Alternative world questions for a fantasy story

Hey.
I’ve asked this question before (long, long ago) and I’ve forgotten the answera. So, anyway, those of you that have a knowledge of astronomy/physics, can you answer this?

I’m writing a fantasy/fiction story that takes place on another world. The problem is that I’m trying to get all the little details right–after all, god is in the details–and I have almost no knowledge of physics or astronomy. :smack:
Anyway, here’s the info I’ve made up so far:

Athereal is the fifth planet in the solar system of seventeen and is the twelfth largest. It is the only planet in the solar system that contains both active plate tectonics and liquid water. It rotates clockwise (thus the sun rises in the west and sets in the east) and its orbital period is 237.98 days. It has no axial tilt. Average person lives to be 107; old age is 140. Children are considered adults around the age of twenty-six. It has two moons, one like Earth’s, and another that’s close to the southern hemisphere of the planet and cannot be seen from the northern. (I’ve read that Mars is like this, yet I can’t remember the scientific title for it.)

So here’s the list of questions:

To the best of my understanding, with no axial tilt, there would be no seasons; temperature and climate would be dependant upon lattitude (i.e., always cold near the poles, a desert wasteland at the equator, leading to a large pupolation difference between the temperate zones and the extremes). Is this correct?

How would evolution occur? Those in the north would obviously have evolved to be hardier to the cold–shorter bodies, more fat, perhaps with blond hair, while those near the equator would be darker, skinnier, perhaps with the ability to hold water for long periods of time. Does that sound right?

How would tides be affected with two moons? Assuming one orbits like our moon (on a monthly cycle), and the southern moon on a weekly cycle, would the tides be terribly affected in the northern hemisphere? What about the south?

How would weather occur? With no tilt, and the sun striking the planet at a fairly even rate, could storms (with few expections) be “scheduled?” They would obviously come in from the east in the temperate zones, much like they come in from the west in ours (I believe, due to prevailing winds). But I’m not sure if they could be a regular phenomena.

Well, that’s all I have for now. If I come up with any more questions though the course of the story, I’ll bring them up. And thanks in advance for racking you brains on this one. I promise a dedication to the geniuses at the SMDB. :smiley:

Many typos abound. Sorry. :smack:

IANAA (I am not an astronomer), but is it really possible to have a natural satellite that is only visible from the southern hemisphere? I think a satellite has to orbit around a planet’s center of mass, not (necessarily) its polar axis.

You could have a satellite in a “stationary” orbit around the equator, so only half the planet would ever see it, but that would be visible from half the north hemisphere and half the south.

I could be wrong, but I’m having trouble visualizing the orbit you’re describing.

Physically impossible. The plane of the moon’s rotation has to pass through the center of the planet, so both north and south hemispheres will be able to see it at times. It might be in an elliptical polar orbit that spends more time over one hemisphere than the other, but it can’t spend all it’s time only over the southern half of the planet.

No seasons, correct. However, placement of mountains and oceans will affect local weather patterns, so climate will depend on more than just lattitude. Unless your planet’s orbit is perfectly circular, there might be mild seasonal variations as the distance to the sun changes over the course of the year. The sun may have variable output over time - our sun has an 11-year cycle of activity, and may have been more variable than it is now from time to time. It’s also possible that there might be long-term climate cycles not related to the time of year.

This is really hard to say - evolution is a complex and non-predeterminable process. It will depend heavily on interactions with the local microclimates and ecosystem - those living near the equator might not need to evolve to conserve water if they live in a tropical rain forest, for example.

I’d doubt it. Even without seasons, the atmosphere is a complex, chaotic thing. It might be possible to predict a major storm every 2 weeks or so, but you’ll sometimes get one coming a week ahead or behind of scheduel.

Polite Objection:

There would be no free liquid water!

It would all wind up frozen in the poles, carried there by storms. With no axial tilt, icebergs wouldn’t melt & break free.

Possible scene–volcanic eruption under the icecap! Result- dramatic steam explosion! :eek:

My advice: forget making it “scientific” and concentrate on writing a good story. Don’t call attention to these details and just write what’s happening.

Remember, the Ringworld is unstable, Mesklin can’t work, and Mars doesn’t have princesses. But that didn’t stop Niven, Clement, and Burroughs from writing classic novels about them.