[time-nuts] Re Danjon Astrolabe

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Sep 26 09:45:48 EDT 2006

> In article <44D8C0BB.1030608 at pacific.net <https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>>, Brooke Clarke
> <brooke at pacific.net <https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>> writes
> >/Hi Geoff:
> />/
> />/Thanks for the reference to "Geodesy".  Do you know if the first edition 
> />/has the Danjon information?
> />/I ask because the second editions are rather pricey and the 3rd and 4th 
> />/are not available at all.
> />/Could someone on this list make a copy of the Danjon section?
> />/
> /I'm quoting from memory about the workings of the Danjon Astrolabe - the
> book was borrowed from my local library, and I don't remember which
> edition it was. 
> Nor can I quote chapter and verse, I fear - although I will attempt to
> re-borrow the book, and copy the relevant section. Later this week, I
> hope.
> AFAIR, the discussion was of the workings of various instruments for
> determination of time from the stars, together with ways to mitigate the
> systematic errors in each instrument. "Personal equation" figured large
> in all this, which is why the PZT was preferred.
> -- 
> Geoff Powell

The explanation of the operation of the Danjon Astrolabe is somewhat 
There was a motor driven optical mechanism that was used to keep the 2 
stellar images superimposed for some time so that a sequence of 
observations could be taken on a single star.
This significantly reduced the personal equation on the measurements 
obtained with this impersonal version of the astrolabe.

I remember a book on Astrometry (sorry cant remember the title) that had 
detailed cross sections of the astrolabe together with a very detailed 
description of how it worked.
A modified version of the Dajon Astrolabe is currently in use at 
Santiago Chile for Solar astrometry.


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