This Secret Force Field Is the Reason We’re Alive
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Why does Earth have seasons and how does axial tilt create them?
Winter is coming, said Eddard Stark. When he uttered his famous words in the TV series of Game of Thrones, it was more than just a pronouncement of the normal passing of the seasons. Rather than lasting a mere four months, winter in the fantasy realm of Westeros could be a big problem. It could potentially last for years, even up to a decade. Crops would be harder to grow, the weather would be colder. The arrival of winter was the harbinger of an era of hardship. Of course, while Westeros is pure fantasy, seasons that last for years on end are not limited to fictional stories. We experience them on Earth. Various cycles are playing out on our planet, and when they are in conflict, we experience a period of stability.
It's worth noting though, that they will not be in conflict forever. In our future, winter is coming too. But what are these cycles? How can better understanding them help us prepare for our future? I'm Alex McColgan and you're watching Astrum. Join me today in exploring the different cycles that affect our planet's weather and warmth. To begin, we should probably ask a simple question. What causes the seasons that we are familiar with? You may well already know the answer to this question, but as it will provide the starting point for what comes later, it's worth reviewing. Besides, this question is not entirely straightforward. Depending on where you are on the planet, you may not actually get any seasons.
Generally speaking, seasons we know of are caused as a result of our planet's tilt. Because our planet rotates at a tilted angle as it orbits the Sun, one hemisphere will point towards the Sun during part of the year while the other will point away. Naturally, hemispheres that are pointed towards the sun become much warmer, while pointing away from the sun makes them colder, creating the regular seasons, summer and winter. This effect becomes stronger the higher up or lower down the planet you go. Consider the small Norwegian town of Tromsø. Because of its higher altitude, Tromsø isn't just pointed more towards the sun. The tilt of the Earth is such that from its perspective, the sun never sets for months in summer and never rises for a few months in winter.
Naturally, this produces quite the seasonal variance. but this effect lessens the closer to the equator you get. There, the tilt of the Earth doesn't really change how close or far away from the Sun the area is, and as such, the Earth doesn't notice much temperature variation. It's all just a question of how close you are to the Sun. However, did you know that the tilt of the Earth isn't static? Nor is it the only thing about a planet's orbit that influences how warm or cold we are. Imagine for a second the model you are familiar with, of the Earth orbiting the Sun in a nice circle, flat to the plane of the solar system. In this model, we circle the Sun because of the Sun's gravity. This model is too basic.
In reality, the Sun is not the only source of gravity pulling at us, although it is the biggest. Many of the planets pull and tug at us, particularly large ones like Jupiter, which has a mass 318 times the size of our own planet, or Saturn, which is 95 times, and we in turn pull on them. As planets all rotate at different speeds around the Sun, this constant pulling and releasing creates a delicate dance, far more complicated than a simple circle. This interplay of increasing and lessening gravity has many different effects on our angle of tilt, our orbit, and even the plane in which they occur. Broadly speaking, these variables have stabilised into cycles. These cycles were first described effectively by Serbian geophysicist and astronomer Milutin Milankovic in 1920, and thus were called Milankovic cycles.
The first such cycle I want to look at is the changing shape of our orbit. Over the course of a 100,000 year period, the Earth's orbit around the Sun becomes more and then less elliptical. Naturally, if our orbit is closer to that of a circle, our distance from the Sun remains relatively consistent, and we get about the same amount of sunlight all year round.
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