Galaxies

Galaxies are massive spacial bodies comprised of solar systems, asteroids, comets, stars, nebulae, dust, metals and rocks, and a black hole typically at the center of each and every one. Without galaxies, solar systems would have no rhyme or reason to their structure, and would likely fall to pieces due to the lack of gravitational push and pull that holds all galactical bodies together. In essence, we need galaxies to survive.

Some people get the order of these heavenly bodies confused. Here is the correct order from largest body to smallest:

Universe -> Galaxies -> Solar System -> Sun(s) and Planet(s)

There are also 4 major types of Galaxy. These can give your articles on these bodies more detail:

Spiral (Subgroups - Barred or Ordinary) - Irregular - Elliptical - Lenticular

