Thanks all for responses. They have all been helpful. The above link says You can, of course, spend a lot of time and effort downloading and installing CPAN astronomical modules to calculate the time of sunrise and sunset, and reading manuals and doing a whole lot of stuff. But if you are content with approximate times, you can use some delightful shortcuts. I spent that time having every advantage. It did take north of an hour to happen on my computer, but south of two. Given fewer advantages, I would go with the approximations that would have fall simply be a day, one of 360, good enough for naked-eye, but now that I've got the tools, and I want to use them.
The response that has stuck out in this thread is the one from haukex, and I'm still writing up the results in a way that might befit my future friar status as well as the keystroke equity he put into a response that catered to my exact level of aptitude. Let's however, finish with the original script.
Given right ascension, a naive model has half of it before solar noon, and half after. Finally, we divide by 15 for dimensional analysis. The greeks really did use the sun like a watch.
With the original script, there is no surprises. It doesn't matter where you are on Earth at the onset of autumn, delta will equal zero. So for everyone except 2 simple poles, you will have 12 hour days:
C:\Users\Fred\Desktop>perl fall2.pl cos tau = - tan phi * tan delta onset of fall ==> delta equal zero delta is 0 delta equals zero will zero out rhs for entire globe phi is latitude: 45 in portland (close enough) phi is 0.785398163397448 rhs is 0 tau is 1.5707963267949 degrees is 90 estimate is 12 agrees with theory given mathematical objects with primitive assumptio +ns C:\Users\Fred\Desktop>type fall2.pl #!/usr/bin/perl -w use strict; use 5.010; use Math::Trig; use Math::Trig ':pi'; say "cos tau = - tan phi * tan delta"; say "onset of fall ==> delta equal zero"; my $delta = tan( 0); say "delta is $delta"; say "delta equals zero will zero out rhs for entire globe"; say "phi is latitude: 45 in portland (close enough)"; my $phi = deg2rad(45); say "phi is $phi"; my $rhs = - tan ($phi) * tan ($delta); say "rhs is $rhs"; my $tau = acos($rhs); say "tau is $tau"; my $degrees = rad2deg($tau); say "degrees is $degrees"; my $estimate = 2 * $degrees/15; say "estimate is $estimate"; say "agrees with theory given mathematical
There's *a lot* of reading, but the good news is that we stand on the shoulders of people who make compilers hum for an hour. Much of the work seemed to be the product of a D. Rolsky. I show none of his work in this, so maybe that's a teaser for downthread. Having witnessed the US presidential debate tonight, my ability to use words larger than a 12 year old might be impaired. Das wird ebenfalls passierien.
Schoenen Gruss
In reply to Re^3: calculate length of day as function of space at onset of fall
by Aldebaran
in thread calculate length of day as function of space at onset of fall
by Aldebaran
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