Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
Observatory is regular. It follows the -ies Conversion rule.
Use plural verbs: "The observatories are ready" (not "is ready").
Yes. The plural observatories is standard across all English variants.
The word observatory follows the standard English pluralization rule. When forming the plural, observatory becomes observatories. This follows the -ies Conversion pattern, which is one of the most common plural rules in English.
Understanding why observatory becomes observatories helps with spelling and pronunciation. Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
When using observatories in writing, remember that it functions as a plural noun in sentences. It pairs with plural verbs and pronouns. For example: "The observatories are ready" (not "is ready"). This subject-verb agreement is essential for grammatical correctness.