LST discrepancy?

[Rusted]

Hi,

I am still trying to pin down why my AWR/ASCOM Goto slews are ALWAYS inaccurate when using C-Du-C.  [Skychart]

My observatory site coordinates are set to within one second in both Latitude and Longitude on the AWR IH2 paddle.

My site location in C-Du_C is also precisely set to the second. I have set C-Du-C time to System time with 10 seconds refresh.

Now comes the hard part:

If I hover the cursor over the Meridian on the C-Du-C chart I think I should get LST. [Local Sidereal Time]
Instead I get a difference of -2 minutes compared to AWR's LST.

An online LST calculator also shows a discrepancy of exactly -2 minutes compared to AWR.  Local Sidereal Time Clock
But it also agrees exactly with C-Du-C. 

In fact have to change the longitude setting in the LST calculator [link above] by 0.62° to match the LST indicated on the AWR paddle.

So, which of these three LSTs is right?

A: The  two which agree?

B: Or the one which doesn't?

😄 None of them and I'm doing it all wrong?

Thanks

[AKB]

Commiserations.

Strangely enough, I suffered the same problem through much of the previous imaging season with ASCOM, an Avalon mount controlled by StarGO, and Stellarium running on an Eagle 2 observatory computer.  It was not always this way, but somewhere along the line it started happening.  Checked times and coordinates in all possible places a dozen times.

I never got to the root cause, but in the course of reassembling everything for the new season I've started with a clean slate and latest software/firmware versions of everything, and now things are spot on.

I hesitate to suggest this as a solution, because it was a real pain, but perhaps less than the pain of having inaccurate Goto.  Also, YMMV and it may not fix the problem.  Experience shows, though, that in this situation the problem is not where you are looking for it, so the nuclear option might be the fastest way. 

Good Luck

Tony

Edited September 24, 2019 by AKB

[Dr_Ju_ju]

If you are plate solving, does it matter ??  as any discrepancy in location will be ironed out....

[Rusted]

Thanks Tony.

I monitor the ASCOM support group and they regularly warn against re-installing.
I did ASCOM Diagnostics and Conformance scans yesterday to no avail.
No problems found and I have all the latest versions.

AWR repeated the advice to ensure I have the correct site location.
I confirmed my location with three different aerial photography services to the centre of my pier.
Decided averaging and rounding to a tenth of a second just wasn't good enough.
So I used Google Earth which shows my pier inside my observatory to a hundredth of a second.

Thanks Julian, but I have never knowingly done any plate solving.
I'm more of a click and Goto sort of chap.
Just finding the Moon and Sun are presently much too difficult for ASCOM/AWR/CduC.
Perhaps they are simply not team players?

[andrew s]

Is the time set in the AWR hand set correct.  Local time is also used to calculate LST

Regards Andrew 

[Rusted]

Hi Andrew,

AWR maintains an internal quartz clock crystal. You can't override it.

All you can do is set your precise location and it will/should calculate LST from the RTC.

That said I had to change the summer time settings when AWR disagreed with several online LST calculators.
But that was a straight one hour difference. Not just two minutes.
I'm on the CET band in Europe.  One hour forwards of Gravely Blighted's clock time.

[andrew s]

35 minutes ago, Rusted said:

Hi Andrew,

AWR maintains an internal quartz clock crystal. You can't override it.

All you can do is set your precise location and it will/should calculate LST from the RTC.

That said I had to change the summer time settings when AWR disagreed with several online LST calculators.
But that was a straight one hour difference. Not just two minutes.
I'm on the CET band in Europe.  One hour forwards of Gravely Blighted's clock time.

Yes but you can set it or at least you could in my day when I had one. If you have never set it I am sure it will be out by now.

Regards Andrew 

[Rusted]

Thanks Andrew. Is two years from new long enough to gain two minutes?
I am off to reduce LST by two minutes to see if that finally brings AWR to heel on Gotos. 
Earlier rain has given way to sunny periods. So I'm off to play.

[andrew s]

10 minutes ago, Rusted said:

Thanks Andrew. Is two years from new long enough to gain two minutes?
I am off to reduce LST by two minutes to see if that finally brings AWR to heel on Gotos. 
Earlier rain has given way to sunny periods. So I'm off to play.

Just look at what it says the UCT time is compared to your computer both could be out. The LST app will have used the computer time so it will appear right.

Regards Andrew 

Edited September 24, 2019 by andrew s

[Rusted]

Aha! The Zanzibar Fallacy.

[andrew s]

Did you get to the bottom of this?

Regards Andrew 

[Rusted]

In a sense. I paid for the latest ASCOM-AWR driver. 7.2.

So far so good. Though without any real targets to test it properly.

At least the unstable time and location coordinates didn't change randomly.

Since they are all interconnected it was inevitable mayhem would ensue.

Mostly solid cloud since then.