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
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