diff --git a/cmd/sun/main.go b/cmd/sun/main.go
index bf78d93..db67a07 100644
--- a/cmd/sun/main.go
+++ b/cmd/sun/main.go
@@ -13,9 +13,13 @@ import (
 
 var (
 	coordinates = flag.String("c", "", "coordinates")
-	date        = flag.String("d", "", "date in YYYY-MM-DD format")
-	tz          = flag.String("z", "", "timezone")
-	f           = flag.String("f", "", "output time format")
+	date        = flag.String(
+		"d", "", "date in YYYY-MM-DD format (default: today)",
+	)
+	tz = flag.String("z", "", "timezone (default: UTC)")
+	f  = flag.String(
+		"f", "", "output time format (default: RFC 3339)",
+	)
 )
 
 func main() {