C Library Functions  - phase_of_moon (3)

NAME
phase_of_moon(3f) - [M_time:ASTROLOGICAL] return name for phase of moon for given date (LICENSE:MIT)

CONTENTS

Synopsis
Description
Examples
Author
License

SYNOPSIS
function phase_of_moon(dat) 

   integer,intent(in)            :: dat(8)
   character(len=:),allocatable  :: phase_of_moon

DESCRIPTION
Phases Of The Moon

This procedure is used to support the %p field descriptor for the fmtdate(3f) routine.

The moon circles the earth every 29.530588853 days on average, so pick a starting point and count. A new moon occurred at Julian date 2451550.1 (January 6, 2000, 18:14 UTC). Then it is easy to count the number of days since the last new moon. This is an approximate calculation.

There are eight generally recognized phases of the moon in common use

o new or dark
o waxing crescent
o first quarter
o waxing gibbous
o full
o waning gibbous
o last quarter
o waning crescent

To calculate the phase of the moon simply divide the days since the last new moon by eight and select the appropriate phase.

Note that technically the four states (new, first quarter, full, third quarter) are events not phases. That is to say, the moon is technically only new for an instant.

EXAMPLES
Sample: 

  program demo_phase_of_moon
  use M_time, only : now
  use M_time, only : phase_of_moon
  use M_time, only : moon_fullness
  implicit none
  integer :: dat(8)
   ! generate DAT array
   call date_and_time(values=dat)
   ! show DAT array
   write(*,’(" Today is:",*(i0:,":"))’)dat
   ! the %p and %P fields are supported by fmtdate(3f)
   write(*,*)&
   & now(’The phase of the moon is %p, with a fullness of %P’)
   write(*,’(1x,*(a))’,advance=’no’)&
   & ’The phase of the moon is ’,trim( phase_of_moon(dat)),’,’
   write(*,’(1x,a,i0,a)’)’with a fullness of ’,moon_fullness(dat),’%’
  end program demo_phase_of_moon
Sample output: 

    Today is:2018:11:3:-240:20:18:44:245
    The phase of the moon is Waning crescent, with a fullness of -30%
    The phase of the moon is Waning crescent, with a fullness of -30%

AUTHOR
John S. Urban, 2015

LICENSE

    MIT

Nemo Release 3.1 phase_of_moon (3) February 23, 2025
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