by Fred Steinhauser, OMICRON electronics GmbH, Austria
The General Conference on Weights and Measures (CGPM) which was held in November 2022, accepted the resolution “On the use and future development of UTC,” effectively ruling out the leap seconds for the foreseeable future.
Recently I rode in the co-driver’s seat in a modern rental car. Instead of classical meters and indicators in the direct view of Leap seconds have caused issues since they have existed. At the beginning this was only noticed by a few initiates who could not get through to their desire to abolish leap seconds. There have been initiatives to abandon them, such as the recommendation at the ITU-R Plenary in 2012, that was not adopted.
Some voices even denied any leap second related problems at that time. But since the big players in the computing business encountered problems during leap second insertions, the topic has gained momentum.
With the resolution from November 2022, the CGPM, in a smart way, does not propose to explicitly abandon the leap seconds as such, but to loosen the rule for applying leap seconds (a threshold for the predicted difference between UT1 and UTC). The matter was forwarded to ITU-R to implement a procedure until 2035, so that we will not encounter a leap second for at least a century.
Nevertheless, when searching for the pros and cons for abandoning the leap second, you could still find the argument it would make sundials obsolete. Let us look into this concern by estimating some ballpark figures.
If we assume the hand of the sundial to be a bar of 5mm thickness and being one meter away from the dial, the thickness of the hand corresponds to about 70 seconds.
But it will not even cast a sharp shadow of exactly this width. Due to the angular diameter of the sun being about 0.5°, the edges will be smeared over a blurred region corresponding to about 2 minutes. This gives a hint towards how limited the accuracy of a sundial is anyway.
But there is another, even more severe effect, coming from the facts that the earth’s orbit is not a circle but an ellipse and that the axis of the earth is tilted against the ecliptic. The keywords to search for are Analemma and Equation of Time. The time of the highest position of the sun, which indicates the local noon in apparent solar time, almost never coincides with noon as shown on our watches. In effect, it only matches on four days each year. On all other dates, the sundial is either leading or lagging, up to about 15 minutes! The extremes occur around middle of February and end of October. So, as sundials are regularly off by up to about 900 seconds, how would we notice a few more seconds accumulated by skipping leap seconds? There are more sophisticated versions of sundials that take the Equation of Time into account, but even those have uncertainties in the order of a minute.
And for example, the longitude difference between Madrid and Warsaw is almost 25°. Both cities lie in the CET zone, although the local apparent solar times differ by almost 100 minutes – with no relevant consequences. Now we know what we are talking about: sundials are already obsolete for a long time and will not pose an issue that should make us cling on the leap second.
In the meanwhile, earth has done us the favor to speed up its rotation a bit, so that no need for inserting a leap second came up since 2017. But if this acceleration goes on, we might even face the need for deducting a leap second. This will most likely have disastrous effects since the systems are not prepared for this and will behave even worse than during the insertion of a leap second.
Let us hope that ITU-R puts the measures in place before this happens.
Biography:
Fred Steinhauser studied Electrical Engineering at the Vienna University of Technology, where he obtained his diploma in 1986 and received a Dr. of Technical Sciences in 1991. He joined OMICRON and worked on several aspects of testing power system protection. Since 2000 he worked as a product manager with a focus on power utility communication. Since 2014 he is active within the Power Utility Communication business of OMICRON, focusing on Digital Substations and serving as an IEC 61850 expert. Fred is a member of WG10 in the TC57 of the IEC and contributes to IEC 61850. He is one of the main authors of the UCA Implementation Guideline for Sampled Values (9-2LE). Within TC95, he contributes to IEC 61850 related topics. As a member of CIGRÉ he is active within the scope of SC D2 and SC B5. He also contributed to the synchrophasor standard IEEE C37.118.
