Telescope is an optical instrument that uses optical devices such as lenses or mirrors to observe distant objects. The light passing through the lens is refracted or reflected by concave mirror into the pinhole to converge and image, and then it is seen through the magnifying eyepiece. Also known as "a thousand-mile mirror". The first function of the telescope is to enlarge the opening angle of distant objects, so that the human eye can see the details with smaller angular distance. The second function of the telescope is to send the light beam collected by the objective lens, which is much thicker than the pupil diameter (up to 8 mm), to the human eye, so that the observer can see dim objects that he could not see before. 1608, Hans Justus Hans Liebig, a Dutch optician, accidentally discovered that two lenses could be used to see the distant scenery. Inspired by this, he made the first telescope in human history. After nearly 400 years of development, the function of the telescope is becoming more and more powerful, and the observation distance is getting farther and farther. 1609 Italian Florentine Galileo Galili Lei Faming made a 40x telescope, which is the first practical telescope put into scientific application.