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View Full Version : Irregular Seasons: Explain to a Non-Science Person



Maryn
07-20-2008, 08:33 PM
I'm halfway through a reread of a massive fantasy series in which "Winter is coming" is an oft-repeated reminder that he who is not well prepared will not survive.

(It's the excellent "Song of Ice and Fire" series by George R.R. Martin, beginning with A Game of Thrones. I'm not a fantasy reader, so I resisted the prods and pokes for some time, but once I started it, I was hooked.)

The characters make many references to winters lasting nine years, or only three, or twenty-five, or to unusual springs that went on for years and years, etc. How might this be possible?

I know what makes earth seasons, the tilted axis and our roughly circular orbit around the sun. (Boy, fourth grade was great, huh?) I can't imagine a set-up which allows for irregular lengths of seasons. Martin has been so meticulous about his other research that I doubt he gave it no thought.

An orbit that isn't circular seems necessary, but a plain parabola won't work, I don't think. There's only one sun, BTW.

Any math-and-science people want to take a stab?

Maryn, adorably befuddled (well, befuddled anyway)

alleycat
07-20-2008, 08:41 PM
Another possibilities might be a planet where the axis tilt varies due to some sort of shift in its core. I've never given it much thought; well, actually I haven't given it any thought until now.

A non concentric orbit seems like an easier explanation however. The planet would then sometimes be closer to the sun than at other times. Just a slight bit out of concentric would make a lot of difference I think.

WriteKnight
07-20-2008, 09:05 PM
Well, a 'year' is never defined in the book - though we certainly assume its the same as an earth year.

I gave that some thought while I was reading the series. It's never explained but I assumed an eccentric orbit, an eccentric 'wobble' of the tilt... (So its possible the northern hemisphere could be in winter for greater or lesser points on an eccentric orbit) -and some sort of climactic global cooling/heating that is not mentioned.

Funny aside - the pic of me in my Avatar - I was riding through a faire in a snowstorm, and people kept calling out "Eddard Stark!" - I didn't know who he was, as I hadn't read the book.

Maryn
07-20-2008, 10:19 PM
SPOILERS AHEAD

Luckily, you seem to have retained your head. So far.

Maryn, who very much liked the startle that came with the unexpected death of a good guy character

SPMiller
07-20-2008, 10:30 PM
Maryn, if you liked that, you're going to love the rest of the books...

While orbit and axial tilt are no doubt factors, what I want to know is how anyone manages to survive a decades-long winter. I can't think of much food that will keep that long without spoiling. In fact, almost everything would be dead by the end of it, flora and fauna alike. Maybe some seeds and species of trees could adapt to go dormant for that long, but not much else. Recovery would take a while.

FennelGiraffe
07-21-2008, 04:02 AM
The only configuration I can think of that would give seasons that irregular would be a binary system, with the planet in orbit around only one of the stars. For a very rough approximation, imagine our solar system with Jupiter about 20 times more massive. That would make it a very small star, and we would probably feel some heat from it at closest approach (when Earth and Jupiter are lined up on the same side of the Sun). In reality, making Jupiter 20 times larger would cause a bunch of other effects, but this should give an idea of the geometry of the situation.

Because Earth and Jupiter have different orbital periods, that closest approach occurs at different times of the Earth year. In a particular year when closest approach occurs during summer in the Northern Hemisphere, then the Northern Hemisphere would have a super-summer that is hotter than usual. Even though the season in an astronomical sense remains the same length, the hot weather would last longer and be perceived as a "long" summer. That same year, the Southern Hemisphere would have an unusually mild winter that would be perceived as shorter than normal.

Ooohh, it gets even better if the planet orbits the smaller star (a little smaller than our Sun), which in turn has an elliptical orbit around a much larger, hotter star. There would be a significant variation in the amount of heat received from the large star, and that would be on a very long cycle. (I haven't run specific numbers, but at least twenty Earth Years, probably more than a hundred.) The planet would also have a normal year with regard to its orbit around the small star. To visualize this, put a giant star where our Sun is, our Sun where Jupiter is, and Earth where one of Jupiter's moons is. Then expand the scale quite a lot so everything is much farther apart.

If the small star isn't quite hot enough, you could get some pretty severe winters when the small star is at the far point of its orbit around the large star. On the other hand, when the two stars are at closest approach, there would be summers where the planet is between them and never gets dark. That would be intensely hot.

It is a characteristic of elliptical orbits that the time of closest approach is when they move the fastest, so they are close together for only a small fraction of the total orbital period. The more elliptical the orbit is, the more pronounced this effect is. (Kepler's second law--the equal areas in equal time bit.)

Pthom
07-21-2008, 05:26 AM
Another possibility is that the planet's star is variable. It is sometimes on, sometimes not. For a fictional treatment of such a scenario, read Vinge's "A Deepness in the Sky."

Prozyan
07-21-2008, 06:17 AM
The characters make many references to winters lasting nine years, or only three, or twenty-five, or to unusual springs that went on for years and years, etc. How might this be possible?

GRRM has said previously that the long winters/summers are the result of the balance of power and the struggle between "The Others" and, well, the others.

WriteKnight
07-21-2008, 06:33 AM
Ah, its a 'magic' thing then. That's cool. I didn't worry too much about the mechanics, I took it as a given.

Maryn - NO ONE is sacred in these books. No. One.


My son says they've started production on the mini-series? Way cool.

MattW
07-21-2008, 07:23 AM
IIRC, GRRM may have said that there is some logic behind the seasonal variability in addition to the "magic" explanation.

The way I see it, the increase in magic is also coincidental with the appearance of a comet, all at the same time as a Winter like they haven't seen before.

This unpredictability in timing, duration, and severity of the season makes me think there is a partial astronomical cause. The planet may be passing through a cloud of interstellar (or dark) material that absorbs a portion of solar radiation, signaled by the density of comets. Or perhaps the comets themselves offer an explanation of another celestial body with overlapping orbit or gravitational field that affects the rotation of the planet. Or, the sun of the system resides very close to a galactic core and is actually spiraling into a massive black hole, the result of which is all sorts of gravitational oddities and interstellar debris fields.

Of course, this also assumes that any of those things also influences the prevalence of magic and the viability of dragons as a species. So, really, how much can we deduce about the seasonal changes?

geardrops
07-21-2008, 09:02 AM
A potential reason--and astronomers, correct me if I'm wrong--is that the world's sun isn't the orbital point, but that the sun and the planet share some sort of focus they both orbit around, making the winters vary.

No, it's not what GRRM said. It's just something I thought up that might work out. But I'm a lowly programmer and ill-knowledged in the motions of heavenly bodies.

FennelGiraffe
07-21-2008, 06:11 PM
A potential reason--and astronomers, correct me if I'm wrong--is that the world's sun isn't the orbital point, but that the sun and the planet share some sort of focus they both orbit around, making the winters vary.

That's true of all orbits. A planet doesn't orbit a sun; the planet and sun both orbit their mutual center of mass. A moon doesn't orbit a planet; they both orbit their center of mass. And so on for any two bodies.

When there is a substantial size difference between the two bodies, the center of mass is inside the larger body. Slightly less difference and the center of mass is very close to the larger body. In those cases, the larger body just wobbles a bit, and the smaller body looks like it's orbiting the larger one. When the two bodies have close to the same mass, on the other hand, this becomes a significant distinction.

There are some animations here (http://en.wikipedia.org/wiki/Center_of_mass) (scroll down).

(I'm no astronomer. But I grok orbital mechanics.)

I haven't read the series in question, but if GRRM gives a handwavey explanation, and makes it work, that's fine. Even though I enjoy looking for the scientific justification, when a story is well-written that's something I don't think about until after I've finished reading it.

Pthom
07-21-2008, 09:27 PM
I can't imagine a situation in any orbital system where a planet could orbit a star (or stars) so irregularly as to cause random seasons. Orbits are periodic. If you have a planet that experiences a 25-decade-long winter (a definitional improbability, that*), then it will do so on a regular basis. Extreme elliptical orbits (such as those of comets) can result in very long and very cold "winters" and very brief and very hot "summers". There is no such thing as a parabolic orbit as far as I'm aware. A parabola is an open-ended curve. An astronomical body following a parabolic trajectory comes, stays briefly, and departs. However, if the object at the focus of the parabola is massive enough, then the parabolic trajectory may become an ellipse--or ultimately a circle--yet the orbiting object still revolves in a regular, periodic manner.

An orbital configuration so anomolous as to allow such random-length "seasons" is likely to cause the planet to crash into one or the other of the stars, or be ejected from the system, or some other catastrophe, and that would happen sooner than later, making it highly unlikely that life could develop (or sustain) there.

*A decade as used here means ten years. A year is defined as one revolution of a planet about its star. To have 250 years of winter, then, the fire of the star would have to "go out" for that time.

um--it just occurs to me that if a large enough body were to orbit the star inside the planet in question's orbit and if the orbital velocity of that large body was just right and if its presense in the solar system didn't disrupt anything else (unlikely) then if it were to pass between the star and the planet once a long while, blocking solar radiation from reaching the planet...

But that's a lot of "ifs"

WriteKnight
07-21-2008, 09:34 PM
Again, the definition of 'year' is never made clear. But if you look at the earth's history in terms of Ice ages, and such - then there have been 'long winters' on earth.

Like I said, a bit of magic here, a bit of orbital mechanics there, a bit of enviromental voodoo overall - you could make it feasable.

Pthom
07-21-2008, 11:54 PM
Again, the definition of 'year' is never made clear. But if you look at the earth's history in terms of Ice ages, and such - then there have been 'long winters' on earth.

Like I said, a bit of magic here, a bit of orbital mechanics there, a bit of enviromental voodoo overall - you could make it feasable.In a fictional setting, of course. In fiction, just about anything you like is possible.

However, this is the science fact sub-forum, and we do try, here, to keep things as close to known scientific fact as possible. :)

FennelGiraffe
07-22-2008, 03:50 AM
I can't imagine a situation in any orbital system where a planet could orbit a star (or stars) so irregularly as to cause random seasons.

Depends on how you define "irregular". Random: no. Variable: yes. If the longest cycle takes more than a few lifetimes to complete, it would need a well-established civilization to have records going back far enough to make the pattern apparent. Until the pattern is worked out, it could look pretty darned irregular to the natives.

Also depends how much detail the story goes into. If the story isn't too specific, just mentioning long and short winters in passing, without explaining exactly when they occur, it could sound seriously irregular.

Prozyan
07-22-2008, 04:11 AM
Again, the definition of 'year' is never made clear.

Its true that it is never directly stated how long a "year" is within the ASOIF universe, but there is strong anecdotal evidence that it is at least very close to the standard Earth year. The age of the children, age of parents, length of the Targaryean rule and the number of generations involved. It all pretty much points to something extremely close to an Earth year.



A planet doesn't orbit a sun; the planet and sun both orbit their mutual center of mass.


Very true, this principle was the first technique used to detect extrasolar planets. Scientists looked for "star wobble".



GRRM may have said that there is some logic behind the seasonal variability in addition to the "magic" explanation.


As far as I know, he has only put forth a "magical" explanation for the seasons being "out of balance" as GRRM puts it. Aside from that, the only possible explanation I can think of is an extremely long orbital period.

SPMiller
07-22-2008, 04:13 AM
GRRM's ASoIaF world contains many societies sufficiently well-developed and established to keep records. There are examples of ridiculously detailed, long-term records in the books. The book of the Kingsguard, for instance, and the histories of the Night's Watch. They go back for centuries, if not millennia. Surely someone would've looked at the books at some point and realized the pattern.

small axe
07-25-2008, 04:32 AM
Does it have to be related to your world's orbit though? (forgive me if I missed some detail above)

What if they're just worrying about some periodic "little ice age" (caused by ... um ... whatever causes our own Ice Ages)?

There was a TV episode (?) about Europe's "little Ice Age" of the Middle Ages, or "the year with no summer" in 1770's ... due I suppose to irregular Sun output (suggested above) or volcanic eruptions that put enough dust in the atmosphere to reduce sunlight/sun heat, or fluctuations in your planet's magnetic field, or ... similar (perhaps predictable, on a world where the pattern is more obvious) non-orbit causes?

Anyway ... maybe that could work too?

MattW
07-25-2008, 09:04 PM
GRRM's ASoIaF world contains many societies sufficiently well-developed and established to keep records. There are examples of ridiculously detailed, long-term records in the books. The book of the Kingsguard, for instance, and the histories of the Night's Watch. They go back for centuries, if not millennia. Surely someone would've looked at the books at some point and realized the pattern.
The Maesters of Oldtown send out messages when they have determined that Winter is about to begin. They must also have some way of knowing the pattern (if there is one), or observing the telltale signs of imminent change in season.

We haven't seen enough, but they are obviously skilled (or at least knowledgeable) in astronomy, astrology, and magic.

Bartholomew
07-29-2008, 01:46 PM
The non-concentric orbit is the best explanation I've heard, so far. Couple this with an irregular, or perhaps complicated "spin" on the planet itself, and you've got some truly wonky weather incoming.

Pthom
07-30-2008, 01:19 PM
The non-concentric orbit is the best explanation I've heard, so far. Couple this with an irregular, or perhaps complicated "spin" on the planet itself, and you've got some truly wonky weather incoming.
And likely a place where life is unlikely, if not impossible. ;)

Bartholomew
07-30-2008, 02:06 PM
And likely a place where life is unlikely, if not impossible. ;)

The difference of a few miles would be enough to cause bitter cold or extreme heat. We don't need to fling the planet into deep space. o-o

Priene
07-30-2008, 02:30 PM
In a complex planetary system, your planet could be orbiting in a strange attractor (http://en.wikipedia.org/wiki/Attractor). Rather than travelling in a straight orbit, its distance and/or inclination could vary chaotically within certain parameters. So it would be impossible to predict how far from the sun the planet would be in ten years time, say, but it would be possible to say that it would be within an minimum and maximum distances. Winter could last for nine years, then four years summer, two years winter, six years summer, whatever you like.

dmytryp
07-30-2008, 06:23 PM
SPOILERS AHEAD

Luckily, you seem to have retained your head. So far.

Maryn, who very much liked the startle that came with the unexpected death of a good guy character

Just one?

Sarpedon
07-30-2008, 06:43 PM
Umm, no, the difference of a few miles would not make any difference in climate. The earth's elliptical orbit means that our distance from the sun varies by about 5 million kilometers. In fact, we are closest to the sun during the Northern hemisphere's winter. It is the angle of the earth's axis, not the distance to the sun, that is the big factor.

Radiation follows the Inverse Square Law; one of the most important laws of physics, meaning that if you increase the distance between a radiation source and its target, the amount of energy that reaches the target is reduced by a factor that is the square of the original change.

So, since the earth orbits at a distance of 150 million km (on average) from the sun, the difference of 2.5 million km from the average is about .016. If you square that, you get...a very small difference in the amount of energy reaching the earth. Needless to say, a difference of a few miles either way wouldn't be noticeable.

Sadly, the idea that such a small difference would wipe out all life on earth is a myth that is spread by Intelligent Design advocates, in order to further their idea that life couldn't possibly have come about naturally. In reality, there is a range of several tens of millions of miles that the earth's orbit could be in without rendering the planet inhospitable to life

http://en.wikipedia.org/wiki/Earth%27s_orbit

Bartholomew
09-09-2008, 05:05 AM
Cool. :)

Maryn
09-09-2008, 05:20 AM
Bart, are you familiar with the series? My son's about your age (how did I get so freakin' old, again?), and he's read and reread them, even though he's not really a fantasy guy. I'm not a fantasy person either, but I enjoy this one series a lot.

Maryn, midway through the fourth book for the second time

Bartholomew
09-09-2008, 09:42 AM
I'm familiar with it in passing. I've got them on my list.

The one that I could use to insulate my apartment.

lpetrich
10-19-2008, 08:29 PM
(It's the excellent "Song of Ice and Fire" series by George R.R. Martin, beginning with A Game of Thrones. I'm not a fantasy reader, so I resisted the prods and pokes for some time, but once I started it, I was hooked.)

The characters make many references to winters lasting nine years, or only three, or twenty-five, or to unusual springs that went on for years and years, etc. How might this be possible?
I'll take a stab at it. I'm fairly familiar with the relevant physics, so here goes.

First the astronomical possibilities. Such a climate could happen if a planet orbits amidst a binary star -- it would have a very irregular orbit.

In fact, astronomers have done lots of simulations of possible binary-star planets to find out which planet orbits are likely to be stable, and they find that such an orbit will likely be unstable -- the planet is likely to be ejected by a close encounter with one of the stars.

I've crunched the numbers myself with the help of an orbit simulator, and I've found that that often happens.

But there are orbits of planets in binary-star systems that are stable, at least within the limits of the simulations.

In a satellite-type or S-type orbit, a planet orbits one of the stars. Its distance from the stars must be less than about 1/3 times the stars' separation for its orbit to be stable.

In a planetary-type or P-type orbit, a planet orbits both of the stars. Its distance from the stars must be more than about 3 times the stars' separation for its orbit to be stable.

Planets in these orbits will be perturbed either by the other star (S-type) or by the stars being separate (P-type), so the orbits will precess and have various wobbles. These, however, will essentially be regular and periodic, and will not be able to cause those irregular climate oddities.

fullbookjacket
10-19-2008, 08:58 PM
I haven't read through all the posts in this thread, so I don't know if someone has offered these explanations.

You might explain the variable seasons by means of a "wobble" in the planet's orbit. Earth has a slight wobble in its orbit, on the order of tens of thousands of years apart. The wobble affects long-term climate, such as recurrent ice ages.

You might also go with a plate tectonics approach. Maybe every few decades, a planet's plates become more active, resulting in greater volcanic activity, resulting in greater suspended dust, resulting in global cooling.

Either of these might work hand-in-hand with interruptions of warm ocean currents. Theoretically, global warming can result in the ironic result of global cooling. If Earth's Arctic ice continues to melt, it releases fresh water into the salty North Atlantic. The band of fresh water is currently shown to be advancing south. What this could do is shut down the Atlantic conveyor, which brings warm water up from the tropics and warms the climate of North America and Europe. This is the theory rather weakly explained in the movie "The Day After Tomorrow".

fullbookjacket
10-19-2008, 09:04 PM
Here's another idea.

On Earth we have long-term patterns (20-30 year cycles), called El Nino and La Nina. They affect mildness or severity of winters. Very simple explanation.

Also, another way in which global warming could trigger an ice age is through the amount of humidity. Currently, the Arctic is frozen ice, but very dry. There's not much snowfall at all in the Arctic because the air is so dry. As the climate warms, so does the likelihood of increasing humidity in the Arctic, and therefore more snow. If snowfall increases, you'll get more of it piling up each year, resulting in glaciers. Voila! A new ice age!

lpetrich
11-09-2008, 12:01 PM
What causes the El Niņo Southern Oscillation (http://en.wikipedia.org/wiki/ENSO) continues to be obscure; it may be some sort of oscillation in the ocean, where the top layers get heated and then spread out.

Normal: most of the equatorial Pacific Ocean is warm, while cold water upwells at the South American coast. This is good for fishing because the water has greater oxygen capacity and more nutrients.

El Niņo ("The Boy"): the warm water spreads to the South American coast. Not as good for fishing, because of warm, nutrient-poor water. It got its name from when it often occurs, Christmas, the celebration of the Christ Child.

La Niņa ("The Girl"): there is more cold water upwelling near the South American coast than usual. Its name is from it being the opposite of El Niņo.

El Niņo and La Niņa have several climate effects, mainly in tropical and subtropical areas, but some further away from the Equator.

It is rather difficult to do long-range predictions of the ENSO, it must be said; its variations are rather chaotic and at best semiregular.


Another interesting semiregular effect is the formation and draining of glacial lakes. Glacial-lake outburst floods (http://en.wikipedia.org/wiki/Glacial_lake_outburst_flood) happen with some present-day glaciers, but there were some big ones that happened during the last Ice Age. Notably the Missoula floods (http://en.wikipedia.org/wiki/Missoula_Floods) of 15,000 - 13,000 years ago. The North American glaciers reached the peak of their extent back then, and one bit of glacier dammed the Clark Fork River, near Missoula, Montana. This produced a lake that would fill up for about 55 years, then break through the glacier, causing a giant flood that poured down the Columbia River basin. A flood that could flow as fast as 80 mph / 130 kph, that produced giant ripple features in the landscape, and that carried boulders with it.


So there could be something like the ENSO or big bursting glacial lakes that causes big climate hiccups.

MelancholyMan
11-18-2008, 07:40 PM
Perhaps your planet is orbiting a fast moving star that is currently transiting a spiral arm. It would encounter regions of dust that while too thin to see, would obscure the suns rays enough to cause changes in climate. Totally irregular and impossible to predict.