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I thought it would be fun to ask Twitter what space fact they would tell kids aged 7. Today I spoke to a class of young children about the Solar System and managed to get a few of these into my hour.

I rather enjoyed the various responses and thought they might inspire more in turn. So here’s a collection of things astronomers would tell very young children. Feel free to tweet me @orbitingfrog with more!

“You can fit over 1,300 Earth sized things inside Jupiter but over 1,300,000 Earth sized things inside our Sun. Stuff is huge!” – Megan Whewell

“If you drove to the sun it would take 152 years.” – Alistair Gibbs

“That [space is] all a big nothing.” – Erik J Cox

“[There’s] more water on tiny Europa than there is on earth” – Ian in Brighton

Io smells like rotten eggs because of the sulphur volcanoes. Stinkiest place in the Solar System?” – We Are All in the Gutter

“The giant planets have likely moved and Neptune and Uranus might have switched places.” – Meg Schwamb

“Tell them that dwarf planet Ceres was once a planet too & survived the downgrade to asteroid status.” – Richard Drumm

“You could float Saturn in the bath. If you had a Saturn-sized bath.” – Jim O’Donnell and John Hicks

“If the sun is a big beach ball, then the Earth is a small marble about a football field away” – Michael Nielsen

“[There’s] Red helium-neon rain on Jupiter and metallic snow/frost on Venus” – @blobrana

“The rain on [Saturn’s moon] Titan is flammable (but there’s no oxygen there so it never burns).” – James O’Brien

NOTE: I’ll add more as they are Tweeted

Answers for Allensbank

February 1, 2010 — Leave a comment

The other week I gave a talk at Allensbank Primary School – a nearby school for children aged 4 to 11. I mainly told them about the planets and the Solar System but obviously we got onto other topics too. We had a fun questions and answers session at the end but there is never enough time – in light of this many of them sent me letters with more questions.

What is Your Favourite Planet?

Shaheer, Esme and Thea all want to know what my favourite planet is. It’s an important question. At first I want to say that the Earth is my favourite planet but that’s cheating, isn’t it? In which case, I think it has to be Jupiter.

Jupiter Through a Telescope

Jupiter was one of the first planets I looked at through a telescope (I was 12) and when you do that you can see that it has four very bright moons. These moons are called the Galilean Moons because they were observed by Galileo, the first man to look at the sky with a telescope – and that was 400 years ago! You can also sometimes see that Jupiter is stripy and that it has a big, red spot. Saturn is also good to look at  – with its bright rings – but Jupiter changes every night, which is very cool and interesting. The moons move and the stripes and spot rotate around the planet.

Why are There Craters on the Moon?

Sean asks why there are craters on the Moon. The answer is that that space is not empty. The Solar System is a very busy place. As well as planets and moons and the Sun, there are also other objects in the Solar System. yoiu might remember I talked about comets and asteroids. These are rocky bodies, smaller than planets, that also go around the Sun. There are also even smaller rocks out there, flying around. Quite often these rocks hit the larger planets and moons. The craters on the Moon are the left over pock-marks from rocks hitting the surface of the Moon.

We see craters all over the Solar System. Mercury and Mars are covered in them, and so is any other object that is rocky and not covered in clouds. Even the Earth is hit by rocks sometimes. We can see some craters here on Earth! They are harder to find because of all the grass and volcanoes and glaciers and rivers covering them up – but sometimes they are found. They can be very big!


There is a very big crater in Arizona in the USA called Barringer Crater – I have put a picture of it here for you. It is 1,200 metres across (nearly a mile) and it was formed 40,000 years ago when a 50-metre wide rock crashed into the Earth from space.

You can play with a fun Earth-smashing, asteroid simulator called Down2Earth. It lets you try and smash all sorts of different sizes of rock into the Earth and see what damage they would do.

Living on Other Planets

Thea asks whether people live on other planets. Currently no, they don’t. People do live in space now. There is always a crew onboard the International Space Station. New astronauts arrive to change-over roughly once every six months.


A lot of people think we should go back to the Moon one day and set up a Moon base so that we can learn how to live on other planets and maybe mine the Moon for minerals – like we mine the Earth. Living on the Moon might mean that we can figure out how to go and live on Mars one day too.

I’ll leave it there for now. I have more questions to answer but I’ll leave that for part 2. A lot of you said how much you liked the images of the nebulae that I showed you. At the top of this post you’ll see a lovely picture of the Orion Nebula from the Seeing in the Dark website.

I recently did a piece on measuring the speed of light using your microwave. Well here is some more physics you can play with in your kitchen. This time let’s create a vacuum and then use it to crush something. I like crushing things. Don’t we all?

What you will need:

  • A regular drinks can
  • A pot of cold water big enough to submerge the can
  • A pair of tongs
  • A kitchen hob (gas or electric is fine).

What to do:

Now you have to be careful with this one. The tongs have to be good or you’ll burn yourself. If you’re a child reading this, then make sure someone supervises you while doing this experiment. Reading though all the instructions before you start out is vital. I recommend having a couple of attempts, so maybe have two or three cans ready. So let’s begin:

Whilst you are filling up the pot of water why not drink the coke or whatever is in your drinks can. We don’t need any of the contents for this experiment, just an empty can. Once it is empty, rinse it out and place about two tablespoons of water in the can.

Now take your tongs and get a firm hold on the can. Hold it over the kitchen hob. We need to boil the small amount of water we have put in the can. This won’t take long and you’ll know when it’s worked because you’ll see steam coming out of the hole at the top of the can. Let it steam for a minute or two to be sure the water has all boiled.

Now here’s the cool bit. Keeping the can in between the tongs, take the can directly from the hob and dunk it, upside down, into the pot of water. The can will instantly and violently be crushed! It will happen very quickly so be ready. When I did it, it made a loud smacking sound as it went under water. I did it twice because I missed it the first time!

What is happening?

There is some great physics going on in this simple experiment. When you heat up the can and boil the water inside, the can fills with steam and pushes out all the air. Then when you dunk the can into cold water, the steam quickly condenses into water and there is no air pressure inside the can to support it. The can cannot resist the forces pushing on all sides from the water and air above it. Therefore it is crushed instantly!


Air pressure is also at work in balloons. When you blow air into a balloon you are artificially increasing the air pressure inside it and the rubber skin expands outward, forced by the force of the air molecules bounding around inside it.

You can ‘crush’ balloons by dipping them into liquid nitrogen. This condenses the air inside into a liquid and the balloon goes flat as a pancake. Here can see a video of a balloon that has been dunked into liquid nitrogen thawing out. The air boils back into a liquid and the balloon re-inflates. We filmed this last year in our first year undergrad physics lab.

Enjoy playing with air pressure and feel free to send me any images of your crushed cans!