‘Excuse me, Andrew?’

‘Yes, Rodrigo?’

Andrew stopped listening to Marcia and Monica’s conversation and turned his attention to Rodrigo who was sitting between his Mum and Andrew. Marcia sat on the other side of Monica at one of the round tables in Mary’s Trattoria, a restaurant serving Italian cuisine, where they were all waiting for dinner to arrive.

‘I read about the Concorde on the Wikipedia and I have a question…’

‘That’s good. What’s bothering you?’

‘Well,’ said Rodrigo, ‘I read that when flying on Concorde you could see the sun rise in the west. How can that happen when the sun always rises in the east?’

‘I am glad you asked, because that’s a good question. Let me think about an answer for a moment. Here comes our dinner…’

The waiter bustled from the kitchen bearing plates of steaming food on a tray, which he carefully balanced on the edge of the table. He placed lasagne in front of Marcia; to Monica he gave the fettuccine Alfredo; before Rodrigo he placed the spaghetti Bolognese; to Andrew he gave a dish of spaghetti marinara.

‘Oh!’ said crestfallen Rodrigo. ‘How do I eat this?’

‘Watch me,’ said Andrew as he plunged his fork into his spaghetti marinara and gave it several deft twists with the fingers of his right hand, then lent forward over his plate and lifted the spaghetti entwined in the tines of the fork to his mouth, leaving several spaghettis trailing from his mouth to the plate, which he sucked up with a slurping noise; as the spaghetti disappeared they lashed to and fro leaving streaks of marinara sauce on his face.

‘There. That’s how you eat spaghetti,’ said Andrew as he wiped his face with his napkin. ‘Fun, isn’t it?’

Grinning, Rodrigo soon learned how to eat spaghetti with gusto. Monica sent him to the bathroom to wash his face afterwards…

‘…Now then, let’s see if we can answer your question while we wait for our dessert and coffee,’ said Andrew taking his notebook and pencil from his pocket. ‘Today, it is generally accepted by scientists that the Earth rotates on its axis and that the Earth orbits the Sun, which is in a fixed position in space. This is what we will assume for the purpose of getting an answer to your question. Are you happy with our assumption?’

‘Yes…, I think so.’

‘Good! So, what causes day to follow night: the rotation of the Earth or the orbit of the Earth around the Sun?’

For a moment, Rodrigo thought and then said: ‘The rotation of the Earth.’

‘Correct. Here is what it looks like,’ said Andrew as he drew a diagram on a blank sheet of his notebook. We are looking down on the north pole. That stick-figure represents you farther south, standing outside at Heathrow Airport, London, looking towards the north pole; to your left is West to your right is East. We agreed that the Sun is fixed in one position and that the Earth revolves. As you can see, I have drawn you on the other side of the planet to the Sun. Is it day or night where I have shown you standing?’

‘Night.’

‘Yes, correct. So, as we look down on the north pole, which way does the Earth rotate for the sun to appear to rise in the East, clockwise or anticlockwise?’

Rodrigo looked at the picture then said: ‘Anticlockwise.’

‘Correct. Well done. Now, having just seen the Sun rise in the East, you continue standing there for a few hours and see the Sun apparently rising higher in the sky, passing overhead, and start setting towards the West. Correct?’

‘Um… yes.’

‘Now you’ve seen the Sun set in the West and it is now dark. Next, you board Concorde at Heathrow Airport in London. You take off and fly West towards America. Remember that the Earth is rotating anticlockwise to the East. The pilot of Concorde climbs to cruising altitude at 60,000 feet and engages the engine afterburners to go supersonic. Eventually, you will see the Sun again as it rises in the West because, in Concorde, you are now flying faster than the Earth is rotating.’

‘No way!’ exclaimed an incredulous Rodrigo. ‘You can’t fly faster than the Earth rotates.’

‘You don’t think so?’

‘No, you can’t— Can you?’ Rodrigo started to sound uncertain when he saw the gleam in Andrew’s eye and slight upward twitching of the corner of his mouth.

‘Ah! Well, we can calculate the speed at which the Earth rotates, can’t we?’

‘Can we?’

‘Of course. You are already halfway there…’

‘I am?’

‘Don’t you remember the last time we dined together, you calculated the circumference of the Earth?’

‘Yes, but what’s that got to do with it?’

‘Everything,’ said Andrew as a broad grin spread across his face. ‘At least, half of everything. Here is your dessert. Consider what you know while you eat your ice cream.’

Andrew gave Rodrigo a reassuring smile as he raised the steaming cup of coffee with chicory to his lips and sipped while watching Rodrigo prolong his encounter with dessert…

…Rodrigo pushed away his empty bowl and sighed. Andrew set his cup and saucer to once side and then reached into a capacious pocket further down on the leg of his trousers and produced a calculator.

‘You have a calculator with you!’ said Rodrigo in surprise.

‘Only when I am having dinner with you. This will save us arithmetic drudgery and let us concentrate on the more interesting problem of finding out how fast the Earth rotates.’

‘But, I don’t know,’ said Rodrigo with a frown.

‘Yes you do. You’re halfway there already, like I said. I only have to ask you a few more questions to get the answer. Let’s begin.’

‘OK!’

‘How many hours are there in a day?’

‘That’s easy, twenty-four,’ Rodrigo said immediately.

‘So how many revolutions of the Earth happen in one twenty-four-hour day.’

‘One.’

‘So, if it takes twenty-four hours for the Earth to make one revolution, how far is that?’

‘I don’t know.’

‘Would it be the circumference of the Earth?’

After a moment of thought, Rodrigo said: ‘Oh! Well, yes.’

‘Remember the calculation you made of the circumference of the Earth last time we met. How far around is the circumference of the Earth?’

‘Of course, it is 21,600 nautical miles. I remember.’

‘Yes, you do. So one revolution of the Earth represents a distance of 21,600 nautical miles, right?

‘Yes.’

‘So, if a spot on the Earth moves through 21,600 nautical miles in 24 hours, how fast is it moving?’ said Andrew as he offered the calculator to Rodrigo.

‘That’s easy. I just divide 24 into 21,600.’

‘Precisely. Now give me an answer.’

Rodrigo pushed the buttons on the calculator and showed Andrew his result: ‘900.’

‘That’s correct, 900 knots. Now we must convert knots to miles-per-hour. Remember that I said nautical miles are longer than statute miles, so for a conversion factor divide 6060 feet by 5280 feet and then multiply the answer by 900 knots.’

Rodrigo worked the calculator and showed Andrew his result: ‘1,032.95’

‘We can round the number to 1,033 miles-per-hour. Concorde’s maximum cruising speed is about three hundred miles-per-hour faster than the rotation of the Earth, which means that by flying West just after sunset, you will eventually catch up with and see the Sun rise in the West. Amazing, isn’t it?’

‘Yes. I wish I could fly on Concorde,’ said Rodrigo wistfully.‘

Sadly, you can’t anymore. But, you could be a supersonic fighter pilot when you are old enough.’

‘Can I?’

‘Of course, but you must be physically very fit, intelligent, and capable of dividing and prioritizing your attention in a demanding environment.’

‘Could you have been a fighter pilot?’

‘Oh no!’ said Andrew. ‘Not at all. I don’t have the personality of a fighter pilot. I’m an engineer. Engineers have great powers of concentration. I wouldn’t last long in a jet aircraft; I wouldn’t be able to keep up with the rapidly changing events.’

‘Being a fighter pilot sounds like a lot of fun,’ said Rodrigo. ‘I might try that.’

‘Well think about it. Here’s the check. I think it is time for us to go.’

The waiter brought the check to Andrew, who paid the bill.

‘I hope you had a good summer, Rodrigo. Have a safe journey home.’

‘I did, thank you. Goodbye, Andrew.’

‘Goodbye, Rodrigo.’