It helps if you think about how you ask the time: "Che ore sono?" In English, it means what time is it, but italians say "how many hours are there?" So if it's 9, they say "sono le nove", meaning "there are nine". Sounds weird in english, but that's language learning for you :)
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In Italian time is expressed with plurals (sono le nove, sono le otto, sono le undici), just look at the number, it is always in plural, and is always feminine.
•sono le otto - it's eight o'clock.
•sono le dieci - it's ten o'clock.
the only exception is one, which is expressed in singular:
•è l'una. - it's one o'clock
questions to use are as follows:
•che ora è?
•che ore sono?
you see, that singular "ora" gets singular "è" while plural "ore" gets plural "sono". very logical if you ask me.
to express midnight/noon we use singular as well:
•è mezzogiorno - it's noon
•è mezzanotte - it's midnight