Alex and Alice went on a trip to the countryside. The day is wonderful, the sky is blue, and the sunlight warms the earth. The two children gaze at the sky and wonder how many people have raised their eyes with the same curiosity. What could be up there that the eye cannot reach? After all, through observation, humans discovered our solar system and the universe. Fortunately for them, their mom is an astrophysicist and can explain many things about the sky that they had never imagined.