Music is an art form whose medium is sound. Its common elements are pitch (which governs melody and harmony), rhythm (and its associated concepts tempo, meter, and articulation), dynamics, and the sonic qualities of timbre and texture. In its most general form the activities describing music as an art form include the production of works of music, the criticism of music, the study of the history of music, and the aesthetic dissemination of music.Shab-e Chella(-ye bozorg) ("night of (the great) forty", Persian: شب چلّه) or Shab-e Yaldā ("Yalda night" Persian: شب یلدا) is an Iranian festival celebrated on the "longest and darkest night of the year," that is, in the night of the Northern Hemisphere's winter solstice. Calendarically, this corresponds to the night of December 20/21 (±1) in the Gregorian calendar, and to the night between the last day of the ninth month (Azar) and the first day of the tenth month (Day) of the Iranian civil calendar.
The longest and darkest night of the year is a time when friends and family gather together to eat, drink and read poetry (especially Hafez) until well after midnight. Fruits and nuts are eaten and pomegranates and watermelons are particularly significant. The red colour in these fruits symbolises the crimson hues of dawn and glow of life. The poems of Divan-e-Hafez, which can be found in the bookcases of most Iranians families, are intermingled with peoples' life and are read or recited during various occasions like this festival and at Nowruz.