Ralph Waldo Emerson (1803-1882), perhaps best known for his essay Self-Reliance (1841), was one of America's most influential thinkers and writers. After graduating from Harvard Divinity School, he followed nine generations of his family into the ministry but practiced for only a few years.
The first menstrual period is called  menarche .. The menstrual cycle is about four weeks long, starting on the first day of bleeding and ending when the next period begins. However, it can vary greatly when a girl first starts her period. It may skip months or come several times per month in the beginning.
The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days). Bleeding usually lasts around 2 to 7 days. Menstruation stops occurring after menopause, which usually occurs between 45 and 55 years of age.