Galaxy NGC 7217 from Paris... and a very strange guiding glitch


Dan_Paris
 

   Hi everyone,

NGC 7217 is a face-on spiral galaxy in Pegasus with a ring structure, located 50 millions l.y. from us. Its angular size is rather small (about 3') so a bit challenging for the 750mm focal length of my 8"  f/4 newtonian, but fortunately the ASI183mm has small pixels and my AP900 mount tracks very well (read below however...). The seeing was rather decent last night (2.3" FWHM after stacking).

 Link to the full-res picture:


http://www.astrosurf.com/uploads/monthly_2022_08/galaxie_NGC7217.jpg.12fd15518778372d36ccf1991acfbd84.jpg


Now some details about the glitch.

Right in the middle of a sub there was a huge and sudden jump in RA, resulting in a double image with two copies of the galaxy aligned with the RA axis : http://www.astrosurf.com/uploads/monthly_2022_08/double.jpg.f7f339b93832b59a35f319002cc22803.jpg

All the subs shot before this one had the galaxy in the center, while all the subs shot after had the galaxy in the corner!

I tried to understand what had happened during the night (I was sleeping) but did not find any satisfactory answer. The PHD2 log shows nothing. The imaging train with OAG was rigid, nothing sloppy or unscrewed. The mount was balanced accurately and  the clutches of the mount were tightened enough. The meridian flip had already occurred about one hour before. The mount was powered with its own battery (large capacity lifepo4).

I should mention that the setup was controlled by an ASIAIR and not by a PC, so it could be a bug of the Indi driver. But nothing like that ever happened before.

Any ideas ?

Have a nice day,

Dan

Technical data

200/800 custom Newtonian astrograph with Romano Zen optics and carbon fiber tube
AP900 CP4 mount on Losmandy HD tripod
TS 2.5" Riccardi-Wynne corrector

ASI183mm
ZWO LRGB filters
Guiding : ZWO OAG  + ASI120mm mini + AsiairV1
Luminance : 180 *60sec at -10°C
Chrominance : 30*60sec at -10°C for R and B channels, synthetic G
Darks, flats and synthetic biases
Conditions : Bortle 7/8 skies in Paris' suburbs (20km from the Eiffel tower), decent seeing (2.3" after stacking), last quarter moon.
Preprocessing and stacking with Siril, processing with Pixinsight and Rawtherapee


 

Hi Dan

are you using APCC?

I encountered something similar to this, and the source was I had turned on auto-meridian flip in the mount. That will "just flip the mount" even in the middle of an exposure.

I don't know if this is the case with yours, but it looks very similar

On Fri, Aug 19, 2022 at 6:06 AM Dan_Paris <danysra@...> wrote:
   Hi everyone,

NGC 7217 is a face-on spiral galaxy in Pegasus with a ring structure, located 50 millions l.y. from us. Its angular size is rather small (about 3') so a bit challenging for the 750mm focal length of my 8"  f/4 newtonian, but fortunately the ASI183mm has small pixels and my AP900 mount tracks very well (read below however...). The seeing was rather decent last night (2.3" FWHM after stacking).

 Link to the full-res picture:


http://www.astrosurf.com/uploads/monthly_2022_08/galaxie_NGC7217.jpg.12fd15518778372d36ccf1991acfbd84.jpg


Now some details about the glitch.

Right in the middle of a sub there was a huge and sudden jump in RA, resulting in a double image with two copies of the galaxy aligned with the RA axis : http://www.astrosurf.com/uploads/monthly_2022_08/double.jpg.f7f339b93832b59a35f319002cc22803.jpg

All the subs shot before this one had the galaxy in the center, while all the subs shot after had the galaxy in the corner!

I tried to understand what had happened during the night (I was sleeping) but did not find any satisfactory answer. The PHD2 log shows nothing. The imaging train with OAG was rigid, nothing sloppy or unscrewed. The mount was balanced accurately and  the clutches of the mount were tightened enough. The meridian flip had already occurred about one hour before. The mount was powered with its own battery (large capacity lifepo4).

I should mention that the setup was controlled by an ASIAIR and not by a PC, so it could be a bug of the Indi driver. But nothing like that ever happened before.

Any ideas ?

Have a nice day,

Dan

Technical data

200/800 custom Newtonian astrograph with Romano Zen optics and carbon fiber tube
AP900 CP4 mount on Losmandy HD tripod
TS 2.5" Riccardi-Wynne corrector

ASI183mm
ZWO LRGB filters
Guiding : ZWO OAG  + ASI120mm mini + AsiairV1
Luminance : 180 *60sec at -10°C
Chrominance : 30*60sec at -10°C for R and B channels, synthetic G
Darks, flats and synthetic biases
Conditions : Bortle 7/8 skies in Paris' suburbs (20km from the Eiffel tower), decent seeing (2.3" after stacking), last quarter moon.
Preprocessing and stacking with Siril, processing with Pixinsight and Rawtherapee




Dan_Paris
 

    Hi Brian,

Thanks for the suggestion.

I don't use APPC but an AISAIR (so the Indi driver). When it happened, meridian flip had already occurred half an hour before and all subs between meridian flip and this particular one were normal.


Roland Christen
 


Right in the middle of a sub there was a huge and sudden jump in RA
Generally when that happens it's the result of a guide star being lost and then the guide software latches onto a new guide star. Can happen after a cosmic ray hit which moves the scope to a new position, then tries to find the original guide star but latches onto a new one. Or passing cloud which obscures the guide star, causing a hunt for a new one. Or possibly a glitch in the dither software which moves the scope a large amount instead of a tiny amount.

Rolando

-----Original Message-----
From: Dan_Paris <danysra@...>
To: main@ap-gto.groups.io
Sent: Fri, Aug 19, 2022 8:06 am
Subject: [ap-gto] Galaxy NGC 7217 from Paris... and a very strange guiding glitch

   Hi everyone,

NGC 7217 is a face-on spiral galaxy in Pegasus with a ring structure, located 50 millions l.y. from us. Its angular size is rather small (about 3') so a bit challenging for the 750mm focal length of my 8"  f/4 newtonian, but fortunately the ASI183mm has small pixels and my AP900 mount tracks very well (read below however...). The seeing was rather decent last night (2.3" FWHM after stacking).

 Link to the full-res picture:

http://www.astrosurf.com/uploads/monthly_2022_08/galaxie_NGC7217.jpg.12fd15518778372d36ccf1991acfbd84.jpg


Now some details about the glitch.

Right in the middle of a sub there was a huge and sudden jump in RA, resulting in a double image with two copies of the galaxy aligned with the RA axis : http://www.astrosurf.com/uploads/monthly_2022_08/double.jpg.f7f339b93832b59a35f319002cc22803.jpg

All the subs shot before this one had the galaxy in the center, while all the subs shot after had the galaxy in the corner!

I tried to understand what had happened during the night (I was sleeping) but did not find any satisfactory answer. The PHD2 log shows nothing. The imaging train with OAG was rigid, nothing sloppy or unscrewed. The mount was balanced accurately and  the clutches of the mount were tightened enough. The meridian flip had already occurred about one hour before. The mount was powered with its own battery (large capacity lifepo4).

I should mention that the setup was controlled by an ASIAIR and not by a PC, so it could be a bug of the Indi driver. But nothing like that ever happened before.

Any ideas ?

Have a nice day,

Dan

Technical data
200/800 custom Newtonian astrograph with Romano Zen optics and carbon fiber tube
AP900 CP4 mount on Losmandy HD tripod
TS 2.5" Riccardi-Wynne corrector
ASI183mm
ZWO LRGB filters
Guiding : ZWO OAG  + ASI120mm mini + AsiairV1
Luminance : 180 *60sec at -10°C
Chrominance : 30*60sec at -10°C for R and B channels, synthetic G
Darks, flats and synthetic biases
Conditions : Bortle 7/8 skies in Paris' suburbs (20km from the Eiffel tower), decent seeing (2.3" after stacking), last quarter moon.
Preprocessing and stacking with Siril, processing with Pixinsight and Rawtherapee

--
Roland Christen
Astro-Physics


ap@CaptivePhotons.com
 

On Fri, Aug 19, 2022 at 01:37 PM, Roland Christen wrote:
Generally when that happens it's the result of a guide star being lost and then the guide software latches onto a new guide star.
Good imaging software will be doing plate solves in background and would recenter after the first off-position sub. I don't think the ASIAir has such capability though.  NINA for example does so with the "Center after drift" trigger, it examines each new sub in background (no delays) and if there is drift for whatever cause, it redoes a slew-and-center to bring it back and starts guiding again.

PHD2 (the real one, not sure on the limited version in ASIAir) also has a star mass change detection which can help determine a star may not be the right guide star, though I find it often more harm than good if there are transparency fluctuations at all. 

I've also seen PHD2 end up off location if it grabs a reflection or artifact and starts guiding on it for a while, it will merrily chase the (unmoving in frame while stars move) artifact until it disappears, or is reset.  There doesn't seem to be a sanity check in how far PHD2 will, on net, send corrections over time.

Linwood


 

uploading the guidelog would help here. It's just guessing otherwise


On Fri, Aug 19, 2022 at 10:37 AM Roland Christen via groups.io <chris1011=aol.com@groups.io> wrote:

Right in the middle of a sub there was a huge and sudden jump in RA
Generally when that happens it's the result of a guide star being lost and then the guide software latches onto a new guide star. Can happen after a cosmic ray hit which moves the scope to a new position, then tries to find the original guide star but latches onto a new one. Or passing cloud which obscures the guide star, causing a hunt for a new one. Or possibly a glitch in the dither software which moves the scope a large amount instead of a tiny amount.

Rolando

-----Original Message-----
From: Dan_Paris <danysra@...>
To: main@ap-gto.groups.io
Sent: Fri, Aug 19, 2022 8:06 am
Subject: [ap-gto] Galaxy NGC 7217 from Paris... and a very strange guiding glitch

   Hi everyone,

NGC 7217 is a face-on spiral galaxy in Pegasus with a ring structure, located 50 millions l.y. from us. Its angular size is rather small (about 3') so a bit challenging for the 750mm focal length of my 8"  f/4 newtonian, but fortunately the ASI183mm has small pixels and my AP900 mount tracks very well (read below however...). The seeing was rather decent last night (2.3" FWHM after stacking).

 Link to the full-res picture:

http://www.astrosurf.com/uploads/monthly_2022_08/galaxie_NGC7217.jpg.12fd15518778372d36ccf1991acfbd84.jpg


Now some details about the glitch.

Right in the middle of a sub there was a huge and sudden jump in RA, resulting in a double image with two copies of the galaxy aligned with the RA axis : http://www.astrosurf.com/uploads/monthly_2022_08/double.jpg.f7f339b93832b59a35f319002cc22803.jpg

All the subs shot before this one had the galaxy in the center, while all the subs shot after had the galaxy in the corner!

I tried to understand what had happened during the night (I was sleeping) but did not find any satisfactory answer. The PHD2 log shows nothing. The imaging train with OAG was rigid, nothing sloppy or unscrewed. The mount was balanced accurately and  the clutches of the mount were tightened enough. The meridian flip had already occurred about one hour before. The mount was powered with its own battery (large capacity lifepo4).

I should mention that the setup was controlled by an ASIAIR and not by a PC, so it could be a bug of the Indi driver. But nothing like that ever happened before.

Any ideas ?

Have a nice day,

Dan

Technical data
200/800 custom Newtonian astrograph with Romano Zen optics and carbon fiber tube
AP900 CP4 mount on Losmandy HD tripod
TS 2.5" Riccardi-Wynne corrector
ASI183mm
ZWO LRGB filters
Guiding : ZWO OAG  + ASI120mm mini + AsiairV1
Luminance : 180 *60sec at -10°C
Chrominance : 30*60sec at -10°C for R and B channels, synthetic G
Darks, flats and synthetic biases
Conditions : Bortle 7/8 skies in Paris' suburbs (20km from the Eiffel tower), decent seeing (2.3" after stacking), last quarter moon.
Preprocessing and stacking with Siril, processing with Pixinsight and Rawtherapee

--
Roland Christen
Astro-Physics




Andrea Lucchetti
 

I didn’t know this NINA setting, thank you!

Il giorno ven 19 ago 2022 alle 20:54 ap@... <ap@...> ha scritto:
On Fri, Aug 19, 2022 at 01:37 PM, Roland Christen wrote:
Generally when that happens it's the result of a guide star being lost and then the guide software latches onto a new guide star.
Good imaging software will be doing plate solves in background and would recenter after the first off-position sub. I don't think the ASIAir has such capability though.  NINA for example does so with the "Center after drift" trigger, it examines each new sub in background (no delays) and if there is drift for whatever cause, it redoes a slew-and-center to bring it back and starts guiding again.

PHD2 (the real one, not sure on the limited version in ASIAir) also has a star mass change detection which can help determine a star may not be the right guide star, though I find it often more harm than good if there are transparency fluctuations at all. 

I've also seen PHD2 end up off location if it grabs a reflection or artifact and starts guiding on it for a while, it will merrily chase the (unmoving in frame while stars move) artifact until it disappears, or is reset.  There doesn't seem to be a sanity check in how far PHD2 will, on net, send corrections over time.

Linwood


Joseph Beyer
 

Andrea, 

There’s a YouTube video by Patriot Astro (link below) in which he does a great job showing how to configure the center-after-drift utility so it keeps the object centered but does not conflict with the displacement introduced by dithering.  


Joe

On Aug 19, 2022, at 12:07 PM, Andrea Lucchetti <andlucchett@...> wrote:


I didn’t know this NINA setting, thank you!

Il giorno ven 19 ago 2022 alle 20:54 ap@... <ap@...> ha scritto:
On Fri, Aug 19, 2022 at 01:37 PM, Roland Christen wrote:
Generally when that happens it's the result of a guide star being lost and then the guide software latches onto a new guide star.
Good imaging software will be doing plate solves in background and would recenter after the first off-position sub. I don't think the ASIAir has such capability though.  NINA for example does so with the "Center after drift" trigger, it examines each new sub in background (no delays) and if there is drift for whatever cause, it redoes a slew-and-center to bring it back and starts guiding again.

PHD2 (the real one, not sure on the limited version in ASIAir) also has a star mass change detection which can help determine a star may not be the right guide star, though I find it often more harm than good if there are transparency fluctuations at all. 

I've also seen PHD2 end up off location if it grabs a reflection or artifact and starts guiding on it for a while, it will merrily chase the (unmoving in frame while stars move) artifact until it disappears, or is reset.  There doesn't seem to be a sanity check in how far PHD2 will, on net, send corrections over time.

Linwood


Andrea Lucchetti
 

Thanks a lot for sharing :-)

Il giorno ven 19 ago 2022 alle 23:38 Joseph Beyer <jcbeyer2001@...> ha scritto:
Andrea, 

There’s a YouTube video by Patriot Astro (link below) in which he does a great job showing how to configure the center-after-drift utility so it keeps the object centered but does not conflict with the displacement introduced by dithering.  


Joe

On Aug 19, 2022, at 12:07 PM, Andrea Lucchetti <andlucchett@...> wrote:


I didn’t know this NINA setting, thank you!

Il giorno ven 19 ago 2022 alle 20:54 ap@... <ap@...> ha scritto:
On Fri, Aug 19, 2022 at 01:37 PM, Roland Christen wrote:
Generally when that happens it's the result of a guide star being lost and then the guide software latches onto a new guide star.
Good imaging software will be doing plate solves in background and would recenter after the first off-position sub. I don't think the ASIAir has such capability though.  NINA for example does so with the "Center after drift" trigger, it examines each new sub in background (no delays) and if there is drift for whatever cause, it redoes a slew-and-center to bring it back and starts guiding again.

PHD2 (the real one, not sure on the limited version in ASIAir) also has a star mass change detection which can help determine a star may not be the right guide star, though I find it often more harm than good if there are transparency fluctuations at all. 

I've also seen PHD2 end up off location if it grabs a reflection or artifact and starts guiding on it for a while, it will merrily chase the (unmoving in frame while stars move) artifact until it disappears, or is reset.  There doesn't seem to be a sanity check in how far PHD2 will, on net, send corrections over time.

Linwood


Dan_Paris
 

Thanks Roland, Linwood and Brian for your suggestions.

Actually PHD2 recorded the event (see the screen capture). In my defence, I overlooked it as the time stamp for the frame was not correct (presumably daylight savings not handled properly by the ASIAIR).

Maybe some bird landed on the scope (but it would have been a fairly large one to shake an AP900...)


best regards,

Dan


 

yeah looks like a lost star event, not sure what happened there


On Fri, Aug 19, 2022 at 2:37 PM Dan_Paris <danysra@...> wrote:
Thanks Roland, Linwood and Brian for your suggestions.

Actually PHD2 recorded the event (see the screen capture). In my defence, I overlooked it as the time stamp for the frame was not correct (presumably daylight savings not handled properly by the ASIAIR).

Maybe some bird landed on the scope (but it would have been a fairly large one to shake an AP900...)


best regards,

Dan




ap@CaptivePhotons.com
 

On Fri, Aug 19, 2022 at 05:37 PM, Dan_Paris wrote:
Maybe some bird landed on the scope (but it would have been a fairly large one to shake an AP900...)
Here's my theory -- a mouse crawled up onto the mount somewhere.  A nearby barn owl, patrolling at night, noticed him, and struck capturing and carrying him off, but in doing so moved the mount.

Of course, a more mundane thing - I recently had two separate issues that caused problems for me, either of which I would have completely discounted. Long ago I did a lot of testing and knew so long as I didn't go (much) counterweight up, I would have no collisions.  Then one night I needed a new camera angle, and because of a short cable I turned the filter wheel down instead of up, not thinking about it.  It did not hit hard, but it hard enough to actual spin the wheel/camera to a completely different rotation at meridian flip, so half my subs were 10 degrees or so off. 

Problem #2 was I thought I had the pegasus with plenty of clearance, but there was one dec/ra combination where it dragged, not bad but enough to twist things and throw off my polar alignment by about 25-30'. 

My real point is, if the owl theory does not work for you, it may be worth taking a real hard look at the position everything was in at that hour, and see if there's a possibility something caught/turned/twisted/hit.   Murphy is active late at night especially when one is asleep.

Glad you at least confirmed the issue.  And if it is the owl, he did you a favor, the mouse was going to chew a wire. 

Linwood


Dan_Paris
 

   Hi Linwood,

I carefully checked for all possible cable snagging or collisions with the mount and did not find any (btw I never rotate the focuser precisely for this reason, the imaging train of my new astrograph is very close to the DEC axis).

This gives very strong support to the owl theory.

regards,

Dan


Howard Hedlund
 

Hi Dan,  You have some great replies above.  Guiding glitches can drive a person crazy.  (...short trip for some of us!) 
One of the first things to try to determine is whether the glitch is a random act caused by Murphy, gremlins, barn owls, etc., or a repeatable glitch that has an addressable cause and solution.  Murphy and his gang of accomplices will simply waste your time and make you tear your hair out.  
If you really want to dig into this, you need to start by isolating the event on any and all pertinent log files that may exist.  I don't know what sort of logging capabilities exist for your ASIAIR, but without concrete, time-stamped data, everything is speculation.  Just my 2¢!   HKH


Dan_Paris
 

Thanks Howard.

I  imaged  a nearby region of the sky yesterday (almost the same DEC) and nothing happened during the whole night so, fortunately, it was a one-time event (gremlin or else),

best regards,

Dan