Day (d)
The day, symbol d, is the time it takes Earth to rotate once. A day is 24 hours or 86,400 seconds. Because Earth’s spin changes a little, days can vary, so leap seconds are sometimes added to atomic clocks. The day is a key part of human life, shaping calendars, routines, and events in all cultures. It is one of the most fundamental and widely recognized time units.
Week (wk)
The week, symbolized by wk, is 7 days long. Its history is rooted in ancient traditions, including Babylonian, Jewish, and Roman customs. The seven-day week originated because of religion and culture, and later became established through Christianity and Islam. Although the week is not based on astronomy, it is now widely used in calendars and daily life. Its long use shows how strong traditions are in setting time.