// A program to disprove the e-mail that says,
// "February 1865 is the only month in recorded history not to have a full
// moon."

// For a month to have no full moon, the illuminated fraction has to be
// decreasing at the beginning of the month and increasing at the end of
// the month.  This will only work in February because a lunar month is
// 29.5305555 days.

use sun.frink

timezone = "UTC"

// Start with the first February after the Gregorian calendar was adopted
// (which was October 15, 1582)
for year = 1583 to 2020
{
   start = parseDate["$year-02-01 00:00 $timezone"]
   end = parseDate["$year-03-01 00:00 $timezone"]

   if moonIlluminatedFraction[start] > moonIlluminatedFraction[start + 1 s] and moonIlluminatedFraction[end - 1 s] < moonIlluminatedFraction[end]
      print["$year "]
}

println[]

// Find the actual date of the full moon in February 1865.
fullMoon1865 = fullMoon[#February 1, 1865#]
println["A full moon actually occurred that month on $fullMoon1865"]