In these galaxies the spiral arms are often resolved into luminous stars, clusters of stars, and bright emission nebulae. In between these two extremes are the Sb and SBb galaxies, which display intermediate characteristics. Our Galaxy, and our neighbor M31 are both Sb galaxies. Now lets discuss the last class of galaxies, the irregulars. Irregulars Irregular galaxies show no trace of circular or rotational symmetry but have an irregular or chaotic appearance.
Many irregulars show evidence of hot, young stars and gaseous nebulae.
Some also have conspicuous dark lanes of absorbing interstellar dust. Irregular galaxies are relatively rare, as only a few percent of the brightest galaxies in the sky are irregulars. Irr - NGC3034 Review Questions Let's review the basics of galaxy types with a few questions. A photograph of an elliptical galaxy is measured with a ruler, and you find that the longest axis of the elliptical is 4 inches in length, while the shortest axis is 2 inches.