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Why do we have seasons?

Misconceptions mean that a demonstration involving models of the Earth and Sun is required to help students understand
Nadiyah and her cousin, Sebastian, are both looking forward to their December school holidays. For Nadiyah, the freezing cold weather means it’s the perfect time of year to go sledding with her family, drink hot chocolate, and cuddle up by the fire to keep warm. For Sebastian, the hot, sunny days means that his family will be enjoying barbecues, playing at the beach, or splashing about in the pool to cool down. But how is it possible for Nadiyah and Sebastian to experience different seasons at the same time? To answer that, we need to learn about the seasons and why we have them. Let’s take a look at the Earth as it makes its way around the sun. A bit closer. Closer. Closer. Whoa.
Not that close. Back up a bit. Perfect. The Earth doesn’t stand straight up as it orbits the sun. Its axis is tilted at an angle of 23.4 degrees. This means that at certain times during its orbit around the sun, one hemisphere points towards the sun while the other hemisphere points away from the sun. When a hemisphere is pointing towards the sun, it receives lots of direct sunlight. This raises the temperature, causing the hemisphere to experience summer. The opposite is true for the hemisphere pointing away from the sun. That hemisphere doesn’t receive as much direct sunlight, so the temperature drops, and that hemisphere experiences winter. June marks the beginning of summer in the Northern Hemisphere and winter in the Southern Hemisphere.
Six months later, when the Earth reaches the opposite side of the sun, summer begins in the Southern Hemisphere while winter begins in the Northern Hemisphere. As the Earth travels around the sun, there are times when neither hemisphere is pointing towards or away from the sun, giving us autumn and spring. What does this all mean for Nadiyah and Sebastian? Well, they’re experiencing opposite seasons because they live on opposite hemispheres. Sebastian is pointing towards the sun in December, so he’s in the Southern Hemisphere, while Nadiyah is pointing away from the sun and freezing away in the Northern Hemisphere. But what about her cousin, Eduardo, who lives on the equator? It doesn’t matter which hemisphere is tilted towards the sun.
The equator receives the same amount of sunlight throughout the year, so the temperature there remains fairly constant. Some of the other planets of the solar system have seasons too. It all depends on their tilt. Some planets, like Venus, have almost no tilt and almost no seasonal changes, whereas the planet Uranus is so tilted that it barrel rolls around the sun, and seasons vary wildly depending on where on the planet you are. The further away from the sun you go, the longer it takes the planets to complete an orbit, and so the longer the seasons are.
If you’re ever unlucky enough to be stuck on Neptune during winter, make sure you’re wrapped up warm because you’ll have to wait 40 years for it to end. Brr!

It is a question that can make even the most experienced educator break out into a sweat – why do we have seasons?

Although the answer itself is fairly straightforward, the many misconceptions surrounding the seasons often mean that a demonstration involving models of the Earth and Sun is required to help students fully understand this topic.

Because we always get questions about the seasons, and we know that teachers do too, we decided to create an animated video that dives into this topic.

Key points

Key points covered in the video above are:

  • Different hemispheres experience different seasons at the same time.
  • The Earth is tilted by an angle of 23.4 degrees.
  • Due to this tilt, at some positions in the Earth’s orbit around the Sun, one hemisphere (northern/southern) points towards the Sun while the other hemisphere (southern/northern) points away from the Sun.
  • The hemisphere pointing towards the Sun receives more direct sunlight causing the temperatures to increase – that hemisphere experiences summer.
  • The hemisphere pointing away from the Sun receives less direct sunlight and so the temperature drops – that hemisphere experiences winter.
  • Autumn and spring occur when neither hemisphere points towards nor away from the Sun.
  • Temperatures along the equator are fairly constant throughout the year because the amount of direct sunlight that falls on the equator is constant.
  • Some of the other planets in our solar system experience seasons.

Common misconceptions

Students are not the only ones who have misconceptions about the seasons; many adults have the same misconceptions too.

Here are a few of the misconceptions that pop up during sessions with students and members of the public:

  1. The Earth’s orbit is highly elliptical with the Sun noticeably off-centre.
  2. We experience summer when the Earth is closest to the Sun and winter when it’s furthest from the Sun.
  3. Both hemispheres on the same side of the Earth experience the same seasons at the same time. People living on the other side of the Earth experience the opposite season.
  4. The Sun’s temperature changes throughout the year, which causes the seasons.
  5. If they know the Earth is tilted, they think the tilt causes the Earth to be considerably closer to the Sun at some points in its orbit.
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Physics, Astronomy, and Space: Teaching Secondary Science

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