How many letters does the top answer for “the theory and practice of navigation through air or space” have?

The most common answer is aeronautics (11 letters).

Crossword clue: the theory and practice of navigation through air or space

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

aeronautics 11 letters wn-def

the theory and practice of navigation through air or space

astronautics 12 letters wn-def

the theory and practice of navigation through air or space