• The difference between a galaxy and the universe only begins and ends with size.

• Our solar system is part of a galaxy that contains millions of stars like our sun.

• There are billions of such galaxies in the universe.

• It is impossible to make conjectures about the size of the universe with current knowledge and tools.

• It is better to think of our galaxy, the Milky Way, as a speck of light in the Universe.

So our earth is part of the solar system. Our solar system is part of our galaxy, the Milky Way. The Milky Way has billions of stars. When billions of galaxies like the Milky Way come together, it's called the universe.