Abstract
Textbooks used in elementary and junior high schools must be written based on the Courses of Study in Japan. Science textbooks show observation of the moon and the sun using a small astronomical telescope. However, most in-service teachers have never used an astronomical telescope. Teachers have to use it safely to secure the safety of pupils, students, and teachers. I examined wrong and unsafe acts while in-service teachers and students assembled astronomical telescopes. Then I developed digital teaching materials for teachers including risks caused by wrong acts
