How an Atomic Clock Really Works: Inside the HP 5061A Cesium Clock

CuriousMarc4 HN recommenders · 2020–2026
464K views · explainer · evergreen · Uploaded 2020-03-20

CuriousMarc powers up a vintage HP 5061A cesium beam clock and explains both the quantum principle and the HP implementation in detail. It is part of a longer atomic clock series.

HN calls it one of the best explanations of how atomic clocks actually work.

Watch on YouTube

4 comments from Hacker News

@kens2020 · in “Living Without Atomic Clocks (2016)”

CuriousMarc made a video last week where he uses a vintage HP 5061A atomic clock and explains how it works. It's interesting to see that atomic clocks aren't just some giant laboratory thing, but a product you could buy, even in the 1960s. [VIDEO]

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@somat2022 · in “Time is an illusion, Unix time doubly so”

CuriousMarc has an excellent episode on an atomic clock. [VIDEO] I like to pretend I can fix computers, this guy can actually fix computers, which is probably why I find his show so fascinating.

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@puzzledobserver2022 · in “The state of the art in amateur timekeeping (2003) [pdf]”

CuriousMarc uploaded a video to Youtube showing the startup procedure for an HP 5061A cesium clock [0]. They switch on the clock and compare it to a GPS reference. Seeing the abstract description realized in concrete terms through hot cesium tubes, phase locked loops, and Lissajous curves was really fascinating. [0] [VIDEO]

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@alnwlsn2026 · in “Atomic Clocks”

If you want to see how an actual application of this works, I've yet to see a description better than in CuriousMarc's HP 5061A series: [VIDEO]

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