In meteorology for the Northern hemisphere, autumn or fall begins on September 01, 2015. It is also called the beginning of meteorological fall. Autumn marks the transition from summer into winter when the arrival of night becomes noticeably earlier. The meteorological seasons are divided according to the calendar months. In the period before computers it simplified statistics. Therefore, meteorologists consider autumn to be the months of September, October and November.
Autumn in poetry has often been associated with melancholy. The possibilities of summer are gone on early fall, and the chill of winter is on the horizon. Skies turn grey, and many people turn inward, both physically and mentally.
Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, one or many colors that range from red to yellow. The phenomenon is commonly called fall colors and autumn colors. In some areas of Canada and the United States, "leaf peeping" tourism is a major contribution to economic activity. This tourist activity occurs between the beginning of color changes and the onset of leaf fall.
In the Northern Hemisphere, autumn is also associated with the Halloween season, and with it a widespread marketing campaign that promotes it, in the U.S.A. The television, film, book, costume, home decoration, and confectionery industries use this time of year to promote products closely associated with such a holiday. (With material from: Wikipedia)