What are Galaxies classified by?

There are four main categories of galaxies: irregular, elliptical, barred spiral, and spiral.

The shapes of spiral galaxies vary, and they are categorized based on the dimensions of their bulge, as well as the tightness and appearance of their spiral arms.

The bulge's stars are older and redder than those in the spiral arms, which wrap around the galaxy. Yellow stars similar to our Sun can be found all over the disk of a spiral galaxy.

Spirals galaxies with a bar-shaped cluster of stars spanning the galaxy's center are known as barred spiral galaxies.

Elliptical galaxies are smooth, oval-shaped, and devoid of arms and a disk. They are primarily composed of old stars and have low gas and dust contents.

Having neither an elliptical nor a spiral shape, irregular galaxies are typically smaller objects with a high concentration of gas and dust and hotter, younger stars.

The majority of the bright, nearby galaxies are either elliptical, barred, or spiral galaxies.

Galaxies are classified primarily by their shapes, which include spiral, elliptical, and irregular. These classifications are based on the appearance of the galaxy's structure and are determined by characteristics such as the presence of spiral arms, the degree of ellipticity, and overall symmetry. Additionally, galaxies can be further categorized based on their size, luminosity, and other properties.