Imaging under the pole


Tonight I’m contemplating trying to image a circumpolar object (Sh2-174). But this is quite unusual in that it will start on the west side of the pole, go underneath and cross back over onto the east side. Is SGP/AP Ascom driver smart enough to handle meridian flips like this?


It should be. But if not you’ll know immediately as it will try to flip right when you start. If that happens let us know and you can just turn off the meridian flip until your scope gets into a normal position. But there is handling specifically for this case.



I’ll take your word for it Jared. I’m trying to visualize how this will
work. The target will already be under the pole (alt 37deg) when I start,
and I’m not even sure which side of the pier the scope will be on at the
start. Unfortunately if it does try to flip right away I have no intention
of staying up until 1:00am when it crosses back into a more normal


You could try test it during the day and selecting any object inside circumpolar with Stellarium and see what it does.



True, that would at least give me an idea.


A properly implemented ASCOM driver should be OK. This is one of the cases I covered with my pointing state tester when we were worrying about what EQMOD was getting up to.

When the mount is pointing just West of the meridian the ASCOM pointing state should report PierEast (it uses the OTA position, not where it’s pointing) and this stays as PierEast as it crosses the meridian. A slew should do a big slew and change the pointing state.

Best to try Peter’s suggestion of trying it during the day. You can probably skip the solve and sync bit, just set up to collect images and see that an unsynced flip is done after the mount has tracked past the meridian.

All this assumes that the mount driver is ASCOM compliant and this is the sort of edge case that can catch them out.



I tried to do a simple test on this but there were too many parameters to
mess with so I’ll just give it a try and hope for the best. One thing
though, I slewed the scope to the approximate position in the sky my target
will be in. This means the scope was on the west side of the pier with the
counterweights pointed east. I also noted that there was no "time to flip"
in the bottom row indicator. Is that to be expected?

I would expect the Astro-Physics ASCOM driver to be implemented properly.