What evidence shows the Milky Way is a spiral galaxy and where we are in it?
Robert Sungenis answers that astronomers are making educated guesses rather than observing it directly, since no probe can photograph the Milky Way from outside. He notes that the assumption rests on the visible band of stars and on Andromeda being a spiral, and adds that galaxies spin roughly ten times too fast for present physical laws.
A viewer asks what evidence is used to claim the Milky Way is a spiral galaxy and to locate our position within it.
Answer
They do not really know; they are making educated guesses, because there are no cameras out there taking pictures of the Milky Way, and we cannot even get a probe reliably past Pluto. We assume it is a spiral because on a clear night you can see a thin band of stars across the sky, which is usually a sign of a spiral galaxy, and because our nearest galaxy, Andromeda, which we can photograph from the outside, is clearly a spiral. Seeing that band, and that there are stars behind us as well, they estimate we are about two-thirds out from the center on one of the arms. By the way, these galaxies are spinning about ten times too fast for our present physical laws, which is a problem modern science does not like to discuss.