Explain the differences in appearance among normal spiral, barred spiral, elliptical, and irregular galaxies

Spiral galaxies are generally classified as galaxies that are circular in nature, with a bright nucleus that is enclosed by a thin outer disc. Normal spiral galaxies and barred spiral galaxies differ in appearance because normal spirals have 'arms' that emanate from the nucleus (which looks like a sphere that has curved arms coming out of the nucleus center), while barred spirals have bars (bright line features) that go straight through the nucleus, with arms that unwind from the ends of the bar. Elliptical galaxies look like very bright stars - they are shaped like elongated spheres, emanate a lot of light (but the brightness is concentrated in the center and dissipates the further out from the center you go), and vary in size. Irregular galaxies are classified as such because they don't fit into either the spiral or elliptical galaxy groups. They have a wide variety of shapes and sizes, and have no inherent regular or symmetrical structure.