How long does it take the Sun to cross the sky?

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Ighsaan

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How long does it take the Sun to cross the sky?
« on: 02/09/2008 17:53:51 »
Ighsaan asked the Naked Scientists:

How long does it take from the time that the sun touches the horizon to the time it disappears below the horizon at sunset?

What do you think?

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Offline Soul Surfer

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How long does it take the Sun to cross the sky?
« Reply #1 on: 02/09/2008 23:24:02 »
The length of time it takes can vary from a small value to a very long time depending on the angle that the sun is crossing the horizon.  

Let us first look at the mininmum in the tropics where the sun can set vertically down from the horizon. Neglecting the effects of atmospheric refraction the diameter of the sun is half a degree and the sun moves fifteen degrees an hour (360 / 24) so the sun sets in on thirttieth of an hour or two minutes.  Whereas at the north pole the sun circles the horizon at the same level and so   it sets as its latitude drops half a degree below the equator which takes about 48 hours.
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Offline turnipsock

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How long does it take the Sun to cross the sky?
« Reply #2 on: 02/09/2008 23:58:46 »
Do you not have to take into account the size of the sun?

The bit we see rising first is not the same bit as we see setting last. So even at the equator, at the equinox, the sun will be in the sky for more than 12 hours.

(That is unless, we are treating the sun as a point.)
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Offline Soul Surfer

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How long does it take the Sun to cross the sky?
« Reply #3 on: 03/09/2008 23:42:05 »
Turnipsock the day is extended by much more than this because the deviation at the horizon due to atmospheric refraction is about three degrees or six times the width of the sun.
Learn, create, test and tell
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lyner

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How long does it take the Sun to cross the sky?
« Reply #4 on: 03/09/2008 23:51:07 »
Your personal horizon is affected by your altitude, remember.
Nautical Almanacks have the specific information you want which takes everything into account - latitude, altitude, day of the year etc..

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Offline LeeE

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How long does it take the Sun to cross the sky?
« Reply #5 on: 05/09/2008 00:59:12 »
Umm...

just thought I'd point out that it's the horizon touching the sun rather than the sun touching the horizon.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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lyner

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How long does it take the Sun to cross the sky?
« Reply #6 on: 05/09/2008 12:04:33 »
you mean Plato is wrong?

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Offline LeeE

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How long does it take the Sun to cross the sky?
« Reply #7 on: 06/09/2008 14:48:48 »
I believe 'was' is the correct term.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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lyner

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How long does it take the Sun to cross the sky?
« Reply #8 on: 06/09/2008 20:36:30 »
is he not arround then?
I thought I saw him in Sainsbury's the other day.

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Offline LeeE

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How long does it take the Sun to cross the sky?
« Reply #9 on: 07/09/2008 13:02:26 »
Probably just someone from one of those celebrity look-alike agencies doing their shopping.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!