The word "astronomised" is spelled with the IPA phoneme /ɒn/ rather than /ən/ because it follows the pattern of verbs with the prefix "astro-" such as "astrology" and "astronomy." The second syllable is spelled with the phoneme /aʊ/ because it is pronounced with a diphthong sound. The final syllable is spelled with the phoneme /aɪz/ to indicate that it is in the past tense and has been made into an action. Therefore, "astronomised" is the correct spelling for the past tense of the verb "to astronomize."