Primary Science Workshops

Primary school science workshops with a WOW!

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BITESIZE SCIENCE: Why do we have seasons?

The seasons are different periods of the year with varying temperatures and weather patterns, called Spring, Summer, Autumn and Winter. The reason we have seasons is because the Earth’s axis (which is the middle of the line down which it spins) isn’t straight, it’s tilted.

 

Because the Earth’s axis is tilted, some parts of it are closer to the sun at certain points during the Earth’s orbit. For instance, in June, the top half of the Earth, called the northern hemisphere, is closer to the sun than the bottom half, the southern hemisphere. Even though the entire Earth is the same distance to the sun that it always is, we experience summer because of this, though someone should probably tell our rain clouds!

What are the seasons? 

(Teachers, this article is great preparation for our Rockets to Rovers school space workshop)

why do we have seasons

How did the Earth become tilted and why is this a good thing? 

The reason that the Earth is tilted is thought to be because billions of years ago a huge object like an asteroid, about the size of Mars, collided with the Earth, tilting it by about 23.5 degrees.  The resulting seasons happen to be pretty great for the development of life, which likes a variety of different weather, from sunshine to rain.  

 

This means that not only can we grow crops in a nice cycle at different places and at different times around the world, but we can also enjoy the massive variety of wild plant-life and animals that we find on our colourful planet, which are all adapted to different temperatures and weather patterns.  In fact, given that the conditions had to be perfect for a world such as ours, you might consider yourself very lucky to be born here instead of one of the other estimated 40,000,000,000,000,000,000,000 planets in the universe, which we actually spell out in our rocket workshops with pupils holding a 4 and 22 zeros!

 

But the tilt of the Earth isn’t the only reason we were so lucky.  It just so happens that we are in what scientists call a ‘Goldilocks spot’ which is a distance from the sun that is so perfect for the growth of life that it is ‘just right’, exactly like Goldilock’s porridge!

The quick answer is yes they do, though they might look and feel very different to our seasons on Earth, because their orbits and tilts are all very different to ours.  

 

For example, you would think that the closer they get to the sun the hotter they would normally get, right? But, no, like a lot of science, it’s not that straightforward.  Neptune, for instance, our furthest official planet from The Sun (not including Pluto) can be as cold as 200 degrees Celsius on its surface, but its core is a whopping 7000 degrees!  Which is actually about 1500 degrees hotter than the core of Earth and hotter than the surface of the sun itself!  Phew.  This is because Neptune is about 17 times the mass of Earth so the friction created inside of it when it spins is much greater.   Now rub your hands together until they get warm.  See what I mean?  When surfaces rub together they create heat because of friction.  Now imagine many billions of hands rubbing together and it might give you an idea of why Neptune’s core is so hot!  The effect of this is gigantic storms on the icy planet’s surface.

Do the other Solar System planets have seasons? 

neptune

Neptune

In our primary space workshops we often ask pupils 'Which planet is the hottest?' to really make them think about planetary science.  So what would you answer?  Would you say Mercury, the planet closest to The Sun?  If so you would be wrong, and let me explain why.

 

It helps to know that Mercury spins very slowly, taking about 60 times as long to rotate as Earth does. which means that it’s often very cold on one side and very hot on the other, for very long periods of time.

 

Because of this Mercury has almost no atmosphere, which stops it getting the 'hottest planet' prize.  Now, compare this to our most excellent atmosphere here on Earth. Think of it as a thick layer of gases that surrounds our planet like a great big blanket, keeping us warm all around so that life on Earth can exist.   Compared to us, Mercury is more like the kid who forgot to bring his blanket to the sleepover and has to use a scruffy old Thundercats blanket you have had stored in the cupboard with no stuffing and holes in it!  The result of this is that almost all the heat is lost from Mercury back into space after its hot daytime ends.  Don’t get me wrong, Mercury is still very hot though.  The side facing the sun can get as hot as 426 degrees Celsius, but the side not facing the sun can get as cold as -173 degrees Celsius! Yep, that’s almost as cold as Neptune!

 

So, which planet is the hottest then? That’s good old Venus, the second planet from The Sun.  Because of its protective atmosphere, Venus is the kid whose Mum is overprotective and packed him four different blankets and a sleeping bag!  This atmosphere keeps it the same temperature all over, which is a cosy 460 degrees Celsius.  Just goes to show, Mum knows best! Except that planets don’t really have mums because they’re big balls of rock and gas flying through space around a giant ball of thermonuclear reactions!

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