[time-nuts] Re: Derivation of time from celestial sight

[Lux, Jim]

On 12/27/21 12:18 PM, Brent wrote:
> My understanding (and I could be wrong) is that one could derive 'stellar'
> time from a start sight/fix on polaris or another well tracked celestial
> object.  I was once told that early editions of Bowditch provided the
> process (for the moon I was told) although one of the relatively old
> edition's that I have doesn't provide it.

Occultation of stars by the Moon provides a "universal" time source 
(assuming you can see the Moon and stars). It was the competitor to 
Harrison's clock based approach to timekeeping for the measurement of 
longitude. For stars sufficiently far away, the Moon passes in front of 
it at the same time everywhere on Earth. There are some problems - the 
Moon has a rough edge, etc.  And, of course, you need accurate 
ephemerides for the Moon and accurate celestial position of the stars.

Observations of a star can only give you local time; you need two things 
moving at different speeds to get the time at a specific longitude.


>
> Some theodolite manufacturers provided attachments to aid the process (for
> the high zenith where a theodolite experiences reduced accuracy), and those
> attachments were dated and calibrated for their year of manufacture and
> came with tables for use in future years.
>
> That's about all I know or can find on the subject.  Can anyone here point
> me to any published literature?  Anyone have experience trying?  Any idea
> what type of accuracy can be expected?

There is a CD-ROM published by ION (Institute of Navigation) with 
hundreds of papers on such things.

https://www.ion.org/publications/upload/CelestialNavTOC.pdf

https://www.ion.org/publications/order-publications.cfm

$50 worth of reading on all manner of topics navigation and time related 
- Papers on "how Vikings navigated" "how Columbus navigated" (and papers 
refuting the theories in the previous papers, etc.)



>
> Got some new toys coming and need something to do with them....


And, of course, you can get yourself a copy of the Nautical Almanac and 
some sight reduction tables (get the airplane ones, not the ship ones) 
and do some celestial nav. You can make an artificial horizon with a pan 
of water at some distance, so you can sight your object of interest and 
the reflection at the same time.

>
> Brent
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.
>