diff --git a/README b/README
index 29bfc89..82efca5 100644
--- a/README
+++ b/README
@@ -29,3 +29,5 @@ Then to build run standard cmake sequence
 For working plate solving you must have compiled and installed StellarSolver https://github.com/rlancaste/stellarsolver
 It is important that you compile StellarSolver with Qt6. By default it use Qt5 but when linked with Qt6 program it will
 crash.
+
+Using OpenNGC database https://github.com/mattiaverga/OpenNGC under [CC-BY-SA-4.0](https://creativecommons.org/licenses/by-sa/4.0/)