NAME

Astro::Montenbruck::RiseSet::RST — rise, set, transit.

SYNOPSIS

    use Astro::Montenbruck::MathUtils qw/frac/;
    use Astro::Montenbruck::RiseSet::Constants qw/:events :altitudes/;
    use Astro::Montenbruck::RiseSet::RST qw/rst_function/;

    # create function for calculating Moon events for Munich, Germany, on March 23, 1989.
    my $func = rst_function(
        date     => [1989, 3, 23],
        phi    => 48.1,
        lambda => -11.6,
        get_position => sub {
            my $jd = shift;
            # return equatorial coordinates of the celestial body for the Julian Day.
        }
    );

    # calculate rise. Alternatively, use $EVT_SET for set, $EVT_TRANSIT for
    # transit as the first argument
    $func->(
        $EVT_RISE,
        on_event  => sub {
            my $jd = shift; # Standard Julian date of the event
            my $ut = frac(jd - 0.5) * 24; # UTC, 18.95 = 18h57m
        },
        on_noevent => sub {
            my $state = shift;
            say "The body is $state"
        }
    });

VERSION

Version 0.01

DESCRIPTION

Low-level routines for calculating rise, set and transit times of celestial bodies. The calculations are based on "Astronomical Algorythms" by Jean Meeus. The same subject is discussed in Montenbruck & Phleger's book, but Meeus's method is more general and consistent. Unit tests use examples from the both sources.

The general problem here is to find the instant of time at which a celestial body reaches a predetermined altitude.

FUNCTIONS

rst_function( %args )

Returns function for calculating time of event. See "EVENT FUNCTION" below.

Named Arguments

• date — array of year (astronomical, zero-based), month [1..12], and day, [1..31].

• phi — geographical latitude, degrees, positive northward

• lambda — geographical longitude, degrees, positive westward

• get_position — function, which given Standard Julian Day, returns equatorial coordinates of the celestial body, in radians.

• h — the standard altitude, i.e. the geometric altitude of the center of the body at the time of apparent rising or setting, degrees.

EVENT FUNCTION

The event function, returned by "rst_function( %args )", calculates time of a given event (rise, set or trasnsit).

    $func->( EVENT_TYPE, on_event => sub{ ... }, on_noevent => sub{ ... } );

Its first argument, event type, is one of $EVT_RISE, $EVT_SET, or $EVT_TRANSIT, see "EVENTS" in Astro::Montenbruck::RiseSet::Constants.

Named arguments are callback functions:

• on_event is called when the event time is determined. The argument is Standard Julian day of the event.

      on_event => sub { my $jd = shift; ... }

• on_noevent is called when the event does not happen at the given date, either because the body never rises, or is circumpolar. The argument is respectively $STATE_NEVER_RISES or $STATE_CIRCUMPOLAR, see "STATES" in Astro::Montenbruck::RiseSet::Constants.

      on_noevent => sub { my $state = shift; ... }

AUTHOR

Sergey Krushinsky, <krushi at cpan.org>

COPYRIGHT AND LICENSE

Copyright (C) 2010-2021 by Sergey Krushinsky

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.