IN THIS SERIES, TheJournal.ie takes a look at an urban myth, old wives’ tale, or something that your mammy told you years ago to see if there’s any truth in it.
Seasons, as you have probably noticed, are an incredibly important aspect for all our lives.
It allows us to say that there’s “a great stretch in the evenings” in spring and “you know I put the heating on the for the first time tonight” at some point in Autumn.
However, in classrooms across the world, children are taught that the Earth’s distance from the Sun is what causes them.
Unless they have some interest in astronomy, most people won’t think twice about it as the science behind the claim seems black and white. The Earth’s orbit around our star isn’t a perfect circle, and at points we are closer to the sun than at other times. The closer we are, the warmer our weather will be, and the further away we are, the colder it gets.
Earth warmer when further away
This distance actually has very little to do with our planet’s seasons. In fact, the Earth is warmer when at its furthest point away from the Sun.
What should be a simple straightforward fact taught in primary school Geography class has become a misunderstanding so widespread that studies have been conducted into how prevalent it is, and how inaccurate some teachers are with the basic elements of astronomy. One even found that Harvard graduates were still getting it wrong.
What actually causes seasons is that our planet is tilted over by 23.5 degrees, known as its “axial tilt”. As we spin around the sun, at different points of the year the North Pole is either tilting towards or away from the sun, although never directly at it.
This is not the planet rocking back and forth, the tilt is fixed, as seen in the diagram below.
Click here to view a larger version of this image. Global on the left shows summer in the Southern Hemisphere, on the right, summer in the North (Image Credit: Wikimedia Commons)
This means that depending on the time of year, either the Northern or Southern Hemisphere is more exposed to the sun, which means longer days, more sunlight from directly overhead, and so more time for the Earth is absorb heat. The result: A summer.
At the same time, the other side is leaning away, has shorter days which means less heat is absorbed. The sun isn’t as directly overhead, and so its rays are not as strong and warm. The result: A winter.
Click here to view a larger version of this image. The four main points of Earth’s axial tilt (Image Credit: Wikimedia Common)
That’s why when we are rejoicing at yet another beautiful Irish summer where temperatures soar, Australians experience their winter.
It’s also what gives us the shortest day of the year and the longest day of the year, known as the summer solstice and winter solstice, and also equinoxes, which mark the mid-points of this tilt where sunlight is just about equal all over the planet.
And it’s not just Earth that experiences seasons. Other planets do as well, although are often a little less tame than ours. On Mars, atmospheric pressure changes by 25% by summer and winter, and on Uranus, they are just coming out of winter after spending decades in it.
Is there a myth you’d like debunked? Email nicky@thejournal.ie
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