Coronavirus: week 1 thoughts

'In years to come, let them say of us: when things were at their worst, we were at our best.'

- Leo Varadkar, St. Patrick's Day 2020 television address

'History is new, my friends, and we are all of us making it, all the time, together.

- John Green, The Anthropocene Reviewed

'I never thought I'd say this, but I wish I was at school.'

- Philou, over bedtime milk and biscuits this evening

We don't want the aliens to think we're idiots

One morning this week little (no longer at all little) Philou asked me: 

'Dad, what's a parsec?'

Our conversations often begin like this, a subject coming out of the blue.

'It's a unit of distance', I said, delighted to have one of those increasingly rare moments with my children to show off my brilliance. 'A parsec is a few light years.'

This is the sort of topic I geek out on.

'You're wrong Dad, 'cos in Star Wars they use it to talk about time', he replied.

Well that can't be right. So we dug out the wikipedia article where it says plainly that a parsec is a unit of distance, and also that it's used incorrectly as a time unit in the first Star Wars film.

'So why do we need parsecs if we have light-years?', Philou continued.

'Well', I replied, 'if we were to meet aliens in a distant star system and tried to explain where we came from using light-years, they'd just think we were idiots!'

Imagine the conversation as humans encounter an alien on a faraway planet.

'We come in peace', our earthling spacemen might say.

'Cool! Where exactly do you come from?', the aliens might ask.

'Oh, a blue planet called Earth, a few light-years that way', we'd reply. 'You know, the distance light travels in a year'.

'The speed of light, gotcha', the aliens would say. 'That's a universal constant. But what's a year?'

Well that is indeed the killer question alright.

'A year is how how long it takes our planet Earth to orbit our sun. Well sort of, it actually takes a bit longer than that so every 4th year is 1/365th longer, called a leap year. But we don't use light-leap-years. Well actually we don't use years to measure light-years at all, we use metres per second. A metre is how far light travels in 1/1299792458th of a second. Seconds are 1/86400th of a day - a day is the time it takes our planet to rotate once on its axis. Well sort of, it actually takes a bit longer than that so we have leap seconds. So we've redefined a second as the ground state hyperfine transition frequency of the caesium-133 atom which in hertz is 9192631770 when...'

'Oh you guys are idiots!", interrupt the exasperated aliens. "How did you ever find your way here at all'.

And that's why we have parsecs. All our alien needs to understand is the concept of a circle and a little trigonometry, both probably understood by any intelligent life form, and then we can tell him how far away earth is in parsecs.

A parsec is the distance at which one astronomical unit subtends an angle of one arcsecond.

Like this:

How cool is that? (OK so there's teeny bit more complexity - see the parsec wikipedia article - but still!)

If you must know, a parsec is around 3.26 lightyears - but let's not go there again.