While boxing up books to make room for more books on my shelves* I came across my paternal grandmother's astronomy textbook from when she was a student at Campbell-Hagerman College**.
I hadn't looked at it in years and glancing through it today I was struck again by how much our knowledge of the universe increased over the 20th Century and a bit of the 21st. In fact, in the 1904 text the only time the word "universe" is mentioned, and then briefly, is as the "stellar universe". In other words, our Milky Way galaxy was thought to be the universe.
Even our galaxy was a mystery. "As to the Milky Way itself, it is not certain whether the stars which compose it form a sort of thin, flat, continuous sheet, or whether they are arranged in a sort of ring with a comparatively empty space in the middle, where the sun is situated, not far from the center." The thin, flat, continuous sheet theory came close but now we know our star and planets reside somewhere close to the edge, not the near the center.
Astronomers in 1904 had very good telescopes and took photos of other galaxies. The problem was that they didn't know what they were looking at. Everything that wasn't a star was a "nebula" (from Latin for "cloud.") They knew the difference between the gaseous nebulae like the one in Orion's belt and the "long oval with dark lanes in it, and a bright nucleus much like a star" that turned out to be the Andromeda galaxy. But they thought both existed within the Milky Way. It wasn't until 1925 that Edwin Hubble determined that the Andromeda nebula was, in fact, a separate galaxy and a significant distance away from the our Milkly Way galaxy.
*For giggles I mesured my bookshelves. If they were one long book shelf it would be 82' long. Not nearly enough. I'd buy more bookshelves but I have no place to put them.
**The Campbell-Hagerman College for Girls opened in 1903 at the former Thomas January House on West Second St. in Lexington, KY. The college closed in 1912 and after several incarnations it was subdivided into apartments in 1960. My grandmother was born in 1885 so it's likely that she was in one of the first classes.