Many people fail to realize that astronomical objects such as the Earth or Sun should have their first letter capitalized. The most plain and obvious reason is that both of those words are proper nouns, and proper nouns should be capitalized because they can be seen as either a place or a thing.
It’s fairly simple to write something like, “The sun is at the center of the solar system.” But those are errors when writing. Again, both the Sun and Solar System are proper nouns so they should automatically be capitalized.
The International Astronomical Union (IAU), which is the official authority on naming celestial things, the structure of astronomical papers, and astronomical grammar, does not have the authority to fully demand capitalization all the time. Different countries have different rules in remarks to their grammar. The IAU Style Manual states, “The use of capitals for the initial letters of words is much more common in English (and German) than in French,” but they do recommend that astronomical objects should be capitalized in both languages.
This is what the IAU recommends in reference to astronomy capitalization, “The initial letter of a word should be typed or printed as a capital in the following cases…individual astronomical objects (such as Earth, the Solar System, Orion, the Crab Nebula, Galactic Centre)…[and] names of individual objects or instruments (Voyager 2).”
It is important to capitalize the Andromeda Galaxy just as its important to capitalize the White House. All things in astronomy are wonders, are proper, and are worth the extra effort to be capitalized.