Year (yr)
The year, symbol yr, is the time Earth needs to go around the sun—about 365.242 days. People have tracked years for farming and religion for a long time, creating calendars. The Julian and then the Gregorian calendars made the year’s length more exact by adding leap years. Today, the year is used everywhere for history, science, work, and culture. Years are closely linked to how people see seasons and life’s cycles.
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.