[time-nuts] Calculating sidereal time

[Didier Juges]

Actually not a specific requirement. I made (and am in the process of
making a new batch of) an assembled kit which is used to monitor the data
stream from a Trimble Thunderbolt GPSDO and display time and vital
information on a small LCD display.

A long time ago, Brooke Clarke, on this list asked if I could make it
display sidereal time. I had no idea what it was so I researched it and
found out I needed to be able to process double precision calculations,
which the original 8 bit microcontroller was totally incapable of.

So I set this aside but I recently came across an inexpensive ARM chip and
decided to make a new version of my monitor with it. The toolchain is
excellent and supports double precision so I decided to fullfil Brooke's
request, who by now has probably lost interest in it but for the fun of it
and to learn something.

So while I understand sidereal time is used by astronomers, I am not one so
I have no personal practical use for it, which has the advantage of setting
the bar pretty low to decide when I am done :) That said, I am open to
suggestions to actually make it more useful if possible.

It is so easy to load an app in your phone if you actually need sidereal
time that I do not believe my kit will be used for that purpose but it was
an interesting exercise for me and I am glad it is working.

I learned quite a bit and discovered, through your postings and the
associated links how complex that subject actually is.

I love this list.

Didier KO4BB


On Sat, Jan 19, 2019, 8:01 PM Steve Allen <sla at ucolick.org wrote:

> On Sat 2019-01-19T12:15:28-0800 Steve Allen hath writ:
> > The most expedient place to find them are roughly pages B7 to B12 in a
> > current Astronomical Almanac.  See for example
> >
> https://babel.hathitrust.org/cgi/pt?id=uc1.31822038913307;view=1up;seq=116
>
> Emphasizing one point, it has always been important to use expressions
> for GMST and such things which are designed for use in the same
> reference frame as the star catalog.  Current star catalogs do not use
> an equinox as any kind of reference point, therefore any expression
> for GMST does not simply correspond to the longitude-like coordinate
> of a current star catalog.  GMST now coresponds to a new fictitious
> point in the sky which is defined with much more complexity than in
> the old days.
>
> What exactly is the intended use case for this project?
>
> --
> Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
> UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat
> +36.99855
> 1156 High Street               Voice: +1 831 459 3046         Lng
> -122.06015
> Santa Cruz, CA 95064           https://www.ucolick.org/~sla/  Hgt +250 m
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>