# Hemisphere problems!



## deilaitha (May 23, 2012)

In the novel I am currently writing, the premise hinges on the concept of two parallel universes.  The characters manifest differently in each universe--not necessarily opposite, but differently.  

As I was plodding/plotting along, one of my characters was trying to orient himself and he mentioned that he did not think they were in a Northern mountain range because it was not cold.  That was when I realized that fantasy writers frequently, if not exclusively, write from a Northern-hemisphere perspective.  I suppose it may have to do with the fact that high fantasy in particular has its origins in Europe.  So, just to twist things up and to emphasize the difference between the universes, I changed the perspective: in one, the further south one goes, the colder it gets; in the other, the further north one goes the colder it becomes.  

So now here's the question:

I've never been in the Southern Hemisphere!  Does it get colder the further south you get?  I know our summer is their winter and vice-versa, but is the weather like a mirror image of the Northern Hemisphere?  Geography and science were longer ago than I care to admit.  

Also, I was going to have it be summer in both universes simultaneously (they currently are running at the same time-speed), but I was now contemplating the significance of that in light of the new hemisphere concept.  If they are on the same time schedule, would Universe 1's summer be Universe 2's winter?  I do want to avoid the idea that the Universes are opposites of each other, but this hemisphere concept has intriguing implications. 

And then there is the whole problem of flat vs. round world...so many things I have not thought about. 

Any helpful suggestions or comments?


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## Steerpike (May 23, 2012)

Yes, as you go further south from the equator, it will tend to get colder, just as when you go further north from the equator, though I don't know that the temperature distribution is the same given unequal distributions of land mass, how ocean currents come into play etc. But as a general rule, yes it will get colder as you move south. Antarctica is covered with ice for the most part.

Based on how you describe the two universes, then it does seem like summer in one would be winter in the other (in that same hemisphere).


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## Caged Maiden (May 23, 2012)

Yeah, what Steerpike said.  However, I live in Albuquerque, and I'd call that a southern mountain range, but it's darn cold here.  In fact we get snow in May and September here frequently, but are technically a desert.  If they're in the mountains anywhere, it's probably going to be cold (and windy and hot because of the thin air, unless they're low-lying mountains).


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## Ravana (May 24, 2012)

Yup, as mentioned, it's primarily distance from the equator which does it… on Earth. Ah, but there's the catch.…

This will still be true on _most_ planets, because most planets will have an axis of rotation that isn't too far from being perpendicular to the plane of their orbit, aka the ecliptic. (This is a consequence of how they are formed in the first place.) The less the axial tilt, the closer the equator is to the orbital plane. Earth's axis is angled at about 23.5Âº from perpendicular, and this tilt is the reason we have summer and winter: if it were directly perpendicular (a tilt of 0Âº), we wouldn't have these seasons—possibly, wouldn't have "seasons" of any sort. The northern summer occurs when the North Pole is angled toward the sun and the South Pole away from it, vice versa for winter.

The Southern Hemisphere on Earth has, for the most part, milder temperatures during its winter, but this is because most of the land in the Southern Hemisphere is closer to the equator: apart from Antarctica, all but a tiny bit of South America and New Zealand is above 45Âº south latitude… whereas the 45Âº north latitude line crosses southern Europe, runs north of Turkey, south of nearly all of Russia, and comes back around just south of most of the U.S./Canada border. As a consequence, there are a lot more people living in a lot more places far from the equator in the north than in the south, and so a lot more of them are exposed to harsher winter conditions. Also, the mere fact of there being so much more land in the north affects the climate, since ocean currents transport considerable warmth to nearby land in many parts of the world; the farther away from the oceans you get, the less effect this can deliver. Which is why Siberia is such a lousy place to live: not only is it well into the northern latitudes, but most of it is thousands of miles from any warm ocean. By comparison, even the more southerly reaches of the southern land masses are fairly close to warming currents: South Africa almost never sees snow, while South America, Australia and New Zealand only see it in the mountains, and few of these are snow-capped year-round (none in Australia are, as far as I know), at least until you get all the way down to the deceptively-named Tierra del Fuego at the southern tip of South America, which is about as far south as central Canada is north… and even it receives the benefit of warming currents, whereas most of Canada does not. 

Antarctica, of course, is almost completely capped in ice—a mile or more deep—even in southern summer. So, yeah, if you go far enough south, it'll get cold again. 

However… planets don't _have_ to have a tilt close to perpendicular to the orbital plane. Uranus has an axis that is almost straight-on to the ecliptic. Actually, it's tilted slightly past the ecliptic—97Âº—so that what little rotation it does have relative to the ecliptic is in the opposite direction of the rotation of the other planets in the solar system… except for Venus, which is tilted at 177Âº, which means its axis is almost perpendicular to the ecliptic but its rotation is in the opposite direction from what is expected. Direction of rotation won't matter in terms of determining seasons, however, only the tilt; thus Venus would have almost no seasonal difference between north and south. Uranus, on the other hand, would have _extreme_ differences—since at one part of its orbit, the _entire_ northern hemisphere would be receiving sunlight, and _none_ of the southern hemisphere would, while at the opposite end of its orbit, the situations would be reversed; halfway between these two points, the entire planet would be receiving sunlight in equal amounts, as its equator would be lined up with the sun.

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As for whether or not your parallel-universe planets have the same seasons at the same time, that's entirely up to you. If you want to make them perfectly parallel, they'd have the same seasons… but, let's face it, it wouldn't be too unreasonable for one of them to have "slipped" six months—or any other differential you wanted to impose—behind or ahead of the other over the course of 4.5 billion years. [I have a hard time buying into "parallel" universes in the first place, as happens, but that's just me.]

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Flat worlds are another story altogether. Since they are essentially impossible from an astrophysical standpoint—that is, they can never form naturally—worrying about what happens in the real world won't matter a whole lot. If one were to be created artificially (through engineering, magic or divine intervention), it would, presumably, be given a perpendicular axis… and at least in the case of being built by super-science engineering, it would probably be given a rotational period ("day") equal to its orbital period (year), so that one side always faced the star it was orbiting. At least I can't see much advantage of it being set spinning so that both sides received equal light, given some of the other problems that would be created by having a flat world: it would be better (and a lot easier) to build a normal, spherical one if that's what you wanted.


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## deilaitha (May 24, 2012)

I suppose I did not think overly much regarding that altitude affects temperature as well.   Thanks for pointing that out.


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## SeverinR (May 24, 2012)

I believe the seasons are opposite in the southern hemi.

Cold during our summer, and warm during our winter. Because of the axis, when we are in summer they are tilted the other way.

I had not realized that there was less land to the south then the north, but when I picture south America, its more tropical and less wintery. Same with Australia. I just figured the wintery parts weren't as popular, because it was so less populated.


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