Update app.py

app.py

@@ -77,24 +77,37 @@ def PLadder_ZSizes(utc_dt, lat, lon):
     """Calculate Planetary Ladder and Zone Sizes."""
     if not 1900 <= utc_dt.year <= 2050:
         return {"error": "Date out of range (1900–2050)."}
+
+    # Load the JPL ephemeris (DE421)
     planets = load('de421.bsp')
     earth = planets['earth']
-    observer = earth + Topos(latitude_degrees=lat, longitude_degrees=lon)
+    
+    # Define planet objects (using barycenters for Jupiter and Saturn)
     planet_objects = {
         'Sun': planets['sun'], 'Moon': planets['moon'], 'Mercury': planets['mercury'],
         'Venus': planets['venus'], 'Mars': planets['mars'], 
         'Jupiter': planets['jupiter barycenter'], 'Saturn': planets['saturn barycenter']
     }
+    
+    # Create a timescale and convert the UTC datetime to a Skyfield time object
     ts = load.timescale()
     t = ts.from_datetime(utc_dt)
+
+    # Calculate geocentric ecliptic longitudes for each planet
     longitudes = {}
     for planet, obj in planet_objects.items():
-        astrometric = observer.at(t).observe(obj)
-        _, lon, _ = astrometric.apparent().ecliptic_latlon()
-        longitudes[planet] = lon.degrees
+            # Geocentric position from Earth's center
+            astrometric = earth.at(t).observe(obj)
+            apparent = astrometric.apparent()
+            _, lon, _ = apparent.ecliptic_latlon()
+            longitudes[planet] = lon.degrees
+
+    # Sort planets by their ecliptic longitude
     sorted_planets = sorted(longitudes.items(), key=lambda x: x[1])
     PLadder = [p for p, _ in sorted_planets]
     sorted_lons = [lon for _, lon in sorted_planets]
+
+    # Calculate zone sizes (angular distances between consecutive planets)
     zone_sizes = [sorted_lons[0]] + [sorted_lons[i+1] - sorted_lons[i] for i in range(6)] + [360 - sorted_lons[6]]
     bordering = [[PLadder[0]]] + [[PLadder[i-1], PLadder[i]] for i in range(1, 7)] + [[PLadder[6]]]
     ZSizes = []