A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2022 Nov 23, 09:02 -0800
We don't keep time by the Sun on our ordinary clocks, and we haven't for a long time. Average offsets during the course of a year:
- 8 minutes offset from Sun, beginning 250-300 years ago when mechanical clocks and watches superseded sundials,
- 15 minutes more, beginning almost 140 years ago from time zones,
- 15 minutes from time zone creep during the past century (averaging, actual adjustments can be much more),
- 40 minutes annual average from "daylight time", beginning about 100 years ago,
- a fraction of one second under current UTC rules, beginning 50 years ago,
- if leap seconds are dropped, less than about one minute before the year 2100.
All of these steps have long since separated us from the Sun. It is not "local noon" when the clock says 12:00. We do not keep time by the Sun except in a long-term average sense. It is not at at all unusual for clocks reading "normal time" to differ today by 90 minutes from local apparent time. Dropping leap seconds would change this only by about two seconds per year in later decades in this century. Surely we recognize that this is nothing compared to 90 minutes, right??
The negative navigational consequences of dropping leap seconds are trivial. Dropping leap seconds would add one small task to a celestial navigator's work: adding the adjustment (UTC-UT1) to the time before entering a nautical almanac (technically we should do this even now but very few celestial navigators have any requirement for that additional accuracy). This is nothing more than a simple "watch error" adjustment.
And let's remember that celestial navigators are a rare breed! Meanwhile, innumerable systems in many fields of human endeavor with software governing synchronization must be designed with uncertain rules for future time. There is no way today to predict how many seconds will elapse between 17:00:00 UTC on November 23, 2022 and 17:00:00 UTC on November 23, 2032. This is an arbitrary and uncertain component of our calendar, and it is a potential source of bugs and errors that will come back to bite us if we do not fix it in advance. Dropping leap seconds is a simple and efficient solution to this problem. It does entail some expense, and there are risks in any implementation, but those risks are finite and contained. We should not exaggerate the supposed merits of a fanciful and entirely historical connection between normal time-keeping and apparent solar time.