H-R Diagram Gizmo : Lesson Info : ExploreLearning H-R Diagram. Launch Gizmo. Good activity for building understanding of HR diagram and how we classify stars. Recommended for: Earth/Space Science, Physics Access to ALL Gizmo lesson materials, including answer keys. Customizable versions of all lesson materials. H-R Diagram Gizmo : ExploreLearning H-R Diagram. Lesson Info . Create New Preset How do Presets Work? Cancel. Save. Access to ALL Gizmo lesson materials, including answer keys. If you are a teacher, please provide us with the 8-digit Registration Key provided by your Gizmos administrator.