As early as the 5th and 6th century BC, the Greek philosopher Pythagoras put forward the idea that the earth is spherical, and Aristotle inferred that the earth is round according to the circular shadow on the surface of the moon during the eclipse. This is the first time that mankind has explored the shape of the earth from a scientific point of view. After long-term observation and calculation,16th century Dutch astronomer Copernicus.

The famous Heliocentrism was put forward, paving the way for people to understand the earth. Later, Galileo, Kepler, Newton and other scientists continued to explore, especially after the 1960s, with the rapid development of science and technology and the launch of satellites, they found new methods for geodesy. People already know that the earth is an extremely ordinary star in the vast universe-one of the nine planets in the solar system. In addition, geographical discovery is an important reason!

Since ancient times, people have a deep obsession with "flying", and "heaven" is what we call the universe. Since the invention of observation tools in17th century, human beings have been interested in galaxies in the depths of the universe. There are many galaxies in the universe, and people call all galaxies outside the Milky Way galaxy extrasolar galaxies. So, who first discovered it, and how did you prove that it was outside the Milky Way?

There is still a long way to go in the study of galaxies. There are too many problems about the universe and galaxies. There are too many questions, too many curiosity. All these require people to explore more and solve more mysteries. Exploration to the present is a small step in the exploration of the universe, a part of astronomy and the most important part, constantly denying the past and constantly overthrowing old knowledge. Yesterday's "no"