/** This program tries to date Galileo's notebooks about the moons of Jupiter.

    See :
   https://mobile.twitter.com/brettmor/status/1634214929933783043/photo/1

   Which happened around 1610.  

   The first test is to find when all the moons of Jupiter are on the same side
   of the planet.  This means the signums of their x-values are the same.
*/

use planets.frink

signumsOfX = {|m| signum[m@0]}

lat = 45 degrees North
long = 11 degrees East

for d = #1610-01-01# to #1620-01-01# step 1 hours
{
   // Now make sure the sun is below the horizon
   [azsun, altsun] = refractedSunAzimuthAltitude[d, lat, long]
   if altsun < 0 degrees
   {
      // Test when all the moons of Jupiter are on the same side of the planet
      // (x-values all have the same signum.)
      m = Planet.JupiterMoonsPosition[d]
      signums = map[signumsOfX, m]
      if (allSame[signums])
      {
         // Next make sure that Jupiter is above the horizon
         [az, alt] =  Planet.Jupiter.refractedAzimuthAltitude[d, lat, long]

         if alt > 0 degrees
            println[d -> Italy]
      }
   }
}