Apocalyptic Events, Super Volcano's, Gravity and Humanity...

[Ultrazen]

Hecate is further away from Midgard than our Moon to Earth but they exert roughly the same amount of gravitational force as the Moon does to the Earth, and Earth to the Moon. Hecate does not revolve around Midgard and does not rotate, causing one side of it's surface to be bathed in light constantly while the other to be constantly bathed in darkness. There is one continent on each side roughly 5 million square miles each. The oceans are not as deep as they are on Earth but are suitably deep enough to create a hydrosphere.

The whole sounds interesting.
A nitpick though... not sure how important your moon and realism is to your setting...

When you say it does not revolve around Midgard, you mean it always appears stationary in one spot in the sky? So it is always visible from your equivalent of north america but never anywhere else, for example? In fantasy, that's fine, you can handwave away geosynchronous orbit requirements. (This also does away with tides, by the way. You could still have them... they would just be caused by something (magic?) other than changing lunar gravitational forces.)

However, for also only one side of Hecate to always have sunlight and the other not, it must rotate. Earth's moon does not rotate - we always see the same side. During part of a month the side facing us is lit with sunlight (the full moon) and at other times its opposite side receives sunlight (the new moon). In order for only one side to receive sunlight, it would have to rotate some, meaning a "light" and "dark" side would at different times face the earth.

Same for your setup.

 

[grodog]

A very interesting thread!

For some additional resources on super volcanoes, I point you to the following resources:

On Super Volcanoes
The Yellowstone Volcano Observatory at http://volcanoes.usgs.gov/yvo/ in general, with specific articles at http://www.geotimes.org/current/feature_supervolcano.html and their FAQ at http://volcanoes.usgs.gov/yvo/2005/docudrama.html

For some good general reading about volcanoes, I recommend Volcanoes: Crucibles of Change at http://www.amazon.com/exec/obidos/t...103-1462853-8551834?v=glance&s=books&n=507846
and for the impact of a large eruption on local populations, I recommend Unearthing Atlantis : An Archaeological Odyssey by Charles Pellegrino (all about the eruptions of Thera/Santorini that may have inspired the Greek narratives of Atlantis) at http://www.amazon.com/exec/obidos/t...103-1462853-8551834?v=glance&s=books&n=507846
and Krakatoa: The Day the World Exploded by Simon Winchester, at http://www.amazon.com/exec/obidos/t...103-1462853-8551834?v=glance&s=books&n=507846

On Mega Earthquakes
I like Bruce Bolt's Earthquakes book for general info/history/etc. at http://www.amazon.com/exec/obidos/t...103-1462853-8551834?v=glance&s=books&n=507846
For some specifics about huge earthquakes, check out http://earthquake.usgs.gov/bytopic/megaquakes.html and for info about the New Madrid, Missouri earthquakes, see http://neic.usgs.gov/neis/states/missouri/missouri_history.html and http://neic.usgs.gov/neis/eq_depot/usa/1811-1812.html

On how to properly spin all of this info and figure out its effect on your planet, I recommend Martyn J. Fogg's Terraforming: Engineering Planetary Environments book (details on Amazon at http://www.amazon.com/exec/obidos/t...103-1462853-8551834?v=glance&s=books&n=507846 It's out OOP, but an excellent resource on planetary system dynamics. For a bit less technical view, you can always check out Expedition Retreat Press' A Magical Medieval Society: Ecology & Culture at http://www.rpgnow.com/product_info.php?products_id=2510&

I hope that helps some.

 

[Malanath]

Ultrazen-

Ahh. Damn, I was hoping I could just say Hecate revolves around the sun but was close enough to Midgard to act sorta like a Moon. I really wanted one side of Hecate to -never- face the Sun or receive any major light.

Of course I am leaning toward just making it work like the Moon, just have one side constantly facing the sun while the other never does. (Hey it's uhh... magic? ) No, seriously though I want to have fun with the Moon and make it somewhat different.

What I am ultimately trying to avoid is becoming the Wizard in the Wizard of Oz. I don't want someone who is experiencing my world to suddenly find "the man behind the curtain." Fantasy is after all about suspending disbelief if for only a short amount of time. If I can make things more believable then it enhances the ability to weave the tale. (Well at least from my prospective.)

grodog-
Thanks for all the links. I'm going to look into some of them.

 

[trancejeremy]

FWIW, the Sun also causes tides. Mostly the moon, but even without it, there would still be tides. IIRC, it's like 65-70% Moon, 30-35% Sun.

 

[Evilhalfling]

We have discussed population growth before and iI have even attempted to apply population growth calculations (used in city planning) but after 3000 -5000 years it basically comes down to handwaveing. The birth and death rates basically balance wherever ou want but dont take into account other disasters that would have occured since then. Cultures can move very quickly or slowly depending on countless factors.

 

[Ultrazen]

Ultrazen-

Ahh. Damn, I was hoping I could just say Hecate revolves around the sun but was close enough to Midgard to act sorta like a Moon. I really wanted one side of Hecate to -never- face the Sun or receive any major light.

Ohhh.
OK. Try this then, just as an idea.
Get out your favorite search engine and hunt down some info on Saturn's moons. Specifically the ones known as shephard moons (sorry, I don't maintain any list-o-links myself). These help keep parts of the ring system intact and at least two of them actually switch orbits from time to time. There's nothing to keep you from modeling something similar on a much larger scale, especially for a fantasy world. Is this more along the lines of what you are thinking about?

One other thing... planets and moons tend to "spin down" until there is no relative rotation. The planet Mercury always has one side facing the sun, for example, in the same way one side of the moon always faces the earth. So you have excellent precedence for Hecate's behavior.

I think there is a balance somewhere between realism and playable fun. I know in my own world the moon/tide system isn't quite accurate, but it's close if you don't think about it too much, and it's easy to track if someone wants to know something about lunar phases or when the tide is coming in or whatever. As some point in a fantasy world, deviations from reality cease to be errors and become plot hooks.

trancejeremy: yes, my bad. thanks. got focused on what was and wasn't realistic lunar behavior and managed to completely forget the sun.

 

[SWBaxter]

In a Fictional World that is roughly 25% larger than Earth what would gravity be like?

Just because a thread like this isn't complete without a little math geekiness... it depends what you mean by "larger". The Earth is a little under 13000 km in average diameter, so if the diameter is 25% greater that'd make it around 16250 km. That increases the volume from around 9.2*10^21 m^3 to about 1.8*10^22 m^3, or about double. Assuming density remains the same, mass will also double, and if I've got my math right that means surface gravity is going to be on the order of 1.28G. Other variations on "larger" will produce somewhat different results.

If this world operated by real physical and biological laws, then I'd expect flying creatures to be a lot rarer (magical flying creatures, like Dragons, would presumably be unaffected). Tall plants (i.e. trees) would need to have a much bigger surface imprint to be structurally stable, and probably wouldn't grow as tall. Animals would tend more towards short and stocky. Big animals would mostly be restricted to the oceans, where the water helps to support them. Fewer materials would be buoyant in water (i.e. more materials would sink) - this is because buoyancy depends on weight rather than mass, whatever civilized species you've got would probably be less nautical than on our world; their boats would need to be bigger in order to displace enough water to float. Missile weapons won't travel as far. Undoubtedly many other things change, too, it's all a matter of figuring out what changes, and how.

 

[kigmatzomat]

Ahh. Damn, I was hoping I could just say Hecate revolves around the sun but was close enough to Midgard to act sorta like a Moon. I really wanted one side of Hecate to -never- face the Sun or receive any major light.

Of course I am leaning toward just making it work like the Moon, just have one side constantly facing the sun while the other never does.

That's actually pretty easy. Hecate revolves around Midgard and Midgard revolves around the sun. BUT hecate orbits *very* slowly, making one orbit per year. Hecate's "day" (aka lunar rotation) is also very slow, and one Hecatean day takes one year.

What you end up with is a moon that always puts the same face to the sun. It will probably need to be fairly far away from Midgard and not that massive. (think water/carbon light). But you will never, ever, have an eclipse. Not unless Hecate is *always* in front of the sun. Given hecate's probably small size, this wouldn't hurt midgard (still plenty of light) but would make the sun look like an eye. Planetary rotation would cause the eye to "move" during the day; the Hecate (the pupil) will be looking east (away) in the morning, straight down at noon, and to the west (away) in the evening.

 

[ColonelHardisson]

Ultrazen-

Ahh. Damn, I was hoping I could just say Hecate revolves around the sun but was close enough to Midgard to act sorta like a Moon. I really wanted one side of Hecate to -never- face the Sun or receive any major light.

Actually, both sides of the Moon receive sunlight. There really is no "dark side of the moon." Others can explain it more clearly than I, but we on Earth only see one side of the Moon - including when it's dark, which is what's called a "New Moon" - due to the way the Moon revolves around the Earth.

 

[Nyeshet]

For those interested in odd orbits

Here is another link for you to look at:

http://www.ifmo.ru/butikov/Projects/Collection2.html

It deals with simulations of threebody problems. This particular page presumes an earth, a moon, and a very very small (in mass) third body.

Orbits 1 and 2 are good for an oddly orbitting lesser moon - so too is orbit 5, albeit in an entirely different manner. And orbit 6, although retroactively. These four are the only stable orbits on the page. All others eventually lead to a toss out or (more often) an impact on the moon or the planet (depending on the orbit and the starting conditions).

Orbits 3 and 4 are good for doomsday asteroid. Assuming about 12 'moons' in a year, then the almost 90 degree impact (on the planet or main moon, respectively) take about half a year and dozens of odd orbits around both the planet and the major moon before it occurs.

Orbit 7 would likely end in impact if the simulation lasted long enough. It takes many orbits for the instabilities to show. However, in the description it points out that for the earth/moon system, the triangluar libration point would be stable. Only the extreme mass of the moon in the example (about 50% that of the planet) prevents stability.

Orbits 8, 9, and 10 demonstrate the instability of inner and outter collinear lagrange points. Basically more cases of one or more bodies either being thrown out or pulled in for impact.