[LEAPSECS] first use of the terms UT0, UT1, and UT2

[Michael.Deckers]

    On 2017-10-14 22:57, Steve Allen wrote:
> Documents about the origin of the terms UT0, UT1 and UT2 have not been
> widely available.  In the issues of Bulletin Horaire from the BIH in
> 1955 I have found a detailed synopsis of the IAU GA which decided
> that the measurement of time should change in that fashion, and
> also what I believe is the first published use of those terms.
>
> http://www.ucolick.org/~sla/leapsecs/BH1955.html
>
> These show the tensions between astronomers, physicists, and radio
> engineers.  They provide insight into the level of understanding of
> various participants and the goals they were seeking.  They also hint
> at the incredulity of Nicolas Stoyko of the BIH as he got the answer
> to his question "You want it when?", because the IAU resolutions from
> 1955 required changes by every observatory, every radio broadcast of
> time signals, changes to all the computations at the BIH, and a whole
> new level of rapid coordination between the International Latitude
> Service and the BIH.

        Thank you for these interesting primary sources!

        They corroborate (or at least they are consistent with) the 
following
        secondary sources:

         ∙ Felicitas Arias and Barry Guinot who write:
               "The distinction UT0/UT1/UT2 was introduced in January 
1956. At the BIH,
                UT was an average of the UT0’s of the participating 
observatories."
            in "Coordinated Universal Time UTC: Historical Background 
And Perspectives".
            online at [syrte.obspm.fr/journees2004/PDF/Arias2.pdf]

         ∙ D H Sadler in "Mean Solar Time on the Meridian of Greenwich" in
           Quarterly Journal of the Royal Astronomical Society vol 19 p 
290..309. 1978,
           online at 
[http://articles.adsabs.harvard.edu/cgi-bin/article_queryform
                      ?bibcode=1978QJRAS..19..290S] who writes:
             "As a result of informal discussions between BIH and the former
              (H Spencer Jones) and current (Wm Markowitz) Presidents of 
[IAU]
              Commission 31 [on Time], the following terminology was 
adopted and
              used from 1956 January 1:
                  UT0 is Universal Time as formerly computed;
                  UT1 is UT0 corrected for observed polar motion;
                  UT2 is UT0 corrected for observed polar motion and for
                      extrapolated seasonal variation in the speed of 
rotation
                      of the Earth
              The adoption of this terminology was reported to 
Commission 31 at the
              1958 (Moscow) General Assembly [30: Trans IAU X, 489. 1960],
              but (although generally accepted) it appears never to have 
received
              formal approval by the IAU; it was not reported to 
Commission 4
              [Ephemerides], and was clearly intended for specialist use 
in the
              time services."

         ∙ the bio of William Markowitz in
           [http://ad.usno.navy.mil/wds/history/markowitz.html] who says
              "At the International Astronomical Union (IAU) meeting in 
Dublin in 1955 he
               proposed the system of UT0, UT1 and UT2 which went into 
effect within
               months and remains today."
            except that, nowadays, UT0 is useless because local sidereal 
time is
            a derived rather than an observed quantity, and UT2 is 
rarely used.

    Michael Deckers.