07_moon_properties.cpp

Moon phase properties and illumination-window searches.

// SPDX-License-Identifier: AGPL-3.0-or-later
// Copyright (C) 2026 Vallés Puig, Ramon
 
 
#include <siderust/siderust.hpp>
 
#include <iomanip>
#include <iostream>
#include <string>
#include <vector>
 
using namespace siderust;
using namespace qtty::literals;
 
template <typename T> static CivilTime to_utc_civil(const T &time) {
  return time.template to<scale::UTC>().to_civil();
}
 
void print_periods(const std::string &label, const std::vector<Period<TT, MJD>> &periods) {
  std::cout << "\n" << label << ": " << periods.size() << " period(s)" << std::endl;
  for (const auto &p : periods) {
    auto dur_h = p.duration<qtty::Hour>();
    auto s = to_utc_civil(p.start());
    auto e = to_utc_civil(p.end());
    std::cout << "  - " << s << " -> " << e << " (" << dur_h << ")" << std::endl;
  }
}
 
int main() {
  // Default site: Roque de los Muchachos
  double lat = 28.762;
  double lon = -17.892;
  double h_m = 2396.0;
 
  Geodetic site{qtty::Degree(lon), qtty::Degree(lat), qtty::Meter(h_m)};
 
  // Use a fixed date for reproducibility: 2026-03-01 00:00 UTC
  auto jd = Time<TT, JD>::from_utc({2026, 3, 1, 0, 0, 0});
  auto mjd = jd.to<format::MJD>();
  auto window = Period<TT, MJD>(mjd, mjd + qtty::Day(35.0));
  SearchOptions opts{};
 
  // =========================================================================
  // 1) Point-in-time phase properties
  // =========================================================================
  auto geo = moon::phase_geocentric(jd);
  auto topo = moon::phase_topocentric(jd, site);
 
  std::cout << std::fixed;
  std::cout << "Moon phase at 2026-03-01 00:00 UTC" << std::endl;
  std::cout << "==================================" << std::endl;
  std::cout << std::setprecision(4);
  std::cout << "Site: lat=" << lat << " deg, lon=" << lon << " deg, h=" << std::setprecision(0)
            << h_m << " m" << std::endl;
 
  std::cout << "\nGeocentric:" << std::endl;
  std::cout << "  label                 : " << moon::phase_label(geo) << std::endl;
  std::cout << std::setprecision(4);
  std::cout << "  illuminated fraction  : " << geo.illuminated_fraction << std::endl;
  std::cout << std::setprecision(2);
  std::cout << "  illuminated percent   : " << illuminated_percent(geo) << " %" << std::endl;
  std::cout << "  phase angle           : " << geo.phase_angle.to<qtty::Degree>() << std::endl;
  std::cout << "  elongation            : " << geo.elongation.to<qtty::Degree>() << std::endl;
  std::cout << "  waxing                : " << std::boolalpha << geo.waxing << std::endl;
 
  std::cout << "\nTopocentric:" << std::endl;
  std::cout << "  label                 : " << moon::phase_label(topo) << std::endl;
  std::cout << std::setprecision(4);
  std::cout << "  illuminated fraction  : " << topo.illuminated_fraction << std::endl;
  std::cout << "  illumination delta    : " << std::showpos
            << (topo.illuminated_fraction - geo.illuminated_fraction) * 100.0 << std::noshowpos
            << " %" << std::endl;
  std::cout << "  elongation            : " << topo.elongation.to<qtty::Degree>() << std::endl;
 
  // =========================================================================
  // 2) Principal phase events
  // =========================================================================
  auto events = moon::find_phase_events(window, opts);
  std::cout << "\nPrincipal phase events in next 35 days: " << events.size() << std::endl;
  for (const auto &ev : events) {
    auto utc = to_utc_civil(ev.time);
    std::cout << "  - " << std::setw(13) << std::right << ev.kind << " at " << utc << " UTC"
              << std::endl;
  }
 
  // =========================================================================
  // 3) Illumination range searches
  // =========================================================================
  auto crescent = moon::illumination_range(window, 0.05, 0.35, opts);
  auto quarterish = moon::illumination_range(window, 0.45, 0.55, opts);
  auto gibbous = moon::illumination_range(window, 0.65, 0.95, opts);
 
  print_periods("Crescent-like range (5%-35%)", crescent);
  print_periods("Quarter-like range (45%-55%)", quarterish);
  print_periods("Gibbous-like range (65%-95%)", gibbous);
 
  return 0;
}