The Inception of Leap Seconds

As seen in USNO Time Service Announcements

The United States Naval Observatory has had several series of publications about their determination of time and their radio broadcasts of time signals. Among those are several different series of Time Service Announcements. Time Service Announcements generally gave detailed explanations of changes in the theory and practice of time scales and their uses.

Gernot Winkler was Time Service Director of the USNO. Winkler was one of the people who suggested that the leap second was the solution to the problem of radio broadcasts of time signals. During discussions before the inception of leap seconds Winkler co-intervened saying that automated navigation systems cannot tolerate leap seconds. Winkler was the vice president of IAU Commission 31 (the International Commision of Time) at the inception of leap seconds. Winkler presided over the chaos during the IAU Commision 31 meeting which followed the CCIR decision to create leap seconds.

After the CCIR decision had been made Winkler wrote several USNO Time Service Announcements to explain the changes that were about to happen to radio broadcast time signals.

Time Service Announcement series 14 number 7 (1970-10-23)

Winkler wrote that "time of day" was mean solar time which was fundamental for astronomical and navigational purposes, and also for the civil and legal use. Astronomers had repeatedly been saying this same thing since 1948 when Ephemeris Time was first proposed.

Winkler wrote that experience had already shown that many users did not willingly make time steps nor changes in frequency.

Winkler also wrote that the radio broadcasts of the automated navigation systems LORAN-C, OMEGA, and TRANSIT (NAVSAT) would not have steps of time.

Time Service Announcement series 14 number 8 (1971-10-08)

Winkler reiterated the impending change of broadcast time signals with copious references, and he gave detailed instructions for converting between the old broadcast time scale and the new broadcast time scale.

Time Service Announcement series 3 number 27 (1971-11-30)

Winkler reiterated that OMEGA would not implement steps of 1 second. Instead OMEGA would remain close to International Atomic Time.

Leap Seconds are not for Navigation

These Announcements make it clear that systems requiring precise time and frequency, in particular those systems which were specifically designed for automated navigation, intentionally ignored the CCIR recommendation that broadcasts should have leap seconds.

Leap seconds were for humans, not for machines. Leap seconds preserved the connection between time and date so that one calendar day remains defined by one rotation of earth. Leap seconds allowed the "frequency is paramount" voices at the CCIR to get what they wanted without having to explain a change in the legal definition of the calendar day for every member nation of the CCIR.

Rather than implement leap seconds, the radio broadcasts time signals for navigation implemented a different time scale. Astronomers had been explaining since 1948 that it would be necessary to employ a strategy of two separate time scales, one for humans and their calendars, and one for applications that required precision.

Discussions among delegates to the CCIR inexplicably rejected the notion of two time scales. The world could have had two internationally-approved time scales, each of which had clear purpose and applications, but the world has only one internationally-approved time scale. Above it is clear that various different systems rejected the idea of a leap second since before the first one was inserted. Different systems have adopted different workarounds, and that means that they do not agree about the answer to the question:
"What time is it?"

Steve Allen <>
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