* Galaxies are vast collections of billions of stars, gas, dust, and dark matter held together by gravity. Our own galaxy is called the Milky Way.

Let's look at why the other options are incorrect:

* Solar systems are made up of a star and the planets, moons, asteroids, and other objects that orbit it.

* Constellations are patterns of stars that appear close together in the sky from our perspective on Earth. They are not physical groupings.

* Planets are large celestial bodies that orbit a star.

Let me know if you have any other questions!