Re: AP 1600, Universal Time and Connecting to Auxiliary Astronomy Programs for Control

Jack Huerkamp


I got this link from George at Astro-Physics in which it says for a
dedicated observatory PC, to set its clock to UT along with the hand
controller being set to UT:

But it sounds like you are saying to set the observatory PC to local time
and the hand controller to UT, since SkyTools in my case is looking to the
computer time to locate targets.

If so, I will go to the observatory today and set the computer back to local
time, set SkyTools as well and see what happens.

Yours truly,


Jack Huerkamp
Jack's Astro Accessories, LLC
38388 Pine Street
Pearl River, LA 70452-5192
30.37N 89.76W

All of us get lost in the darkness.
Dreamers learn to steer by the stars.
..............Neil Peart

-----Original Message-----
From: <> On Behalf Of Dale Ghent
Sent: Tuesday, March 16, 2021 8:58 AM
Subject: Re: [ap-gto] AP 1600, Universal Time and Connecting to Auxiliary
Astronomy Programs for Control

So here's the deal: the mount CP deals only in UTC. All calculations
involving positions of objects in the sky are done UTC. For the purposes of
a mount's internal operations, UTC is the only thing that matters.

When you set the timezone on the keypad, you are essentially just
configuring the keypad's display and input of UTC time as local time. The
mount itself doesn't care that your offset from GMT is now -5 instead of -6.
That factors into none of its operations and calculations. What it does
factor into is how your keypad displays time, and how it converts time that
you input to and from UTC. The former - displaying the same time as your
local time - is just for convenience. The latter - inputting your local time
- is critical for the mount to derive the proper UTC time if you were to
program the mount's clock using the keypad. So if your local time is
18:45:00 and you were to program your mount's clock using the keypad today,
it would definitely need to know your current offset from GMT so that the
proper conversion to UTC can take place (that it would be 23:45:00 UTC).

The reason why you have to manually set the GMT offset in your keypad every
time DST begins or ends (or if you move to a different timezone altogether)
is because the keypad lacks its own timezone database that it can use to do
this automatically. You might ask "well how hard would it be for the keypad
to have one so that I don't need to do this". It's a valid question, but the
reasons are fairly basic. The timezone database is large and would occupy a
non-trivial amount of the keypad's very finite amount of static memory. It
also changes quite often as various countries and locales change their DST
observances or, in rare cases, which timezone(s) they are in. This would
demand that A-P issue several firmware updates a year in order to keep up
with these changes.

As for the computer and accessing the mount through the ASCOM driver, this
changes the situation in terms of mount time management. In this case, it is
presumed that your computer's clock is reasonably accurate as any modern OS
will automatically sync the computer's clock to an internet time source at
least once a week or more often, assuming it has internet access. There is a
setting in the A-P ASCOM driver to sync the computer's clock to the mount.
This should always be on if your computer's clock is reasonably accurate.
The ASCOM driver itself will then program the mount in UTC time directly in
this case. Despite your computer's timezone being set to US/Central, the OS
itself still operates in UTC internally. Because your OS does have a
maintained timezone database, it can do the display and input conversions
between your timezone and its internal clock, which runs in UTC.

So, the only reason why you would want to run your computer in UTC is if you
prefer viewing time that way. Even if you set the display of time on your PC
to be in your local timezone, the mount is still going to get programmed
with the proper time in UTC. It makes no difference to the mount.

As for the keypad, you can also just leave it with a timezone offset of 0 so
that it displays and takes input in UTC. However if you want it do display
and take time input in terms of your local time, you will need to manually
set the proper GMT offset whenever DST starts and ends.

On Mar 16, 2021, at 09:13, Jack Huerkamp <> wrote:

I use SkyTools 3 and SkyTools 4 to control my AP1600 mount using the ASCOM
driver. But every 6 months, I was having to switch the AP keypad from
standard time to daylight savings time and then back again 6 months later.
It was suggested to me to set the AP keypad to UT and also setting the
computer to UT to avoid have to mess with keypad settings every 6 months. I
did so and can control the mount using the keypad.

I then tried configuring my observatory location, but when I connected the
mount to SkyTools and did a slew to the Sun this afternoon, the scope tried
to aim into the ground on the southwest side of the pier. I need to know
how to set my location in SkyTools now that the mount and computer are set
to UT. I am in the Central US time zone.

I would appreciate feedback on this as I would hate to have to go back to
setting the computer and AP keypad to the current local time.

Yours truly,

Jack Huerkamp

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