feature(helioviewer): add documentation about sources to the script and update the readme

helioviewer_grab.py

@@ -6,6 +6,7 @@ Holt ein Sonnen-Vollscheibenbild von Helioviewer zu einem Zeitpunkt.
 Beispiel:
     ./helioviewer_grab.py 2026-08-12T18:18:00Z hmi_continuum
     ./helioviewer_grab.py --list
+    ./helioviewer_grab.py --sources
 """
 
 import json
@@ -15,6 +16,26 @@ import urllib.request
 
 API = "https://api.helioviewer.org/v2"
 
+# Kuratierte Kurzerklaerung der gebraeuchlichsten Quellen (sourceId -> Text).
+# Nur eine Auswahl, keine vollstaendige Doku -- fuer alle IDs siehe --list.
+SOURCE_INFO = {
+    8: "AIA 94 - hot flare plasma (~6 MK)",
+    9: "AIA 131 - flaring regions (~10 MK)",
+    10: "AIA 171 - quiet corona, coronal loops (~0.8 MK)",
+    11: "AIA 193 - corona, coronal holes (~1.2 MK)",
+    12: "AIA 211 - active region corona (~2 MK)",
+    13: "AIA 304 - chromosphere/transition region, prominences (~0.05 MK)",
+    14: "AIA 335 - active region corona (~2.5 MK)",
+    15: "AIA 1600 - upper photosphere/transition region, flare ribbons",
+    16: "AIA 1700 - photosphere/temperature minimum",
+    17: "AIA 4500 - near-visible continuum, sunspots",
+    18: "HMI continuum - white-light photosphere: sunspots, granulation "
+        "(highest full-disk resolution, 0.5\"/px)",
+    19: "HMI magnetogram - photospheric magnetic field map",
+    94: "GONG H-alpha - chromosphere: filaments, plage, flare ribbons "
+        "(ground-based network)",
+}
+
 
 def call(endpoint, **params):
     """GET auf die Helioviewer-API. Gibt (content_type, bytes) zurueck."""
@@ -64,6 +85,11 @@ def main():
             print(f"{sid:4d}  {'/'.join(path):40s}  {nick}")
         return
 
+    if "--sources" in sys.argv:
+        for sid, desc in sorted(SOURCE_INFO.items()):
+            print(f"{sid:4d}  {desc}")
+        return
+
     date = sys.argv[1] if len(sys.argv) > 1 else "2026-08-12T18:18:00Z"
     what = sys.argv[2] if len(sys.argv) > 2 else "continuum"