[time-nuts] Pulsars, clocks, and time nuts (Jim Palfreyman)
djl at montana.com
Sun Apr 15 18:56:44 EDT 2018
On 2018-04-13 01:54, Tom Van Baak wrote:
> Amazing news... 1.2.3.
> 1) Many of you know that pulsars are weird astronomical sources of
> periodic signals. Some are so accurate that they rival atomic clocks
> for stability! True, but I don't have a 100 foot antenna at home so
> I'll take their word for it. Plus, you have to account for a myriad of
> PhD-level corrections: from earth's rotation to general relativity.
> And, like quartz or rubidium clocks, pulsars drift (as they gradually
> slow down). Precision timing is not easy. If you poke around the web
> you can find numerous articles describing their detection and
> measurement and exploring their use as reference clocks, both here and
> potentially for deep-space timekeeping.
> 2) If you do a lot of clock measurement at home then you know the dark
> side of working with precision clocks. There are signal quality
> issues, measurement resolution issues, reference stability
> limitations, offset, drift, phase jumps, frequency jumps, missed or
> extra cycles, glitches, etc. For example, quartz oscillators
> (depending on make / model / luck) can exhibit frequency jumps; i.e.,
> without warning they just change frequency without your permission.
> Ok, maybe not by a lot, but enough to notice; perhaps enough to cause
> trouble to any naive GPSDO PID algorithm that assumes steady state
> from the oscillator you thought was stable.
> 3) Now the exciting part! Fellow time-nut Jim Palfreyman studies
> pulsars. You've seen postings from him now and then over the years. It
> turns out Jim is the first person to catch a pulsar in the act of a
> frequency jump. After 3 years of continuous searching! This is really
> cool. Just amazing. You can't get more time nutty than this. And it
> just got published in Nature. It's a perfect never-give-up,
> i-eat-nanoseconds-for-breakfast, time nut thing to do. I am so
> To quote Jim:
> On December 12, 2016, at approximately 9:36pm at night, my phone
> goes off with a text message telling me that Vela had glitched. The
> automated process I had set up wasn't completely reliable - radio
> frequency interference (RFI) had been known to set it off in error.
> So sceptically I logged in, and ran the test again. It was genuine!
> The excitement was incredible and I stayed up all night analysing
> the data.
> What surfaced was quite surprising and not what was expected. Right
> as the glitch occurred, the pulsar missed a beat. It didn't pulse.
> Here is a very readable description of his discovery:
> And also the official Nature article with all the juicy, peer-reviewed
> So congratulations to Jim. I will think of him next time my 10811A
> quartz oscillator does a frequency jump or next time my 60 Hz mains
> frequency monitor skips a cycle...
> If you have comments or questions feel free to send them to Jim
> directly (see Cc: address). Perhaps he can summarize the questions and
> his answers in a posting to time-nuts soon.
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Dr. Don Latham
PO Box 404, Frenchtown, MT, 59834
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