ABSTRACT
Irregular galaxies are grouped into two types. The first one, denoted by Irr I, includes those with highly resolved O and B type stars and H II regions, while the second, Irr II, includes those whose images are completely smooth in texture. De Vaucouleurs developed a revised system of galaxy classification in 1956 when he published a list of southern galaxies which he observed at Mt. Stromlo Observatory in Australia. In 1960, when he was at the David Dunlap Observatory, van den Bergh showed that a correlation exists between the appearance of the spiral arms and the absolute luminosity of galaxies. Whichever scheme is used, the classes of galaxies have been determined mainly by visual inspection of the photographic image, based on morphological features such as the general shape, the appearance of spiral arms and bars, the relative proportion of the spheroidal component in size and luminosity, and so on.
