Ever since we figured out
that we live on a world bigger than what we could see,
our species has been exploring.
But the moment you leave home,
there’s this one really crucial thing you have to figure out:
Where am I now?
To modern eyes, it’s a simple question
because, you know…
But figuring out how to figure that out
has been one of the ultimate quests of human knowledge, like ever.
In the end, it took more than 400 years of experimenting
and even inventing whole new branches of science
in order to answer that question accurately.
And the most surprising connection
to come out of this epic scientific quest
—a discovery that all of us still rely on today,
is that knowing where you are
depends on knowing when you are.
Hey, smart people, Joe here.
嗨 《聪明刷》的观众朋友 我是Joe
So back in like fourth grade geography,
you probably learned about these lines
that crisscrossed the globe, right?
This whole time, this globe hasn’t had latitude and longitude on it.
I always keep a backup globe around.
Okay, the horizontal ones are latitude,
they tell you how far north or south you are from the equator,
which happens to be zero degrees latitude.
These vertical ones are longitude
which tell you how far east or west you are
from this line at zero degrees longitude,
which slices right through a little burrow of London called Greenwich.
There’s a reason why that is zero over all of these other lines,
because of a very particular scientific revolution
that took place right there.
This is a story that connects clock makers,
astronomers, sailors, mathematicians, kings and queens,
天文学家 水手 数学家 国王和王后
space satellites, and even smart bombs.
The discovery at the center of all of this
enabled the creation of the colonial empires
that shaped our modern world
by giving ships a more precise and reliable way
to navigate the open seas.
Speaking of navigation, how did people used to do that?
Latitude is actually pretty easy to find
’cause you can do it using the sun or other stars,
which humans have been doing for thousands of years.
Here’s just one way to do that
so you can see how simple it is.
The North Star is basically at a fixed point in the sky over the North Pole.
You can figure your latitude
by measuring how high it is in the sky.
At the equator, zero degrees,
it’s basically at the horizon in France,
it’s at about 45 degrees.
And at the North Pole,
it’s 90 degrees up above your head.
Congratulations, you can latitude.
People from the Phoenicians to the Polynesians
to early Hindu astronomers
developed their own tools
to interpret the position and movement of stars,
and figure out how far north or south they were.
That may even be how ancient aliens
help the Egyptians align the pyramids.
Who put that in the prompter?
That did not happen.
It wasn’t aliens.
But figuring out longitude is much more difficult
for a really obvious but kind of weird reason
because all of those reference points in the sky
that you want to use for measuring,
they’re moving too as the earth rotates.
The earth is spinning, which means the sun and the stars
move across the sky every day,
so you can’t just use their position to find
how far you’ve moved in the same direction.
But going back to ancient Greeks, like Ptolemy,
people figured out this pretty neat connection:
To find out how much you’ve moved east or west,
you just have to know how far in time you’ve moved.
Let me explain.
Our planet takes 24 hours to complete
one full 360 degree revolution,
which means each hour or 1/24th of a spin
represents 15 degrees of longitude.
If it’s 3:00 AM in London, and where I am
the clock says it’s only midnight,
I know that I’m three earth rotation hours away from London
and that means 45 degrees of longitude.
And since I’m earlier, that means I’m west.
If you know the time in two places,
you can figure out longitude.
It sounds simple because today
knowing exactly what time it is in two places at once is simple.
But getting accurate time 400 years ago
was anything but simple.
And trying to figure out a way that you could do that
on a moving ship in the middle of the ocean
stumped the brightest minds in the world for centuries.
The search for longitude was like
searching for the fountain of youth
or a way to turn lead to gold.
It was this almost mythical quest.
And then in the 1700’s, it got real.
So it’s 1707, and this British admiral
named Sir Cloudesley Shovell
is leading his fleet home after a little skirmish with the French.
Wait, is that his real name?
That sounds like the name you’d make up
to make fun of a pompous British admiral guy.
Okay, it’s real.
Okay, Sir Cloudesley Shovell,
he’d won the fight and were on their way home to celebrate
when it got really foggy.
And since back then to navigate out of sight of shore,
you needed to be able to see the sky,
this basically meant they had no idea where they were.
After 12 days in bad weather,
Shovell’s best navigators put their heads together
to try and figure out the fleet’s position.
Really the only option they had
was to rely on something called dead reckoning,
basically figuring out where you are
by estimating your speed and compass heading
to plot your journey.
But winds and currents, they make this pretty imprecise,
and they got it wrong.
One by one, four very expensive warships
crashed on the rocky coast of the Scilly Isles.
Wait, that’s their real name?
That sounds like the name you’d make up
to make fun of some very British islands.
So on the rocks of the Scilly Islands,
like 2,000 sailors died, making Shovell’s error
one of the biggest screw ups in the history of ocean navigation.
For early sailors,
mistakes like this could be deadly in more ways than one,
even if you didn’t crash,
unnecessarily long journeys
meant your crew might starve or get scurvy,
and nobody likes scurvy.
Plus because ships had to follow established routes,
that increased your chances of running into pirates or your enemies.
So in 1714, these misadventures
had proven just too much for the monarchy
and the British government set up a prize,
20,000 pounds to anyone who figured out
how to accurately find longitude at sea.
And you’re like, “Ooh, big deal, 20,000 pounds?”
你会说“哦 有啥大不了的 就两万英镑？”
Well, factoring in inflation,
the Longitude prize would be worth around 6 million today,
that’s like six times what you’d get for a Nobel Prize.
Figuring this out would save lives and money
but these Imperial Navys definitely also realized that
whoever was first to figure this out
would open up the world.
Now remember, people had been trying to solve this riddle
for a long time.
The biggest science brains of history had tried and failed
because no one could figure out
how you could accurately know what time it is
in some far off place.
Everyone trying to win the prize
basically settled on one of two strategies:
The first one, let’s call them Team Almanac,
realized if you and someone else
could both observe some astronomical event
at the same moment,
and you knew exactly when that event should happen,
you could figure out the time difference
between the two locations.
Let’s just say hypothetically,
every day at a specific moment, this one star turns purple
for exactly one second.
In London, we know that happens at 3:00 AM,
this is fake and doesn’t happen,
but it gets the idea across.
I’m sailing on a ship and wherever I am,
I look up and I see that star blink purple,
I check my local clock and it’s only 12 midnight.
Now I know that I’m three hours
of earth rotation from London, and like I said before,
that means I’m 45 degrees west of London.
So that is a completely made up example,
but thanks to astronomers watching the sky
and writing stuff down,
and thanks to all that math that people like Newton invented,
people had gotten pretty good at predicting the movements
of stars and stuff on future dates.
There were literal books
full of where different sky objects would be
at different times and dates.
But this was not easy.
Assembling all of that astronomical information
took literal decades of observations
and very complex calculations by hand
and your location was only as good
as the information in your little almanac.
All this precision astronomy was really new back then.
So if your little book was wrong,
your longitude calculation would be off too.
So the second team, let’s call them Team Clock,
said, “What if we could just make this easier,
cut out all that astronomical math stuff
and just carry an accurate clock
that always tells us what time it is
back at zero degrees longitude?
Then just compare that with your local time
and bam, you know your longitude.”
The thing is, keeping time on a ship wasn’t easy either.
You could figure out local time, wherever you were
by marking noon each day
by waiting for the sun to reach its highest point,
but knowing what time it was back in Greenwich, no way,
because clocks that kind of stunk.
Pendulum clocks, they don’t keep very good time at sea
because motion on the ocean messed with their swings
and their metal parts were sensitive to changes in temperature and pressure.
They’d slow down, speed up,
or sometimes just stop running entirely.
Mechanical clocks, the ones with springs and stuff
weren’t much better at the time,
a few weeks at sea with a bad mechanical watch
and your Greenwich time is wrong.
What they needed was to build a better clock
than anyone had ever built.
And the person who finally did that was a carpenter
from Nowheresville, England.
John “Longitude” Harrison.
I have no idea if they actually called him that,
but they probably should have,
he really has a nice ring to it.
No one really knows how John Harrison
got so good at making clocks,
but he was a self-taught timekeeping genius.
You could say he was the first big TikTok-er.
After like 40 years of tinkering and prototyping,
Harrison built a clock based around a spring
made from this new kind of steel
and these low friction bearings made from literal jewels and gems.
When it was tested at sea,
it didn’t lose more than a second over a whole month.
Even the most expensive Swiss watches today
can drift by seconds every 24 hours.
So Harrison’s marine chronometers
were some of the most precise machines ever built.
And ultimately he ended up winning the Longitude Prize.
Their new longitudinal prowess gave British sailors
an advantage when it came to navigation
and was not a small reason
their flag came to dominate the globe.
And meanwhile, all the cutting edge astronomical work
happening at the Royal Observatory
and the fact that they were in charge of the Longitude Prize
put Greenwich on the map for all of history
when that meridian was officially named
Zero Degrees Longitude.
I mean, think about it,
unlike the equator for latitude,
zero degrees longitude could technically be anywhere, right?
But because of all of this history,
this line is where longitude is measured from today.
Most people don’t think about longitude much today
but it unlocked this really strange idea
that had been floating around since the ancient Greeks.
Knowing when you are can tell you where you are.
And this same idea is why every time you open your phone up
and look at a map, you know precisely where you are.
The GPS satellites orbiting our planet
send out time coded messages.
When one reaches a GPS receiver,
it compares its local time to the time that message was sent.
And since it traveled at the speed of light,
it can calculate you are somewhere on a sphere
a certain distance from that satellite.
Do that with three or four satellites,
it’s enough to pinpoint your position
to one particular spot on the globe.
This key connection between time and location
underlies so much of our modern life,
from mighty military machines
to simply meeting your mom for a mocha.
Those clocks today might be atomic
rather than run on gears and springs,
but it relies on that same key connection,
knowing when you are, can tell you where you are.
Thanks for watching,
and I’ll see you next time, wherever that is.
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See you later, phew, phew.
回见 咻 咻
You know one cool Patreon perk we have
is the ability to send in a dad joke for me to read.
Like why am I always sitting on my watch?
So that I’m on time, from meeting a friend for coffee
to, well, dropping smart bombs.
See you next time, wherever that is.
Ever since we figured out