By Dr. Saira Latif, Added: 2026-05-12
We all know about time , and with high flare of confidence, we perceive it quickly. Despite we realise its important in our lives no matter how often we forget about it completely in spur of moment!:))
Just a few days ago, a leap day has passed. And that brought me back to think about time again for a while.
Invention or construct of time and its measurement is one of the an incredible discovery of human collective intellect and this is long but interesting story. However , it is fascinating to give it a thought that how it matters in our life and how it is measured.
Precise time measurements are important to estimate/guess when an event took place in past(tracing) or would take place in future(tracking). Through time we make sense of world around us. Its significance span over in age estimation of living organism and stars , prediction of astronomical events, agriculture, navigation and positioning etc are just few to mention.
Article content Photo Credit: NASA: Satellites Navigation Such estimates would not be possible if we were not be able to numerate or develop timescales in relation to relatively stable recurring natural phenomena such as rotation of earth, moon phases, change of seasons, atomic energy transitions etc. Precision of our estimates then depends on how stable are these naturally reoccurring phenomena are.
The two of most precise timescales are derived in relation to rotation speed of Earth relative to Sun and radiations produced by cerium 133 atom.
Astronomical time is the time synchronise with the rotation of earth that means our clock are sync with rotation speed of earth around Sun. Every tick or second is sync with the duration earth take to reach one part to another part of 86,400 parts that collectively make up 24 hours duration as developed by ancient greek and Persian scholars. Due to various factors such as tidal friction and other geophysical processes, Earth’s rotational speed is not constant. Therefore the length of a day as measured by the rotation of the Earth is also not constant.It is observed that on average the Earth’s rotation experiences a gradual slowdown.
Article content Image Capture using Celestia open source Simulation Software The variations in earth rotation speed leads to variations in the length of an astronomical second over time. To account for these variations and maintain consistency , periodic adjustments such as adding leap seconds are made to Coordinated Universal Time (UTC) to keep it in sync with International Atomic Time (TAI).
International Atomic Time (TAI) on other hand is based on atomic second.The atomic second is a fixed unit of time based on the measure of vibrations of atoms to determine time. The current definition of the atomic second is based on the cesium atomic clock, where one atomic second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. The transition between the hyperfine levels of the ground state of cesium-133 is a key component in the operation of atomic clocks, which rely on the stability and precision of this transition for timekeeping. This specific transition involves the absorption or emission of microwave radiation at a frequency of approximately 9,192,631,770 Hz. This frequency is equivalent to a wavelength of about 3.26 centimeters.
The length of an atomic second differs from that of an (astronomical) second, leading to discrepancies between the atomic second and the (astronomical) second. These variations result in a slight divergence between the duration of a day as measured by the astronomical timescale and the atomic timescale.
Small irregularities in the Earth’s rotation speed may not noticeably disrupt daily tasks, but when these deviations accumulate over time, they can influence how we perceive time, adhere to schedules, and maintain routines. Timekeeping systems, including the occasional addition of leap seconds, are implemented to align human activities with precise astronomical time standards and mitigate these effects.
Source of factual Information:
Miscellaneous from internet, National geographic, NASA, Celestia