Extra-galactic nebulae

"Extra-galactic Nebulae" by Edwin Hubble is a scientific study from the early 1900s that investigates celestial objects outside our galaxy. The study kicks off with a summary and introduction, setting the stage for a breakdown of 400 faraway nebulae, noted for their brightness and shape. Hubble’s classification reveals that nearly all of these nebulae have orderly structures, often spinning around a center point, while only a few appear oddly shaped. By exploring the connections between brightness, size, and how far away these nebulae are, Hubble lays the groundwork for categorizing them into elliptical, spiral, and irregular types, hinting that these categories might represent stages in how these celestial objects develop over time.