Wednesday, August 31, 2011

Stumped by the Seasons in Game of Thrones

There will be no simple explanation for the unusual seasons of George R.R. Martin’s addictive Game of Thrones (other than: it’s a fantasy.) Bummer.

(Second book in the series. Not as awesome as the first, but still compulsively readable.)

In these books, “summers can last for years and winters a lifetime”. How?

Let’s start with our planet. You know the earth has a tilt, right? Summer in the northern hemisphere occurs when the sun’s rays hit the north more directly and the days are longer. Six months later earth has moved to the other side of the sun. Now the sun's rays hit the north on a more extreme angle, the days are shorter, and we have winter. Here’s a nifty graphic from Zoom Astronomy:

The earth zips around the sun in 365 days and so this pattern repeats every year. Fab.

Could we create years-long seasons by adjusting the tilt of the earth? A changing axial tilt is not out of the question. According to Wikipedia, the earth’s tilt or obliquity varies from 22° 38’ to 24° 21’. On other planets the variation is more extreme. Mar’s obliquity may vary “between 11° and 49° as a result of gravitational perturbations from other planets.

Yet there are problems with simply increasing the tilt to make the winter more harsh. The variation I mention above for earth’s tilt happens every 41 thousand years. In our fantasy world, we need the axis tilt to change from say 23° (summer years) to 25° (winter years) within a couple of years. Second, the position of earth’s tilted axis stays constant as the earth orbits the sun. If we look at the axis over the course of a year, we get a slice of penne pasta:

Yummy. So if you increase the tilt to create an extreme winter for the north, it would be followed by a sizzling hot summer six months later. What we really need is an axis that keeps the northern hemisphere tilted away from the sun’s direct rays all year long. Then the axis rotated around the sun would form a bowl (leaving the southern hemisphere with a long, long summer.) Bowl, pasta. I need lunch.

I’m not astronomer, so I can’t tell you if this is possible. Perhaps some “gravitational perturbations” from nearby planets could help. This is a fantasy world, so you could play with the solar system. Plus, the moon could become a factor by increasing its size and/or its distance from fantasy earth. But here’s the kicker. Our fantasy seasons are not cyclic. Summers are shorter (5 to 15 years) and winters longer (15 to 50 years). So putting the explanation on planetary movements (which are cyclic) is tricky.

(If you really want to stretch you brain, read about Milankovitch cycles. Besides axial tilt, eccentricity and precession of the earth’s orbit can affect climatic pattern. To contract your brain, go read up on Mila Kunis.)

So if I continue this quest, I’d study the onset of ice ages and maybe El Niño/La Niña events. But I really need to get (a life) back to writing and lock my (inner nerd in a closet) energies onto worlds of my creation.

What's distracting you these days?


  1. This was interesting to read. I used to love that portion of science as a child--earth tilting, seasons, and whatnot.

    I'd like to read this series someday.

    Have a great weekend.


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