If someone asked you what the Milky Way looked like, you would definitely answer that it was a flattened barred spiral galaxy with a diameter of about 160,000 light-years, because that's what we see in our usual maps.
But are you confused by the question of how do we know what the Milky Way looks like before we even fly out of the solar system? As the saying goes, I don't know the true face of Lushan, only because I am in this mountain.
In fact, all the maps we see about the Milky Way are not the real Milky Way, but the observation and simulation of scientists. Since we are in the Milky Way, it is impossible to see the full picture of the Milky Way unless we leave the galaxy and go to a more distant location, but the Milky Way is so vast that even a trip at the speed of light of 300,000 kilometers per second would take 160,000 light-years, which is simply impossible for human beings to achieve with current technology.
We know that if you are standing in an open space and want to draw a panoramic view of your location, you can get a rough picture of your area by taking a rough measurement of the location and distance of the surrounding things (e.g., trees, houses, and stones).
Therefore, if we want to know the whole picture of the Milky Way, scientists need to observe a large number of other stars in the Milky Way, and then measure the distance and position of these celestial bodies from the Earth.
By looking at the distance, position, and speed of other stars, we can not only know the general structure of the Milky Way, but also infer where we are in the Milky Way and how it moves.
According to current observations, our Milky Way is a barred spiral galaxy with an elliptical disk structure and four clear cantilevers, while our solar system is located at the edge of the Milky Way, in a cantilever called Orion, about 260,000 light years. At this time, we are revolving around the heart of the silver at a speed of 230 kilometers per second, and we can move 1500 million kilometers, 1400 years moving a light year, 2500 million years can circle the center of the Milky Way.
In 2015, scientists found that our Milky Way is more than 50 percent larger than previously thought, so the diameter of the Milky Way has been revised from about 100,000 light-years to 16-180,000 light-years.