One day in the early 17th century, Hans Lippershey, the owner of an optical shop in a small Dutch town, lined up a convex lens and a concave lens in order to check the quality of the ground lenses. Looking through the lens, I found that the church spire in the distance seemed to be getting bigger and closer, so I accidentally discovered the secret of the telescope. In 1608, he applied for a patent for the telescope he made and complied with the authorities' request to build a pair of binoculars. It is said that dozens of opticians in the town claimed to have invented the telescope, but Liebersch is generally believed to be the inventor of the telescope.
News of the invention of the telescope quickly spread throughout Europe. After learning about the news, Italian scientist Galileo Galilei made his own one. The first telescopes could only magnify objects 3 times. A month later, the second telescope he built could magnify 8 times, and the third telescope could magnify 20 times. In October 1609, he built a telescope that could magnify 30 times. Galileo used a homemade telescope to observe the night sky and discovered for the first time that the moon's surface was rugged, covered with mountains and had cracks in craters. After that, he discovered the four satellites of Jupiter and the sunspot movement of the sun, and concluded that the sun is rotating.
Almost at the same time, the German astronomer Kepler also began to study telescopes. He proposed another astronomical telescope in "Diopters". This telescope consisted of two convex lenses, which was different from Galileo's telescope. , with a wider field of view than the Galilean telescope. But Kepler did not build the telescope he described. Scheiner first made this kind of telescope between 1613 and 1617. He also followed Kepler's suggestion and made a telescope with a third convex lens, turning the inverted image of the telescope made of two convex lenses into an upright image. . Scheiner built 8 telescopes and observed the sun one by one. No matter which one, he could see the same shape of sunspots. Therefore, he dispelled many people's illusion that sunspots may be caused by dust on the lens, and proved that sunspots are indeed observed. Scheiner installed special light-shielding glass when observing the sun, but Galileo did not add this protective device. As a result, he injured his eyes and was almost blind in the end. In order to reduce the chromatic aberration of the refracting telescope, Huygens of the Netherlands built a telescope with a barrel length of nearly 6 meters in 1665 to explore the rings of Saturn, and later built a telescope with a length of nearly 41 meters.