Irregular Seasons: Explain to a Non-Science Person

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.

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, 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.

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.)

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."

Maryn said:

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?

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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.

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.

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?

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.

dempsey said:

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.

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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 (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.

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[sup]*[/sup]), 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.

[sup]*[/sup]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"

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.

WriteKnight said:

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.

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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.

Pthom said:

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.

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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.

WriteKnight said:

Again, the definition of 'year' is never made clear.

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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.

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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.

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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.

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.

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?

SPMiller said:

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.

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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.

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.

Bartholomew said:

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.

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And likely a place where life is unlikely, if not impossible.

Pthom said:

And likely a place where life is unlikely, if not impossible.

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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

In a complex planetary system, your planet could be orbiting in a strange 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.

Maryn said:

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

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Just one?