Which characteristic is used to classify galaxies? 1. the size of the galaxy

2. the shape of the galaxy

3. the presence of dust and gas between stars

4. the presence of active star formation sites

2. the shape of the galaxy

Explanation:

There are four classifications of galaxies and these are: spirals, barred spirals, ellipticals and irregulars. It was Edwin Hubble, an American Astronomer who identified them. They were given such names owing to their shapes. For example, the spiral galaxy looks like it is rotating while the barred spiral galaxy also looks rotating yet it has a bar at the center. Elliptical galaxies have an elliptical shape, similar to that of an elongated circle or an egg. Irregular galaxies don't stick to a particular shape.

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