I shall present a series of easy demonstrations that can be carried out during formal astronomy lectures. Since astronomy is physics we have developed on Earth applied to celestial objects, there are many useful experiments that can be carried out with relative ease by physics teachers in order to help pupils grasp the workings of the universe and to relate them with every day experiences. One of the difficulties in teaching science is that we use two-dimensional pictures to explain a three-dimensional reality. Using models helps students understand some of the properties of celestial objects. Although it is important to have pupils experiment on their own, some demonstrations are so simple that it is enough to have the teacher carry them out during the lecture to have pupils grasp their importance or at least keep their attention focused on the topic at hand. The demonstrations can be used in elementary education as well as in introductory astronomy courses and teacher workshops.