NIST Gaithersburg Atomic Clock Failure Causes -10ms Time Step on Internet Time Servers
By
dpcx
Reliable enough to start your morning with. Toast it again tomorrow.
Summary
On December 6, 2025, the primary atomic time source (a cesium beam atomic clock) at NIST's Gaithersburg campus failed, causing a -10 millisecond time step that affected multiple internet time servers. The failure impacted servers including time-a-g.nist.gov through time-f-g.nist.gov and ntp-d.nist.gov. Coincidentally, there were unexplained failures in other co-located monitoring and control resources, with server time-a-g becoming unavailable due to the incident.
Key quotes
· 4 pulledOn Saturday, 6 December 2025 at approximately 21:13 UTC, the atomic time source (a single cesium beam atomic clock) for all the internet time servers at the NIST Gaithersburg campus failed and exhibited a time step of approximately -10 ms.
The affected servers are: time-a-g.nist.gov time-b-g.nist.gov time-c-g.nist.gov time-d-g.nist.gov time-e-g.nist.gov time-f-g.nist.gov ntp-d.nist.gov (authenticated NTP only)
Coincidentally, there were unexplained failures in more than one co-located resource, including some used for monitoring and control.
The server time-a-g became unavailable due to the incident.
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