diff --git a/modules/util/util.py b/modules/util/util.py
index 30b6d0ce2b7ae6bf037cc740d79f91bb7a14e7c9..c132ebc66ca1a4f2c0db05bdcdf1434a047f3ba3 100644
--- a/modules/util/util.py
+++ b/modules/util/util.py
@@ -150,4 +150,14 @@ def minimize_quadratic(xa, xb, xc, ya, yb, yc):
 def value_to_index(nda, value):
     diff = np.abs(nda - value)
     idx = np.argmin(diff)
-    return idx
\ No newline at end of file
+    return idx
+
+
+# array solzen must be degrees, missing values must NaN
+def is_night(solzen, threshold):
+    solzen = solzen.flatten()
+    solzen = solzen[np.invert(np.isnan(solzen))]
+    if np.max(solzen) > threshold:
+        return True
+    else:
+        return False