de Vaucouleurs classification

The de Vaucouleurs classification is a detailed system for categorizing galaxies, building upon the earlier Hubble scheme. While Hubble's system broadly divides galaxies into ellipticals, spirals, and irregulars based on their visual appearance, de Vaucouleurs's system offers a much more granular approach. It includes numerous codes to describe various morphological features, such as the presence and type of spiral arms, bars, and rings.1

This scheme categorizes galaxies into classes like ellipticals (E), lenticulars (S0), spirals (SA, SB, SAB), and irregulars (IA, IB, IAB). Each class is further subdivided into families, varieties, and stages, allowing for precise descriptions of a galaxy's structure. For example, spiral galaxies are detailed by the presence of a bar (SB) or lack thereof (SA), the tightness of their arms, and the size of their nucleus. The de Vaucouleurs system is more of a descriptive code than a commonly used classification scheme due to its extensive detail.1