‘My name is Megernicus!’ This time my voice comes out way too loud, a yell really, and a baby starts to whimper. How has this happened? Grandad promised me that I wouldn’t have to say a word and now I’m shouting at people!

Yay-Girl’s eyes go wide. ‘You’re called Mega Knickers? Cool!’

‘No, Megernicus,’ I say, but I’m wasting my breath because now all children are shouting out ‘Mega Knickers’, although some are just yelling ‘knickers’ and one boy is saying, ‘Willy, willy, willy,’ again and again.

I look at the entrance to the tent, but there’s no sign of Grandad. Now the children are laughing and pushing each other and a couple have even got to their feet. Their parents are looking at me with a mixture of sympathy and irritation.

This is a total disaster. I have to do something!

I force myself to think of the coolest, calmest person I know: Valentina Tereshkova. Not only was she the first woman to go to space, but before that she was a parachutist. She must have felt this fear, when you’re standing on the edge of something and you know you have to jump. I picture her strong, steady gaze. If Valentina could throw herself out of a plane repeatedly, then orbit Earth forty-eight times, then I can open my mouth and tell these kids about space.

So I take a deep breath, look at the chattering, squirming children, and I open my mouth. ‘That’s right,’ I say, raising my voice so it cuts across the talking. ‘I am Mega Knickers, and it’s actually a very common medieval name. Now, my grandad thinks that the sun is at the centre of the universe so we’re going to prove him wrong.’

‘What?’ Grandad walks back in with Elsa’s wriggling in his arms. ‘You’re talking nonsense! I tell you, the sun is smack bang in the middle of things.’

‘Not true,’ I say, smiling with relief. I wait for Grandad to join me at the front, but he just holds up Elsa and shrugs. Suddenly, I don’t want him to come and take over. I want to finish what I’ve started. I look back at the notes then hold up a roll of toilet paper. ‘Who knows how to use this?’ All around me hands shoot up, and children laugh, and that laughter helps me stand a little taller and clear my throat.

‘Good,’ I say, ‘because we’re going to use this toilet paper to learn how vast our solar system is, and this should help us understand the immense size of the universe.’ I turn to Grandad. ‘The sun is huge, Grandad Copernicus, but it’s just one of over one billion trillion stars in our universe and not nearly as special as you think.’

Soon we’ve unravelled the toilet roll and it’s snaking out of the tent and into the courtyard; children are running around with melons, apples and grapes, trying to work out where the ‘planets’ should go. I’m so busy answering their questions and trying to stop them from eating the fruit that I haven’t got time to think about what I’m doing. ‘Everyone go and stand near Earth,’ I say, ‘but don’t tread on it!’