These multitudes of galaxies come in a variety different shapes and sizes. In this exercise, we'll take the first steps in learning about these many different types of galaxies. To help us understand the complexity of galaxies, astronomers have developed several schemes to classify them into broad groups based on their morphological structure. Hubble seperated galaxies into three broad groups, based upon their morphology . He classified galaxies as elliptical, spiral and irregular.
Elliptical galaxies are spheroidal in shape, and range from perfectly round to quite flattened.
They are designated by the letter E , followed by a number which describes the degree of flattening. Spirals, on the other hand, are thin disks with a central bulge and arms that wind out from the center. Spirals are designated by the letter S , followed by other letters that describe the size and strength of the spiral arms, as well as the relative size of the nucleus. Irregulars have no trace of circular or rotational symmetry but have an irregular or chaotic appearance. Irregulars are denoted by the letters Irr .