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Epic fantasies typically depict northern areas as cold and southern areas as relatively warm. Is this just to play into reader expectations since that's the way it is on Earth, or is there a scientific reason that a planet's northern hemisphere will tend to be cooler?

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    $\begingroup$ What? Surely you mean Equatorial vs Arctic $\endgroup$ – Serban Tanasa May 4 '15 at 19:05
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    $\begingroup$ Earth's Southern Hemisphere is colder than the Northern. $\endgroup$ – Oldcat May 4 '15 at 19:06
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    $\begingroup$ That's not the way it is on earth. Just most of the "deep south" is ocean so we end up with the idea that the south is all hot (plus there's a lot of north hemisphere thinking going on) $\endgroup$ – Richard Tingle May 4 '15 at 19:08
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    $\begingroup$ It's because 90% of the population lives in the northern hemisphere. Most epic fantasies are written by people in the northern hemisphere where south is warmer and north is cooler. $\endgroup$ – wposeyjr May 4 '15 at 19:08
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    $\begingroup$ You could place Antarctica on top and call it the north. We have it in the south now but it has not always been a convention. $\endgroup$ – Vincent May 4 '15 at 20:04
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No, there's no scientific reason to why a given latitude to the south of the average planet should be any different in average temperature to the same latitude north.

Perhaps this is slightly reinforced by the fact that on Earth there happens to be a lower ratio of land to sea in the southern hemisphere than in the northern hemisphere. Antarctica is surrounded by a vast ocean; there's no one living as close to the south pole as, say, northern Russia or Greenland is to the north pole.

Basically, the perception arises because most SF and fantasy writers come from countries in the northern hemisphere, so from their home town things get colder if you go north and hotter if you go south.

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    $\begingroup$ And this carries over to different kinds of "geographical reflexes" so to speak. In Poland we have sea to the north and mountains to the south and if I am to come up with a world for, let's say, an RPG campaign I automatically want to keep it similar. $\endgroup$ – Maurycy May 4 '15 at 20:30
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    $\begingroup$ As well most "planet's" I've seen formed follow Earth's structure pretty close: ie most land mass in northern hemisphere ...vaguely North American shaped contient as the "main" one .. etc. $\endgroup$ – Ditto May 5 '15 at 15:07
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Nope

Most of the Earth's current population lives in the northern hemisphere. That means 88% of people think going north from the current position results in a colder climate.

Why has this translated into fantasy? My only guess is that the authors of those fantasies are simply so used to equating north with cold, that it just carried over. There are exceptions to this, of course.

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Building on the excellent answers others have given concerning the fact that most fantasy has been written from the Northern Hemispherical perspective (and hence via N-S as an increasing temperature axis), there are actually differences between hemispheres which you could build in to your world. You could also make them more extreme.

First, the earth is nearest to the Sun (perihelion) in early January (4th January in 2015). Since the earth is also moving faster around the Sun at that point this means that:

  • the Northern hemisphere gets more solar radiation in its Winter than the Southern gets in its Winter
  • Norther Winters are a little shorter and hence their Summers are a little longer than in the Southern hemisphere

The earth's orbit is very close to being a circle (eccentricity 0.0167) so these effects are not that large. It took a long time before ancient astronomers realised that there was anything going on at all. A more eccentric orbit could make these things rather different.

The date of perihelion also changes (because of the precession of the apsides) very slowly — again, that is something that could be different in an artificial world.

However, another bigger effect means that, counter-intuitively, the earth is actually warmer when it is further from the Sun (at aphelion) because that is when the Southern hemisphere (mostly ocean) gets the Sun's radiation rather than perihelion when the Northern hemisphere gets it. There are two neat explanations of this here:

So you could build a world with a different distribution of continents to change these effects as well.

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    $\begingroup$ And since that isn't complicated enough, ocean currents, like the Gulf Stream can have a significant influence on local climate as well. $\endgroup$ – CodesInChaos May 6 '15 at 9:42
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Earth's southern hemisphere isn't warmer than the northern. The closer you get to the north/south poles, the colder it gets, as those areas get less sunlight than other areas, like the equator. I'm guessing the 'epic fantasy' you're referencing is A Song of Ice and Fire. The weather there is funky and fickle, and no one is certain why it is. There are theories, like the planet this world is on has a wacky axis, or that it isn't even on a planet. You can incorporate some of those ideas into your story.

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    $\begingroup$ Of course if all of westeros is in the northern hemisphere it all makes sense $\endgroup$ – Richard Tingle May 4 '15 at 19:10
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    $\begingroup$ Faerûn or Middle Earth are arguably better examples of an epic fantasy land that fits this description. $\endgroup$ – Samuel May 4 '15 at 19:58
  • $\begingroup$ @Samuel: But Middle Earth explicitly is our own world in a previous age, and though "...the shape of all lands has been changed; but the regions in which Hobbits then lived were doubtless the same as those in which they still linger: the North-West of the Old World, East of the Sea." (From the Prologue to The Fellowship of the Ring.) $\endgroup$ – jamesqf May 5 '15 at 23:25
  • $\begingroup$ @jamesqf I'm not sure if or how your statement agrees with, disagrees with, or adds to my own. Middle-earth, regardless of relation to our Earth, was an epic fantasy land with a cold north and warm south. Right? $\endgroup$ – Samuel May 5 '15 at 23:33
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    $\begingroup$ @jamesqf Our Earth doesn't have a cold north/warm south. It's precisely a northern hemisphere prejudice that leads to the belief. $\endgroup$ – Samuel May 7 '15 at 18:21
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Why do we tend to think of south as hot? This may have something to do with it:

enter image description here

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    $\begingroup$ That graph is wonky. Near the South Pole it should be 100 percent land, not 0. In the North, near the pole should be 0, land, but there's sure more than 12 percent coverage where Siberia and North America ring the Arctic Ocean. $\endgroup$ – Oldcat May 6 '15 at 0:13
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    $\begingroup$ @Oldcat I suspect that this is due to "corrected for circumference", whatever that may be. $\endgroup$ – CodesInChaos May 6 '15 at 9:45
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    $\begingroup$ Ohhhh. You need to explain that graph a lot better, and it needs redrawing, too. It should be a bar graph, not a line graph, because it's not displaying a continuous quantity. (The line is misleading as it makes the viewer think they can read off the value at, say, latitude 6.3 but they can't.) Actually, I don't understand your graph at all. What does "corrected for circumference" mean? What does "contribution of %land vs water per latitude band towards 100% mean"? Towards 100% of what? If it's a contribution towards 100%, then shouldn't all the datapoints of each colour add up to 100? etc. $\endgroup$ – David Richerby May 7 '15 at 7:17
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    $\begingroup$ Right now, I'm not convinced that the quantity you're graphing has any actual meaning. $\endgroup$ – David Richerby May 7 '15 at 7:18
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    $\begingroup$ Major edit; replacing the graph. $\endgroup$ – user9394 May 7 '15 at 15:16
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The solar exposure difference between the northern and southern hemisphere is determined by the planet's spin axis and the planets equator (perpendicular to the spin axis), as in this picture:

Equator

So you could potentially have a gravitationally locked planet (like Mercury) with a spin axis of -90' (like Uranus) and its northern hemisphere exposed to the system's star all year long and scorched, and the southern hemisphere plunged in the dark and blistering cold, with the only life possible being in a ring 5 degrees below the equator in the southern hemisphere. In reality such a planet would probably not be habitable because of insane weather and thermal stress constantly cracking the surface due to the enormous temperature delta between both hemispheres.

I think it's just easier to say north is colder than south from a northern hemisphere point of view, almost metaphorically, especially in science fiction.

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  • $\begingroup$ There are some really important details missing here (e.g. how do you get "the northern hemisphere exposed to the system's star all year long") which lead you to make statements that are exactly backwards ("tidal forces constantly cracking the surface"). $\endgroup$ – Rex Kerr May 6 '15 at 20:07
  • $\begingroup$ Also let's not forget this isn't Astronomy, the question was asked from a fiction point of view. I would like to hear what makes you think my statements are backwards and my details "missing". If you will downvote an answer, I would at least expect you to provide a better one. Uranus has in fact an axis tilt of 97 degrees, so you don't have to look far for examples. $\endgroup$ – Drunken Code Monkey May 6 '15 at 20:40
  • $\begingroup$ Tidal forces are constant when you're either gravitationally locked or have a pole facing what you're orbiting. (You can't have both due to conservation of rotational momentum.) So in the scenario you state, tidal forces would be mild (due to orbital eccentricity). But the scenario is not physically possible, as far as I can tell from the details you've given. $\endgroup$ – Rex Kerr May 6 '15 at 21:47
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For conventional planets it's completely wrong that the southern hemisphere "is colder".

When you are in one hemisphere or the other,

it gets warmer as you move towards the equator.

So, IF you are in the Northern hemisphere, it gets warmer as you move South.

So, IF you are in the Southern hemisphere, it gets warmer as you move North.

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    $\begingroup$ "when you are in one hemisphere or the other, it gets colder as you move towards the equator." So Morocco is colder than Finland? Good to know. I think you meant to write that it gets warmer as you move toward the equator (but I'm not going to unilaterally make such an edit to an answer that already has upvotes). Which of course doesn't necessarily work either; compare Uranus for an extreme example of what a whacky axial tilt can do. The reason why the Uranian equator is less cold than the poles is unknown. $\endgroup$ – a CVn May 5 '15 at 8:59
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    $\begingroup$ As Michael says. The claims here are wrong and you have received down votes for that; correct the mistakes and they may be retracted. $\endgroup$ – ArtOfCode May 5 '15 at 13:05
  • $\begingroup$ No, it doesn't, to be brutally honest. The science here is still wrong and I don't what any typo has to do with it. $\endgroup$ – ArtOfCode May 21 '15 at 0:39
  • $\begingroup$ You raise a very good point with some social implications (so I'm not surprised your answer was downvoted;) Beyond the social implications, I suspect part of the reason is that there is more real estate in the colder parts of the Northern hemisphere than the Southern. $\endgroup$ – DukeZhou Jul 20 '17 at 16:48

protected by ArtOfCode May 10 '15 at 23:10

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