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doc/astronomical-notes.pod  view on Meta::CPAN

speed. In the end, it is better than the basic algorithm, which uses an approximate
but still wrong orbital speed, but for the whole span of 3 h, 59 mn and 57 s.

=head2 What Happened in Spring 2020?

Let us look a bit farther into  the past. In January 2019, I published
version  0.98   of  L<Astro::Sunrise>,  with  the   precise  algorithm
implemented as explained in the  preceding paragraph. For test data, I
did not know how to cross-check  with authoritative sources, so I just
checked  they  looked plausible  and  that  the iterative  computation
stopped after  a few iterations. At  this time, I did  not synchronise
L<DateTime::Event::Sunrise> with L<Astro::Sunrise>, because it was not
the proper time yet.

Then in  April 2020, a user  created an RT ticket,  explaining that he
had   compared  the   results   of  L<DateTime::Event::Sunrise>   with
authoritative websites and  that the results were  not precise enough.
Of course  the results were  not precise,  I had not  yet synchronised
L<DateTime::Event::Sunrise>  with L<Astro::Sunrise>.  Yet this  ticket
gave  me two  things: first,  a  website which  would provide  precise
day-after-day computations of sunrise, sunset and real solar noon, and

lib/Astro/Sunrise.pm  view on Meta::CPAN

what I have tried to accomplish with this.

a) Compute sunrise or sunset as always, with one exception: to convert LHA from degrees to hours,
   divide by 15.04107 instead of 15.0 (this accounts for the difference between the solar day
   and the sidereal day).

b) Re-do the computation but compute the Sun's RA and Decl, and also GMST0, for the moment
   of sunrise or sunset last computed.

c) Iterate b) until the computed sunrise or sunset no longer changes significantly.
   Usually 2 iterations are enough, in rare cases 3 or 4 iterations may be needed.

This parameter is optional. It can be positional (#9).

=back

=head3 I<For Example>

 ($sunrise, $sunset) = sunrise( 2001, 3, 10, 17.384, 98.625, -5, 0 );
 ($sunrise, $sunset) = sunrise( 2002, 10, 14, -105.181, 41.324, -7, 1, -18);
 ($sunrise, $sunset) = sunrise( 2002, 10, 14, -105.181, 41.324, -7, 1, -18, 1);