Re: [LEAPSECS] Types of time

From: Roger Stapleton <jrs_at_st-andrews.ac.uk>
Date: Fri, 8 Sep 2000 13:08:04 +0100 (BST)

On Fri, 8 Sep 2000, Ken Pizzini wrote:

> There is a use for astronomical time, which (it seems to me) would be
> better served by a sidereal clock (whether actual or mean) than a
> mean-solar-day based UT1, so keeping |UTC-UT1| < 0.9s doesn't seem
> like something that is helping the astronomical community any.

I have a real problem that this discussion may affect. Just now I have the
job of rewriting the program that does encoder readout and position
display for our 1m class telescope. For this I need local siderial time
(LST) to 1sec accuracy (the encoders set the accuracy limit - they are a
few years old).

At present this is no problem. I know the lat/long of the telescope so,
given "clock on the wall time" and date I can compute LST. My time/date
comes from either a digital clock with an MSF receiver in it, or from the
network. Both of these give me UTC - ok, MSF gives me UTC+1 in summer, but
it also has a 1-bit flag that tells me it is doing this - with sufficient
accuracy.

Since I only need 1sec accuracy, leap seconds do not upset an observing
run, so I can ignore this size of discontinuity. But if leapseconds did
not happen then I need to know what the offset is from network/MSF time to
UTC. I also need to be able to get this information without the observer
having to type it in, or take other action.

Ok, now we have a real (if small) problem to kick round the
discussion - and I can stop work on it until we have an answer ;-)

                Roger

------------------------------------------------------------------------
Roger Stapleton jrs_at_st-and.ac.uk
University of St.Andrews, School of Physics & Astronomy
North Haugh, St.Andrews, Fife. KY16 9SS
Phone 01334-463141 Fax 01334-463104
Received on Fri Sep 08 2000 - 05:18:33 PDT