Let’s Talk About Time

Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future. Time is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as a fourth dimension, along with three spatial dimensions.

Units of Time Through History

The Egyptian civilization is often credited as being the first civilization that divided the day into smaller parts, due to documented evidence of their use of sundials. The earliest sundials divided the period between sunrise and sunset into 12 parts. Since sundials could not be used after sunset, measuring the passage of night was more difficult. Egyptian astronomers noticed patterns in a set of stars however, and used 12 of those stars to create 12 divisions of night. Having these two 12 part divisions of day and night is one theory behind where the concept of a 24-hour day originated. The divisions created by the Egyptians however, varied based on the time of the year, with summer hours being much longer than those of winter. It was not until later, around 147 to 127 BC that a Greek astronomer Hipparchus proposed dividing the day into 12 hours of daylight and 12 hours of darkness based on the days of the equinox. This constituted the 24 hours that would later be known as equinoctial hours and would result in days with hours of equal length. Despite this, fixed length hours only became commonplace during the 14th century along with the advent of mechanical clocks.

While many different calendar systems were developed by various civilizations over long periods of time, the calendar most commonly used worldwide is the Gregorian calendar. It was introduced by Pope Gregory XIII in 1582 and is largely based on the Julian calendar, a Roman solar calendar proposed by Julius Caesar in 45 BC. The Julian calendar was inaccurate and allowed the astronomical equinoxes and solstices to advance against it by approximately 11 minutes per year. The Gregorian calendar significantly improved upon this discrepancy.