Observatory adjectives are listed in this post. Each word below can often be found in front of the noun observatory in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing OBSERVATORY.
astronomical, great
meteorological, national
new, private
small
Hope this word list had the adjective used with observatory you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.
Please add more adjectives to make this list more complete: