Preposition ”on” or ”in” ?

The correct one is: [On a starry night].

According to the preposition of time, [at] is used for the time of the day, [on] is used for a day or a night, and [in] is used for the month or the year.

Examples:

at 3pm
at 6 o'clock
at noon

on Saturday
on a Saturday
on July 4th
on a wonderful day
on a cold night
on a starry night


in September
in a very hot month
in a war- torn year

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