EVERYDAY SCIENCE

Detailed explanation-1: -Astronomers classify galaxies into three major categories: elliptical, spiral and irregular.

Detailed explanation-2: -While not classified in the Hubble Classification System, irregular galaxies are classified into three categories: Irr-I (Irregular one), Irr-II (Irregular two) and dIrr (dwarf irregular).

Detailed explanation-3: -An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.

Detailed explanation-4: -Hubble recognized these two types of irregular galaxies, Irr I and Irr II. The Irr I type is the most common of the irregular systems, and it seems to fall naturally on an extension of the spiral classes, beyond Sc, into galaxies with no discernible spiral structure.

Detailed explanation-5: -Irregular galaxies are the most unusual of galaxies. They don’t seem to fit into either the spiral or elliptical galaxy categories. They don’t have nice spiral arms, but they do have dark patches of gas and dust. Some irregular galaxies clearly look like two galaxies ran into each other!