Which astronomical unit includes our Solar System, Earth, and the Milky Way galaxy?

The correct answer is the Universe. The Universe encompasses everything that exists, which includes all galaxies, solar systems, planets (such as Earth), and various celestial phenomena. It is the broadest term that reflects the totality of space and time, along with all matter and energy within it.

In contrast, a galaxy refers specifically to a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The Milky Way is a specific galaxy that contains our Solar System but does not include other galaxies or the entirety of the cosmos.

A galactic cluster is a collection of galaxies that are gravitationally bound to each other. This term describes a smaller scale compared to the Universe, which also includes many galactic clusters.

A planetary system typically refers to a star and the celestial bodies that are in orbit around it, such as planets and moons. Our Solar System is an example of a planetary system, but it is only one of countless such systems within the Universe.

Thus, the Universe is the encompassing term that includes all that is mentioned in the question.