Because we are inside of it.
by eyes
The Milky Way Galaxy.
We (the carbon units who inhabit the Earth) have named our galaxy the "Milky Way". If there's anybody else out there, we have no idea what they call our galaxy, or whether they care.
The Milky Way was named when the early astronomers looked up at the night sky and saw a milky band of dim stars going across the sky.
Most of the observation astronomers make are inside our Galaxy. Of course we still find new things. The Milky Way is a very complex and diverse collection of celestial objects. We still have much to learn!
They don't. That's the job of astronomers.
No one knows the answer to that because astronomers haven't been able to explore any other galaxies besides the Milky Way.
Astronomers study the Andromeda galaxy to learn more about how galaxies form and evolve, to understand the structure and composition of other galaxies beyond our own Milky Way, and to potentially gain insights into the future fate of our own galaxy.
Astronomers suspect that a super massive black hole is at the center of the Milky Way. Over a period of several years, astronomers have observed that stars near the center of the Milky Way are orbiting an object with massive gravitation, and the object emits no light. What can it be? A black hole is the best answer, and by the way the stars move, it must a super massive one.
The realization that the Milky Way is a disk of stars was largely attributed to the work of astronomers in the 18th century, particularly Immanuel Kant. He proposed that the Milky Way was a vast collection of stars, which later observations by astronomers like William Herschel in the late 1700s provided further evidence for. Herschel's star counts and mapping of the Milky Way's structure helped reinforce the understanding of its disk-like shape.
Astronomers have calculated that it takes the Sun 226 million years to completely orbit around the center of the Milky Way.
The Milky Way, included every object in space