If the Sun is shining, it continuously sends Solar Energy to the Earth, in the form of Photon messages.
This is a Rose RealTime behavior diagram. These diagrams are drawn by software designers to specify the behavior of an entity, in this case the Sun, at run-time. The Sun entity is implemented with two states. It’s either Shining or it’s Dead. If it’s shining, then it periodically times out, as shown in the diagram by the timeout transition (line), and executes the C++ code - SolarEnergy.send(Photon); .