Probably the most essential to the core of the Indian culture itself; Ragas are to the Indian culture like what the blues are to the African-Americans, and what rhythm is to the Brazilians.
Indian classical music is interwoven into each and every one of us whether we care to accept it or not.
One of the most unique aspects of the Ragas is the 'Samay', which dictates which raga is most effective at a particular time of the day, as well as even attributed to the seasons.
In fact, it is said that a raga can even evoke the feeling of the season it reflects in another season, for e.g. if you simply wished to evoke the mood of a monsoon day, you could perform Megh Malhar; even in the middle of summer.