Ra/dec/lst

[Jim McMillan]

Hi Bob,

I've never worried about any of this before, and probaby shouldn't worry about it now, but...

Should I expect to see the same numbers for RA/DEC/LST on the ACP control panel and the AP V2 driver control panel? The pointing corrector is active. Pointing works great. I have no operating problems at all.

I'm including a screen shot...which shows different numbers. Should I care?

Jim

[Dick Berg]

Jim,

You know that you can also connect SNP to the ACP hub and track the telescope on the SNP map, and of course you have the MaxIm readouts as well. So there are four screens you could compare! But then, you're not going to worry about this anymore, are you... ;-)

From the two screens, I think the worrysome difference is the difference(s) in RA/Dec between ACP and AP. The difference is not due to JNow vs J2000 - which is somewhere around 40 seconds for RA (at this position in the sky) and 3 arcmin in Dec. interestingly, and coincidentally I'm sure, the difference in RA is 1m 24s and the difference in Dec is 1' 24".

There's a four second difference in the LSTs shown but that won't account for these differences. I presume your site coordinates are the same (including elevation), and that the mount doesn't know anything by name about the object you're looking at.

I'd bet there's a sign error in some equation along the way, but I couldn't guess whether it's ACP, SNP or AP's issue.

[Jim McMillan]

Hi Dick,

Thanks for the input.

The screenshot was taken while the pointing corrector was active. Once deactivated, RA and DEC as reported by ACP and the driver were the same (as was the local time). Interestingly, LST stayed 4 seconds apart. I don't know why.

I've triple-checked the location data in the driver, mount, SNP, and ACP. It is the same. As I said, I've given up trying to figure this out. The transit point in SNP and the calculated flip point in ACP/mount are just different - and that's the way it's supposed to be, I guess!?!

Jim

[Bob Denny]

Jim --

As you found, with the pointing corrector active, the coordinates displayed in ACP are the corrected ones not the raw ones coming from the scope. The 4 sec difference is probably a difference in the computer and scope clocks. ACP reports LST based on the computer clock (long story, and one of those things I did years ago before I stopped trying to make up for bad mounts).