One of the most significant features of the Game of Thrones universe is the peculiar fact that the both summer and winter can vary in length, and nobody can predict when one ends and the other begins. Though trying to explain this in scientific terms is about as useful as coming up with evolutionary reasons for why dragons or ice zombies should exist, it is nevertheless a fun intellectual exercise. So here are some potential explanations for the irregular seasons in the world of Game of Thrones.

In our world, the seasons are caused by the tilt of the Earth’s axis, so this seems like a good place to start. When the northern hemisphere is tilted towards the Sun, that particular part of the planet gets more exposure to the sunlight, and thus more heat. Then, for the second part of the year, the same is true for the southern hemisphere. The problem is, as you might have noticed, this is a highly regular process, very different from the completely unpredictable cycles in Westeros.

Same problem with a highly elliptical orbit – and besides, the effect from the shape of the planet’s orbit around its star is quite weak. The Earth is almost five millions kilometers closer to the Sun at perihelion (the point in its orbit where it is nearest to the Sun) than at aphelion (the point where it is farthest)… but that happens in early January, so that doesn’t seem to matter all that much.

All these changes in what you could call the dynamics of Earth’s orbit around the Sun can be analyzed together as the Milankovitch cycles. Named after Serbian mathematician and astronomer Milutin Milankovitch, these cycles correspond to variations in our planet’s axial tilt, eccentricity, and precession. Taken separately, the effects on the climate are significant enough, but when they line up, the results can be quite severe. Changes to the amount of solar radiation brought about by Milankovitch cycles might even explain the succession of ice ages in the past million years or so. A similar mechanism could also cause the unpredictable winters in Westeros, though these cycles would have to be a lot quicker than on Earth, where they last from about 23,000 to almost 100,000 years.

Another possible explanation which comes from orbital mechanics is one of the most promising yet: binary star systems. Many of the stars in the Universe have (at least) one stellar companion. They can orbit around their common center of mass, or they can orbit one another – and they can both have planets orbiting around them as well. It’s quite possible that, if the conditions are just right, we could get a system in which a planet orbits one star, and then gets pulled away by the gravitational attraction of the second star – all of this in a very chaotic way which could seem almost random. This very irregular orbit, however, would probably be too extreme for life to thrive.

But the planet could be orbiting either both stars, or just one of them. This would mean than conditions on the surface would be stable enough to at least to support creatures a bit less sturdy than dragons. A group of astronomers has actually published a scientific paper in which they explored a series of explanations for the strange seasonal patterns in Game of Thrones, and according to their calculations, the circumbinary planet hypothesis is the most plausible.

A pretty big problem with this theory is that a second star is something you’d think would be at least mentioned somewhere in the story. Even if the second star is very faint, like a white or brown dwarf or a pulsar, it would still be noticeable. Also, the fact that the big lump of fire in the sky has changed would be a tell-tale sign of the coming of winter. In ancient Egypt, people began to notice the Nile flooded right after a star, Sirius, appeared in the sky. Surely the people of Westeros could have noticed a change to their own sun!

There’s one more potential solution which astronomy gives us: variable stars. Although most stars are relatively stable and predictable when it comes to their energy output, many of them have varying luminosities. Some exhibit this variation in predictable cycles, others seem to be completely random and unpredictable. These cycles can vary wildly, and can last for as much as a few years, which would be consistent with what we know about the duration of seasons in Westeros.

Our Sun itself is a variable star. You’ve probably heard of the 11-year sunspot cycles (which actually last from 9 to 12 years), but the Sun doesn’t seem to care too much about following a schedule. During the second half of the 17th century and early 18th century, very few sunspots were observed. This period, known as the Maunder Minimum, coincided with the coldest part of the so-called Little Ice Age, which lasted from about 1300 to 1850.

Trying to find explanations for stuff in astronomy is always fun, but a planet’s internal dynamics can also cause quick and severe changes in climate. Though the debate is far from settled, atmospheric jet streams and warm waters transported northwards by the Gulf Stream have been named as possible reasons for why winters in western and northern Europe are significantly warmer than those in eastern North America. If, for various reasons, there would be a disruption in the air or water flow, this could also potentially affect the duration and intensity of winter. The Gulf Stream, for instance, could slow down if it mixes with large amount of fresh water (from melting ice or some sizeable body of water finding its way into the ocean). We don’t have a lot of geophysical details about the seas surrounding Westeros, however there doesn’t nothing about this hypothesis which makes it that implausible.

Finally, you know that Little Ice Age I’ve mentioned earlier? According to some scientists, it was triggered by volcanic eruptions – specifically the dust and gas they spewed into the atmosphere. Since the Earth gets almost all of its energy from the Sun, any time our atmosphere gets more opaque to sunlight, the surface of our planet gets colder. Seven hundred years ago, volcanic eruptions might have done precisely that; all the extra ice and snow also reflects sunlight really well, further amplifying the effect. Volcanoes have played a major role in sharp changes in global climate on other occasions as well. The gargantuan 1815 Mount Tambora (Indonesia) eruption, the largest in recorded history, was followed by the so-called Year Without a Summer. An even bigger eruption, which occurred about 70,000 years ago at what is now Lake Toba (also in Indonesia), generated a volcanic winter which might have lasted a decade, possibly reducing the human population to as little as a few thousand people! Once again, while we don’t know of any supervolcanoes near Westeros, one or more in any part of the world, erupting every few years, could explain the erratic change of seasons.

So the reason winter is coming could be related to complex orbital dynamics, variable stars, binary star system mechanics, volcanism, or a disruption in atmospheric or oceanic currents. Of course, we shouldn’t take all these explanations too seriously. We are after all talking about a fantasy series, and George R.R. Martin himself has said the cause for the irregular seasons is magical in nature. But if you’re the kind of person who likes to resort to scientific reasoning as often as possible, you’ll be happy to know astrophysics, geophysics, and meteorology have you covered once again.