The Milky Way galaxy is the galaxy we live in. The Milky Way galaxy contains over 10 billion stars like the Sun. All these stars are very far from us compared to the Sun which is only 93 million miles away. So no space probe has left the Milky Way galaxy or even come close. Astronomers treat this like a puzzle.
Lets consider the Earth first.
Ancient Babylonians knew the Earth was a sphere 5,000 years before the first satellite pictures of the Earth from space. You might attempt the same kind of puzzle. The next step was to examine the position of very luminous objects called globular clusters. They mapped the position of the clusters and found that most of the clusters are located to one side of the Sun indicating that we are not at the center of the disk. White light is a combination of all the different colors.