The feature used to classify galaxies is their **shape**. Galaxies can be classified based on their overall shapes, and the three main categories for classifying galaxies by shape are elliptical, spiral, and irregular. Here's a brief explanation of each shape:
1. **Elliptical galaxies**: These galaxies are shaped like ellipsoids or ovals. They are often reddish in color and have older stars. Elliptical galaxies do not have well-defined spiral arms.
2. **Spiral galaxies**: These galaxies have a distinctive spiral arm structure. They are often bluer in color due to the presence of younger stars actively forming in the spiral arms. The Milky Way is an example of a spiral galaxy.
3. **Irregular galaxies**: These galaxies do not have a distinct regular shape like elliptical or spiral galaxies. They can have chaotic and irregular shapes. Irregular galaxies often contain a lot of gas and dust, which can lead to active star formation.
By observing the shape of a galaxy, astronomers can gather information about its age, composition, and evolutionary history. Therefore, classifying galaxies based on their shape is an essential aspect of studying the universe and understanding the diversity of galaxies within it.
