A telescope is an optical instrument that uses lenses or mirrors and other optics to observe distant objects. It uses the refraction of light through the lens or the light reflected by the concave mirror to enter the small hole and converge for imaging, and then pass through a magnifying eyepiece to be seen, also known as "clairvoyant".
The first function of the telescope is to magnify the opening angle of distant objects, so that the human eye can see details with smaller angular distances. The second function of the telescope is to send a beam much thicker than the diameter of the pupil (up to 8 mm) collected by the objective lens into the human eye, so that the observer can see faint objects that were previously invisible.
In 1608, Hans Liebersch, an optician in the Netherlands, stumbled upon a two-lens that could see distant objects clearly, and he was inspired to build the first telescope in human history. In 1609, the Italian Florentine Galileo Galilei invented the 40x double-mirror telescope, which was the first practical telescope put into scientific use. After more than 400 years of development, the telescope has become more and more powerful, and the observation distance has become farther and farther.