I am squinting into the sun at the sundial at the Olympic Park
and this is a gorgeously designed sundial.
Because not only is the user the gnomon, the post for the sundial,
so my shadow is reading 11 o'clock
and that is pretty much accurate,
it also has GMT and BST so the summer months still have the correct time.
And it has the equation of time built into it.
Now the equation of time, the name sounds like pseudo-scientific rubbish, but it isn't.
It's an equation in the old fashion sense of "to make equal".
See, there are two different types of time, if you like.
There is solar time, that is, the time that means that noon is when the sun is highest in the sky.
And then, there is mean time. Clock time,
a kind of averaged, ideal time
where noon falls reliably every twenty-four hours.
And, well, there is a distinction between the two.
Because look down at my feet,
June is now so I am standing here.
Were it March or September,
I'd be standing here.
And that is because the sun would be in a different position in the sky. It would be lower.
Because a) The Earth is tilted because of the seasons.
B) earth orbit is an ellipse not a circle.
So I'd be standing here, the sun would be in a different position,
but my shadow would still read 11.
And if it were January or December in the depths of winter,
I'd be standing here, and my shadow would still be-
Well actually, the olympic stadium would be covering up the sun.
So my shadow wouldn't be anywhere.
But were there theoretically a shadow,
it would still hit 11.
And the interesting thing about that is that sundials have only been fitted with this in the last couple of centuries.
You see, it used to be that sundials were *the* accurate record of time.
When the sundial said it was noon
the sun was the highest in the sky, and it was noon.
No matter the time of year.
And then along came reliable clocks
and later the railways and telecommunication.
The requirement for different bits of the country
to be on the same time,
to have the same noon.
So it went from sundials being accurate
and mechanical clocks always being a little bit out...
to mechanical clocks being accurate
and sundials always being a little bit out.
And you can find from a few centuries ago,
things called equation clocks.
Perfectly accurate clocks, reliable 24 hours in a day clocks, more or less.
That would deliberately change their time
either by a complicated clockwork mechanism
or by the user changing something.
So that they were acurate to the sundials
and not the other way round
Because sunrise in the east could be 20 minutes, 25 minutes
ahead of sunrise in the west of Britain.
So there you go: the equation of time.
It's a thing that means sundials aren't accurate anymore,
even though once upon a time they always were.
Something you might not have known.
English Subtitles by: UndeadDog