Raga literally means "color" or "mood", as the ragas are said to "color the mind" according to the specific moods evoked in the music. Ragas are essentially melodic modes used in Indian classical music, upon which the musician composes and improvises.
It is said that there are thousands of ragas in existence but approximately 150 or so in use today. In the Indian musical tradition, each raga is associated with a particular time of day/night and some also with particular seasons. The instrumentalist or vocalist chooses the raga according to the time as well as the mood they wish to evoke. In addition to the scale, each raga has it's own unique features, such as particular ornamentation, intonation, important notes as well as forbidden notes or movements.
This wheel shows the ascending and descending scales of just one selection of ragas for each time of the day/night:
Click the play button to load the raga wheel