[LEAPSECS] leapseconds, converting between GPS time (week, second) and UTC

[Rob Seaman]

Pointing telescopes is only one astronomical use case, and comes with
many caveats as Steve suggests, including the need for a pointing model
to correct for flexure and temperature terms in the telescope,
instrument, and optics. Telescopes also come in many flavors and what's
true for radar applications is not an issue for optical/IR or xrays.
Leap second handling for astronomy was first discussed here 15 years ago
or more, but seems orthogonal to the original question:

> /I'll probably test it for the cases I'm interested in (Ruby, Python,
> Excel, Matlab, Octave), but if someone else has already done it, then
> I've got something to cross check against./

I would add MySQL/MariaDB and PostgreSQL, as well as TCL and C/C++ to
that list. If JPL were to support libraries implementing some useful
subset of timekeeping utilities under a smorgasbord of such languages,
members of this list would undoubtedly be delighted to cross-check the
results and put them to good use (via GitHub or what have you).

That said, it isn't clear what the original use case involves. Something
about spacecraft using GPS week numbers and ground systems using UTC?
But what do you need to do exactly? And is this onboard or on the ground?

Rob

--

On 1/15/19 1:46 PM, Steve Allen wrote:
> On Tue 2019-01-15T11:49:00-0800 Tom Van Baak hath writ:
>> Still, I bet more astronomers use Python than Excel to point
>> telescopes.  How do you handle the lack of leap second support in
>> Python?
> I can't say that anyone uses Python to point a telescope, but it
> does not matter if they do.  See preprint 678 from the 2011
> Future of UTC meeting proceedings
> http://hanksville.org/futureofutc/2011/preprints/index.html
> In short:
>
> 19th century telescopes point by moving them manually.
> 20th century telescopes are built like battleships and raw pointing is
> only a bit more accurate than steering a battleship.
> 21st century telescopes are robotic, but they still have flexure and
> slop that requires them to update their pointing models regularly, and
> those slop parameters easily soak up one second.
>
> The APF telescope at Lick is robotic.  Its pointing system produces a
> time mismatch alarm whenever there is a leap second and requires a
> reboot.  At the most recent summer leap second we were able to see a
> star before and after, and there was a jump in the centering.  The
> software chose a different offset in the pointing for that night.
>
> --
> 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
> _______________________________________________
> LEAPSECS mailing list
> LEAPSECS at leapsecond.com
> https://pairlist6.pair.net/mailman/listinfo/leapsecs
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://pairlist6.pair.net/pipermail/leapsecs/attachments/20190115/9a506f0a/attachment.html>