diff --git a/Makefile b/Makefile
index 6a3f7f7..6c2d06c 100644
--- a/Makefile
+++ b/Makefile
@@ -42,9 +42,12 @@ LDFLAGS := -lSDL2 -lGLEW -lGL
 endif
 
 
-all: mkdirs $(BIN) $(TEST_BIN)
+all: mkdirs $(BIN)
 .PHONY: all
 
+tests: $(TEST_BIN)
+.PHONY: tests
+
 -include $(OBJDIR)/*.d
 
 mkdirs:
@@ -77,7 +80,6 @@ $(LIB):
 	USE_INTERNAL_ASSIMP=$(USE_INTERNAL_ASSIMP) $(MAKE) -C $(LIBDIR)
 
 clean:
-	rm -rf $(OBJDIR)/* $(BIN) bin/test_orbit
-	$(MAKE) -C $(LIBDIR) clean
+	@rm -rf $(BIN) $(TEST_BIN) $(COMMON_OBJECTS) $(OBJECTS) $(TEST_OBJECTS)
 .PHONY: clean
 
diff --git a/ext/tangerine b/ext/tangerine
index ca151b5..9e549fc 160000
--- a/ext/tangerine
+++ b/ext/tangerine
@@ -1 +1 @@
-Subproject commit ca151b5c770eb586c697fe3d29c49f0de3450e1e
+Subproject commit 9e549fcb8817de4199479674418a8c86528a7d9e
diff --git a/src/orbits.h b/src/orbits.h
index 112e2d5..eee3503 100644
--- a/src/orbits.h
+++ b/src/orbits.h
@@ -15,8 +15,8 @@ struct ellipse_parameters
 	double e;	// NOTE: eccentricity
 	double c;	// NOTE: linear eccentricity
 	double p;	// NOTE: semilatus rectum
-	glm::vec2 f1;
-	glm::vec2 f2;
+	glm::vec2 f1;	// NOTE: 'vacant' focus
+	glm::vec2 f2;	// NOTE: 'primary' focus
 };
 
 struct orbital_elements