WEBVTT
Kind: captions
Language: en

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I am squinting into the sun at the sundial
at the Olympic Park

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and this is a gorgeously designed sundial.

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Because not only is the user the gnomon, the post for the sundial,

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so my shadow is reading 11 o'clock

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and that is pretty much accurate,

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it also has GMT and BST so the summer months still have the correct time.

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And it has the equation of time built into it.

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Now the equation of time, the name sounds like pseudo-scientific rubbish, but it isn't.

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It's an equation in the old fashion sense of "to make equal".

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See, there are two different types of time, if you like.

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There is solar time, that is, the time that means that noon is when the sun is highest in the sky.

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And then, there is mean time. Clock time,

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a kind of averaged, ideal time

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where noon falls reliably every twenty-four hours.

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And, well, there is a distinction between the two.

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Because look down at my feet,

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June is now so I am standing here.

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Were it March or September,

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I'd be standing here.

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And that is because the sun would be in a different position in the sky. It would be lower.

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Because a) The Earth is tilted because of the seasons.

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B) earth orbit is an ellipse not a circle.

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So I'd be standing here, the sun would be in a different position,

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but my shadow would still read 11.

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And if it were January or December in the depths of winter,

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I'd be standing here, and my shadow would still be-

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Well actually, the olympic stadium would be covering up the sun.

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So my shadow wouldn't be anywhere.

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But were there theoretically a shadow,

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it would still hit 11.

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And the interesting thing about that is that sundials have only been fitted with this in the last couple of centuries.

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You see, it used to be that sundials
were *the* accurate record of time.

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When the sundial said it was noon

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the sun was the highest in the sky, and it was noon.

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No matter the time of year.

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And then along came reliable clocks

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and later the railways and telecommunication.

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The requirement for different bits of the country

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to be on the same time,

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to have the same noon.

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So it went from sundials being accurate

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and mechanical clocks always being a little bit out...

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to mechanical clocks being accurate

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and sundials always being a little bit out.

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And you can find from a few centuries ago,

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things called equation clocks.

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Perfectly accurate clocks, reliable 24 hours in a day clocks, more or less.

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That would deliberately change their time

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either by a complicated clockwork mechanism

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or by the user changing something.

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So that they were acurate to the sundials

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and not the other way round

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Because sunrise in the east could be 20 minutes, 25 minutes

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ahead of sunrise in the west of Britain.

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So there you go: the equation of time.

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It's a thing that means sundials aren't accurate anymore,

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even though once upon a time they always were.

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Something you might not have known.

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English Subtitles by: UndeadDog