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  • The Reason Leap Second Is Abolished

    The Reason Leap Second Is Abolished

    UTC has kept pace with the Earth’s rotation through the use of leap seconds. However, this will no longer be the case, as the General Conference on Weights and Measures (CGPM) has decided that no leap seconds will be added after 2035. While this decision was taken to avoid disruptions and anomalies during the transition to digital systems, it could lead to a discrepancy of about one minute between global time and the Earth’s rotation by then.

    In Use Since 1972

    A day (in theory) consists of 86,400 seconds because the Earth’s rotation determines the speed of our time. However, the actual speed of the Earth’s rotation varies.


    The Moon in particular has a long-term retarding effect, in addition to seasonal, seismic, and climatic factors. The moon’s gravity causes an increase in day length of about 1.78 milliseconds per century. In contrast to this model, by 2020, the Earth’s rotation had accelerated significantly.

    UTC has added a total of 27 leap seconds since its inception in 1972.

    Since 1972, leap seconds have been used to keep the official Universal Time (UTC) synchronized with the Earth’s rotation: if the deviation is 0.


    9 seconds or more, an additional second is added before midnight on New Year’s Eve or mid-year. Thus, the last minute of last year has 61 seconds. The last time something like this happened was on New Year’s Eve 2016.

    Inconsistent and Perhaps Risky

    The issue, however, is that introducing a leap second is not trivial for many digital systems that rely on atomic clocks. Just before the changeover, the clocks can be adjusted to halt the seconds for a second, add an extra second (for a total of 61 seconds), or slow down the fundamental clock pace. This has been dealt with in many ways up until now, depending on the nation, the firm, or the organization. For instance, Google progressively reduce the additional second in the 24 hours before the changeover.

    Therefore, the leap second might cause temporary discrepancies among the different time standards. Such little delays, even if measured in microseconds, may have major repercussions in the digital and financial sectors. The Global Positioning System (GPS) system does not account for leap seconds, although the Russian GLONASS system does.

    Prior to this point, leap seconds were used to synchronize global clocks with Earth’s rotation.

    Also, in 2020, the Earth briefly sped up its spin, which might theoretically lead to a negative leap second. This is the first time in history that global time has been shortened by a single second. Therefore, it is not apparent whether this is even theoretically possible.

    100 Years Pause for Leap Seconds

    These considerations led to the CGPM’s recent decision to alter the leap second system. It has been debated for a long time how much time should be added or subtracted from universal time to account for Earth’s rotation. This is due to the fact that essential digital infrastructure is always susceptible to major breakdowns. That’s why the organization went ahead and increased the allowable variance.


    For example, after 2035, no further leap seconds will be added for at least the next 100 years. World time and the Earth’s rotation may diverge by up to one minute during this period. However, in normal life and for most time-sensitive applications, this wouldn’t make a difference since the time zones and the system of summer and winter time entail significantly bigger variations anyway.

    The rotation of the Earth is the standard by which we measure global time.

    It’s Unclear How This Will Be Implemented at This Time

    Global organizations are also tasked with settling on a threshold for tolerable variation by 2035. This largely includes the International Telecommunication Union (ITU), a United Nations institution responsible for regulating the technical elements of telecommunications, in addition to the General Conference on Weights and Measures (GCWM). As such, this group would be tasked with making the halt for the leap second and any potential new rule a reality.

    It was still not a unanimous decision at CGPM. As a result of the necessity for more time to implement the technological changes, Russia chose to postpone the leap second until 2040. But the decision made during the General Conference is still in effect for the time being. It remains to be seen whether and when it will be put into operation and if other nations will thereafter follow suit.

  • What Is Time? And How Can It Be best Defined?

    What Is Time? And How Can It Be best Defined?

  • Invention of the Clock and the History of Time

    Invention of the Clock and the History of Time

    The modern perception of standardized time is shared across the most distant lands. It combines knowledge of the astronomical calendar with state-of-the-art clockwork based on the movements of the stars and planets and is equipped with the latest technology to record and measure relatively short intervals of time.

    Humankind was probably aware of the passage of time at the dawn of reason, but it was only with the beginning of settled agriculture around 8000 BC that a proper understanding of the seasons and daily changes over the course of a year became important. Prehistoric monuments around the world, including Stonehenge in England, clearly show that the seasons could be tracked by the setting and rising of the sun.

    The Invention of Time and the Clock

    The need to measure small intervals of time only emerged in the advanced civilization of ancient Mesopotamia around 2000 BC, probably due to religious, ritual and administrative requirements. Sundials were used to keep track of roughly day time, while shorter time intervals were measured by following the drip of water or the flow of sand through a fine gap.

    The earliest weight-driven mechanical clocks probably appeared in Europe in the 2nd millennium AD. A single clock mounted in a public structure, such as a church, is sufficient for an entire community. Mechanical clocks became portable after the discovery of spring powering around 1500, and their precision was greatly improved in the late 17th century. The Industrial Revolution, which led to faster travel and telegraphic communication, eventually made it imperative to keep a record of time across large areas.

    2000 BC: First Calendars

    The ancient Babylonian civilization developed the earliest known form of calendar. The year was divided into 12 months based on the lunar cycle, with an extra month added to align the lunar and solar cycles. Other civilizations developed similar calendars

    1600 BC: Water Clock

    Although probably developed in Mesopotamia, water clocks (clepsydra) were popular in Greece and Rome. Graduated marks kept track of the level of water in a vessel with a small hole in the bottom.

    1600 BC: Water Clock

    1500 BC: First Solar Calendars

    The first solar calendars, developed in Babylon and Egypt, tracked time by the shadow cast by an upright stick called a gnomon.

    520 BC: Candle Time

    As mentioned in a Chinese poem, the first candles, which roughly revealed the time even at night, were useful thanks to the slow burning of a candle or incense stick.

    800 BC: Hourglass

    The first mention of these sand-based clocks dates back to the 14th century, just like water clocks, but sand clocks were probably discovered in Europe as early as the 9th century, or at least introduced there.

    1088: Clock Tower of Su Song

    The Chinese scholar Su Song built a clock tower that is believed to have advanced clockmaking in Europe, using a series of complex gears that track astronomical cycles.

    su song saat kulesi 1

    13th Century: Weight-Driven Mechanical Clocks

    The earliest known mechanical clocks, found in English cathedrals such as those in Salisbury and Norwich, used a falling weight on a chain to drive the rotation of gears set by an escapement and oscillating mechanism.

    1430: Spring-Driven Clocks

    Watches were powered by a discharged spring, which helped to reduce the size of the watches. Watchmaker Peter Henlein used this technique in his first pocket watch.

    1656: Huygens’ Pendulum Clock

    Dutch inventor Christiaan Huygens used the regular oscillations of a weighted pendulum to make a clock that kept time every day with an error of a few seconds.

    1759: Marine Chronometer

    British watchmaker John Harrison perfects a spring-operated chronometer capable of keeping precise time for long periods at sea, allowing for the first time precise longitude calculations while on board a ship.

    1759: Marine Chronometer

    1927: Quartz Watch

    The first electronic clock was made using natural electricity generated by the rapid oscillation of a quartz crystal. This clock could measure time to the precision of a fraction of a second per day.

    1947: Atomic Clock

    This device uses fast transitions in the internal structure of elements such as cesium to measure time with great precision.

    1967: Defining the Second

    One second was redefined as the time it takes a cesium atom to travel between two energy levels 9,192,631,770 times.

    The 1970s: Numerical Timekeeping

    The use of liquid crystals to show the change of digits in digital devices represented a revolution in time measurement.

    Sources:

    • Landes, David S. Revolution in Time: Clocks and the Making of the Modern World. Cambridge: Harvard University Press (1983).
    • Landes, David S. Clocks & the Wealth of Nations, Daedalus Journal, Spring 2003.
    • Lloyd, Alan H. “Mechanical Timekeepers”, A History of Technology, Vol. III. Edited by Charles Joseph Singer et al. Oxford: Clarendon Press (1957), pp. 648–675.