygen is kept the same. At 40% oxygen, there's not likely to be much land life, with the land scoured by wildfires when even moderate amounts of biomass build up.

Luke

[tantric]

You know, GURPS abhors randomly generated characters - why would you randomly generate your world? I like the system you have, but you should certainly feel free to adjust it any way that pleases you - you have to live with it, after all. Does Space allow you to work backwards? Eg, I want dual planets, how does that change other factors?

[Flyndaran]

Originally Posted by lwcamp

The higher the percentage of oxygen, the easier things burn even if the partial pressure of oxygen is kept the same. At 40% oxygen, there's not likely to be much land life, with the land scoured by wildfires when even moderate amounts of biomass build up.

Luke

Or plants evolve to use it to procreate the way some trees do on earth.
Or plants evolve fire resistant coatings, so only dead brush blazes.
Animals evolve to run... the... h*ll away.
Animals evolve to dig deep fireproofe tunnels, seal the entrances, and go into suspended animation.

[Agemegos]

Originally Posted by tantric

Does Space allow you to work backwards?

Yes. It won't let you work backwards from tides or anything that is causally "downwind" from tides, such as day-length. But it will otherwise.

[thtraveller]

Originally Posted by Indigar

I get a difference in BB temp of 14K due to excentricity, but I have no idea what effect this would have in real-world terms. I get 4K for Earth's variation, but I don't know how much difference 6 degree tilt versus Earth's 23 degree tilt makes; would this mean that this planet's seasons are more or less extreme than Earth's (assuming a point on the surface where tilt-seasons and eccentricity-seasons combined)?

Average temperature variation for 6 degrees tilt is probably only 1 or 2 degrees (sunlight per unit area should be proportional to [1/cos tilt-angle] squared and 6 degrees tilt gives about [edit] a sixteenth of the variation that 23 degrees tilt does at the equator and about a 24th outside the tropics)

So including the 14 degrees for eccentricity you are looking at perhaps 16 degrees overall average annual temperature variation.

Its seasons will be more extreme near the equator than Earth's but less extreme overall. Earth's equator only sees the temperatures vary by single digit degrees. Whereas Earth's poles see something like a 30 degree variation over the year.

Earth does get a theoretical 4 degree temperature variation with it being warmest at perihelion around 4th January each year (southern hemisphere summer), though the oceans buffer the rise.