This is the 12314th most frequent Russian word.
июльскому
The word "июльскому" is the dative singular form of the adjective "июльский," which means "July's" or "related to July" in English.
In this context, 'July' is used as an adjective modifying 'celebration', indicating that the celebration pertains to the month of July.
Мы все готовимся к июльскому празднику.
We are all preparing for the July celebration.
Here, 'July' describes the train, specifying that it operates during the month of July.
Я купила билет на июльский поезд в Москву.
I bought a ticket for the July train to Moscow.
In this case, 'July' modifies 'sunlight', placing emphasis on the light associated with the month of July.