How do astronomers gain confidence in the inferred structure of our galaxy?

By studying and comparing measurements to external barred spiral galaxies.

Since obtaining an external vantage point to photograph the Milky Way is impossible, astronomers rely significantly on comparative modeling. They study hundreds of other galaxies that can be viewed face-on or edge-on, particularly those identified as barred spirals (like NGC 1300 or M83). If the detailed internal measurements gathered from the Milky Way—including stellar motion data, gas distribution patterns detected via radio astronomy, and the location of dust lanes identified through infrared—match the expected characteristics of these external barred spirals, it serves as strong confirmation of our inferred structure. This external validation process provides the necessary confidence beyond what internal measurements alone can offer.