Radio Station WWV - Morse Code UT2 Correction 'SU019' (1969) by shortwavemusic published on 2012/09/20 02:43:45 +0000 A few detailed words about the UT family of time codes: Universal Time (UT) is derived from measurements of the Earth’s rotation on its axis relative to the sun. However, since the Earth’s position, angle, and rotational speed are not constant, the International Astronomical Union created several categories of Universal Time which compensate for these variables. The three categories are UT0, UT1, and UT2. UT0 represents the values of UT as obtained by visual observation of star transits at various observatories. These raw values differ slightly from each other due to the effects of polar motion - a discrepancy corrected by UT1, which gives the precise angular coordinate of the Earth about its spin axis. A third correction, UT2, accounts for annual changes in the Earth's rotational speed. Coordinated Universal Time (UTC) is obtained from an atomic time scale that has been adjusted to remain close to UT1 (earth rotation time), thus keeping solar time in close coordination with atomic time. “Pure” atomic time is kept in a standard known as TAI (International Atomic Time), which is not adjusted for Earth factors. Although WWV now makes real-time adjustments for UT1 and UT2, these discrepancies were originally announced in Morse code for manual correction by users during the 19th minute from WWV and the 49th minute from WWVH. The two codes used were “AD” (Add) and “SU” (Subtract), followed by a three-digit number which represented the UT2 correction in milliseconds. In the recorded example, “SU 019” instructs observers to subtract 19 milliseconds over the course of 24 hours to properly calculate the present UT2 offset. The UT1 correction can still be heard in the modern broadcast format of WWV in the form of the ‘double tick’ heard during each minute. If Earth time is “fast” relative to UTC, the double-ticks will be placed immediately after the start of each minute. However, if Earth time lags behind UTC, the double-ticks begin after the 8th second. Each double-tick represents one-tenth of a second that UT1 is offset from UTC. For example, if the first, second, and third pulses of the minute are doubled, then UT1 is three-tenths of a second faster than UTC. If the ninth and tenth pulses are doubled, then UT1 is two-tenths behind UTC. Track 13 of 'AT THE TONE: A LITTLE HISTORY OF NIST RADIO STATIONS WWV & WWVH.' © 2009 Myke Dodge Weiskopf / Obscure-Disk. To order this compilation on CD, please write firstname.lastname@example.org.