Time Service
The U.S. Naval Observatory operates two Master Clock facilities. The primary facility, in Washington, D.C. maintains 57 HP/Agilent/Symmetricom 5071A-001 high performance cesium atomic clocks and 24 hydrogen masers. The alternate master clock, at Schriever Air Force Base, maintains 12 cesium clocks and 3 masers. The observatory also operates two rubidium atomic fountain clocks, which have a stability reaching 7×10−16. The observatory intends to build several more of this type for use at its two facilities.
The U.S. Naval Observatory provides public time service via 26 NTP servers on the public Internet, and via telephone voice announcements:
- +1 202 762-1401 (Washington, D.C.)
- +1 202 762-1069
- +1 719 567-6742 (Colorado Springs)
The voice of actor Fred Covington (1928–1993) has been announcing the USNO time since 1978.
The voice announcements provide local and universal time every 15 seconds over a background of once-per-second ticks, with the ticks lengthened to prominent beep twice per 15 seconds after the preceding voice announcement.
The voice announcements always begin with the local time. When calling Washington, silence (only second ticks) may be heard for a few seconds before the next scheduled local time announcement. When calling Colorado, the local time announcement begins at the next 5 second interval, which means that the seconds portion of the times announced depends on the time of the call, and that there is a 1 in 3 chance, as shown in the table, of there being no beep at the top of each minute, which is what most watches and clocks require to synchronize.
| Seconds | Washington | Colorado (1 of 3 possibilities) |
|---|---|---|
| :00–:04 | Universal time 23 hours, 33 minutes, 5 seconds. | Mountain Daylight Time 17 hours, 33 minutes, 5 seconds. |
| :05–:09 | U.S. Naval Observatory Master Clock. At the tone, Eastern Daylight Time 19 hours, 33 minutes, 15 seconds |
Universal time 23 hours, 33 minutes, 10 seconds. |
| :10–:14 | U.S. Naval Observatory Master Clock. At the tone, Mountain Daylight Time 17 hours, 33 minutes, 20 seconds. |
|
| :15–:19 | Universal time 23 hours, 33 minutes, 20 seconds. | |
| :20–:24 | U.S. Naval Observatory Master Clock. At the tone, Eastern Daylight Time 19 hours, 33 minutes, 30 seconds. |
Universal time 23 hours, 33 minutes, 25 seconds. |
| :25–:29 | U.S. Naval Observatory Master Clock. At the tone, Mountain Daylight Time 17 hours, 33 minutes, 35 seconds. |
|
| :30–:34 | Universal time 23 hours, 33 minutes, 35 seconds. | |
| :35–:39 | U.S. Naval Observatory Master Clock. At the tone, Eastern Daylight Time 19 hours, 33 minutes, 45 seconds. |
Universal time 23 hours, 33 minutes, 40 seconds. |
| :40–:44 | U.S. Naval Observatory Master Clock. At the tone, Mountain Daylight Time 17 hours, 33 minutes, 50 seconds. |
|
| :45–:49 | Universal time 23 hours, 33 minutes, 50 seconds. | |
| :50–:54 | U.S. Naval Observatory Master Clock. At the tone, Eastern Daylight Time 19 hours, 34 minutes, exactly. |
Universal time 23 hours, 33 minutes, 55 seconds. |
| :55–:59 | U.S. Naval Observatory Master Clock. At the tone, |
The USNO also operates a modem time service, and provides time to the Global Positioning System.
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