Why did my AP1200 not flip? [pt 1]

[Mike Dodd]

Tonight's observing plan was M78 in H-a. My plan called for 15-minute exposures, and M78 transited at 23:27 local (04:27 UTC).

Fortunately, I decided to remotely watch the meridian flip.

Connecting to the observatory PC at 23:26, I was surprised to find the exposure still underway with three minutes remaining but only one minute to go until the transit. I thought ACP would not begin an exposure if it would not end until a couple of minutes before the transit

I was even more surprised when the exposure ended and ACP immediately began a new exposure. No flip took place.

I turned on the light in the observatory and took a look at the WebCam monitor. Sure enough, the telescope was pointing well past the meridian.

At this point, I aborted the plan, parked the scope, and shut down ACP.

I've never had any problem with ACP not doing the flip until tonight. In fact, this is exactly the same plan I used twice in the past two weeks, modified once for luminance and a second time for RGB. Tonight's only change specified the H-a filter and a 15-minute vs. 5-minute exposure. ACP correctly performed the meridian flip on the two previous runs.

Does anyone have any idea what happened? Is the longer exposure a factor? I was under the impression that ACP would stop tracking well in advance of a transit, regardless of exposure time.

I've attached my log from tonight's run. The key entries are:
04:14:40 (guider check OK, starting exposure)
04:30:03 Image finished
04:30:03 (autoguider still running...)
04:30:03 Imaging to M78 20091228 H-Alpha #006 900s Bin=1 PA=274 (W) -36c

The transit occurred at 04:27.


I consider myself very lucky that I decided to take a look right at the transit time. Had I gone to bed as planned, the scope would have crashed into the pier.

Thanks for any ideas on what happened.
-----
Mike

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com
http://NotWhatIVotedFor.com