Editing United States Naval Observatory (section)

==Time service==
{{see also|WWV (radio station)|label1=Radio stations WWV, WWVH, and WWVB – NIST time & frequency broadcast}}
[[Image:Usno-mc.jpg|thumb|right|Atomic clock ensemble at the U.S. Naval Observatory]]
The U.S. Naval Observatory operates two "Master Clock" facilities, one in Washington, DC, and the other at [[Schriever Space Force Base|Schriever SFB]] near [[Colorado Springs, Colorado|Colorado Springs, CO]].
* The primary facility, in Washington, D.C. maintains 57&nbsp;[[Hewlett-Packard|HP]]/[[Agilent Technologies|Agilent]]/[[Symmetricom]] 5071A-001 high performance [[cesium]] atomic clocks and 24&nbsp;[[hydrogen maser]]s.<ref name="matsakis2010"/>
* The alternate facility, at [[Schriever Space Force Base]], maintains 12&nbsp;cesium clocks and 3&nbsp;masers.<ref name="matsakis2010">{{cite report |first=Demetrios |last=Matsakis |date=2010-09-20 |title=Report from the U.S. Naval Observatory |collaboration=Civil GPS Service Interface Committee |publisher=[[United States Coast Guard]] |url=http://www.navcen.uscg.gov/pdf/cgsicMeetings/50/%5B15%5DUSNOreport_matsakis_sep2010.pdf |archive-url=https://web.archive.org/web/20110614023137/http://www.navcen.uscg.gov/pdf/cgsicMeetings/50/%5B15%5DUSNOreport_matsakis_sep2010.pdf |archive-date=2011-06-14 |url-status=live |access-date=2010-10-31}}</ref>

The observatory also operates four<ref>{{cite press release |url=http://www.usno.navy.mil/USNO/tours-events/u.s.-naval-observatory-declares-full-operational-capability-for-rubidium-fountain-clocks |title=U.S. Naval Observatory declares full operational capability for rubidium fountain clocks |date= |access-date=2014-04-10 |archive-date=2015-09-22 |archive-url=https://web.archive.org/web/20150922043917/http://www.usno.navy.mil/USNO/tours-events/u.s.-naval-observatory-declares-full-operational-capability-for-rubidium-fountain-clocks |url-status=dead }}</ref> [[rubidium]] [[atomic fountain]] clocks, which have a stability reaching 7{{e|-16}}.<ref>{{cite report |title=Initial Evaluation of the USNO Rubidium Fountain |date=2006-01-27 |publisher=[[United States Navy]] |department=U.S. Naval Observatory |url=http://ad.usno.navy.mil/edboard/060127.pdf |access-date=2010-11-17 |url-status=dead |archive-url=https://web.archive.org/web/20110615095955/http://ad.usno.navy.mil/edboard/060127.pdf |archive-date=2011-06-15}}</ref> The observatory plans to build several more of this type for use at its two facilities.<ref name="matsakis2010"/>

The clocks used for the USNO timescale are kept in 19&nbsp;environmental chambers, whose temperatures are kept constant to within 0.1°C. The relative humidities are kept constant in all maser, and most cesiums enclosures, to within 1%. Time-scale management only uses the clocks in Washington, DC, and of those, preferentially uses the clocks that currently conform reliably to the time reports of the majority. It is the combined 'vote' of the ensemble that constitutes the otherwise-fictitious "Master Clock". The time-scale computations on 7&nbsp;June 2007 weighted 70 of the clocks into the standard.<ref name="matsakis2010"/>

[[File:US Naval Observatory Master Clock.jpg|thumb|US Naval Observatory outside display of the [[master clock]] time]]
The U.S. Naval Observatory provides public time service via 26&nbsp;[[Network Time Protocol|NTP]]<ref name="matsakis2010"/> servers on the public [[Internet]],<ref>{{cite web |title=USNO Network Time Servers |website=tycho.usno.navy.mil |url=http://tycho.usno.navy.mil/ntp.html |access-date=2011-07-27 |archive-date=2006-01-16 |archive-url=https://web.archive.org/web/20060116054653/http://tycho.usno.navy.mil/ntp.html |url-status=dead }}</ref> and via telephone voice announcements:<ref>{{cite web |title=Telephone Time |url=https://www.cnmoc.usff.navy.mil/Our-Commands/United-States-Naval-Observatory/Precise-Time-Department/Telephone-Time/ |access-date=2023-07-01 |archive-date=2023-07-01 |archive-url=https://web.archive.org/web/20230701173820/https://www.cnmoc.usff.navy.mil/Our-Commands/United-States-Naval-Observatory/Precise-Time-Department/Telephone-Time/ |url-status=live }}</ref>
* +1 202 762-1401 (Washington, DC)
* +1 202 762-1069 (Washington, DC)
* +1 719 567-6742 (Colorado Springs, CO)
The voice of actor Fred Covington (1928–1993)<ref>{{cite magazine |title=The timekeeper behind America's master clock |date=5 December 2012 |magazine=[[Washingtonian (magazine)|Washingtonian]] |url=https://www.washingtonian.com/2012/12/05/the-timekeeper-behind-americas-master-clock/ |access-date=7 April 2021 |archive-date=16 April 2021 |archive-url=https://web.archive.org/web/20210416123152/https://www.washingtonian.com/2012/12/05/the-timekeeper-behind-americas-master-clock/ |url-status=live }}</ref> has been announcing the USNO time since 1978.<ref>{{cite news |title=Keeping time by rubidium at the Naval Observatory |publisher=[[NPR]] |url=https://www.npr.org/2014/07/06/329154831/keeping-time-by-rubidium-at-the-naval-observatory |access-date=2015-03-11 |archive-date=2015-03-29 |archive-url=https://web.archive.org/web/20150329005351/http://www.npr.org/2014/07/06/329154831/keeping-time-by-rubidium-at-the-naval-observatory |url-status=live }}</ref>

The voice announcements always begin with the local time (daylight or standard), and include a background of 1&nbsp;second ticks. Local time announcements are made on the minute, and 15, 30, and 45&nbsp;seconds after the minute. [[Coordinated Universal Time]] (UTC) is announced 5&nbsp;seconds after the local time.<ref>{{cite web |title=Telephone Time |series=Naval Oceanography Portal |website=www.usno.navy.mil |url=https://www.usno.navy.mil/USNO/time/telephone-time |access-date=2021-01-17 |archive-date=2021-01-22 |archive-url=https://web.archive.org/web/20210122024611/https://www.usno.navy.mil/USNO/time/telephone-time |url-status=dead }}</ref> Upon connecting, only the second-marking ticks are heard for the few seconds before the next scheduled local time announcement

The USNO also operates a modem time service,<ref>{{cite web |url=http://tycho.usno.navy.mil/modem_time.html |title=USNO Master Clock via Modem |publisher=Tycho.usno.navy.mil |access-date=2011-07-27 |archive-date=2017-12-27 |archive-url=https://web.archive.org/web/20171227233738/http://tycho.usno.navy.mil/modem_time.html |url-status=dead }}</ref> and provides time to the Global Positioning System.