Astronomical twilight times

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Astronomical twilight times

Postby ed_b » Sun May 15, 2016 5:30 pm

Hi folks,

Reposting this here after galileo's advice:

I'm completely new to astronomy and although I love looking at the night sky my query is not quite about looking up at it so much as how astronomical phenomena vary through the year.

2016 Chart 2.png


I need to know astronomical twilight times (ie, sun's depression 18deg). I've graphed the data from HM Nautical Almanac Office and have a puzzle.

The lines for sunrise/sunset are nice smooth sine waves (or as close as I can get Excel to mimic these).

But, as well as astro. twilight not occurring at all around midsummer (as expected), speed of change in astro. twilight times seems to accelerate massively just before and after it stops occurring. It seems not to follow the sine rule (?)

Can anyone explain? Surely HMNAO doesn't have their algorithm wrong?

Thank you!

(The graph is for Peterborough, btw)

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Re: Astronomical twilight times

Postby Bizibilder » Sun May 15, 2016 9:40 pm

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Re: Astronomical twilight times

Postby ed_b » Mon May 16, 2016 1:20 pm

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Re: Astronomical twilight times

Postby Bizibilder » Mon May 16, 2016 5:05 pm

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Re: Astronomical twilight times

Postby galileo » Mon May 16, 2016 5:19 pm

Last edited by galileo on Thu Aug 17, 2017 8:33 am, edited 1 time in total.
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Re: Astronomical twilight times

Postby ed_b » Mon Aug 14, 2017 4:32 pm

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