What is this I've captured??!!

[rocketandroll]

Hi all

Ok... so I was imaging M51 up at Kelling Heath the last few days, just got back and have been stacking the data in DSS.

I was bemused as to why the final stacked image was always coming out very dark despite it being a total of an hour and a quarter of lights?

Anyway, I tried altering the settings and did a stack with the lights stacking method set to 'maximum'.

The finished product was brighter, but included a load of apparent satelite trails... and something REALLY strange.

I have not gone back to see if I can find the frame this appears in but it would seem to only be in one. I was imaging 40 sec subs with a 15 sec delay between subs.

I mean really... take a close look at the image below... and someone tell me what this is I've captured because it's freaking me out!

Top image is the full image, bottom one just the section middle left containing the eratic corkscrew trail.

I've not messed with the colour, it is bright red.

Anyone?!!

Ben

[Catanonia]

Bad sub where your guiding failed.

Find it and remove it befoe stacking. Always manually check your subs before stacking.

[rocketandroll]

Bad sub where your guiding failed.

Find it and remove it befoe stacking. Always manually check your subs before stacking.

well... A: it isn't guided, it was just left tracking, and B: if the tracking was affected on one frame, why would the only thing that appears in it be one red object and wouldn't it affect every star?

There were about 140 frames and I don't have any software to view them other than through DSS at the mo so checking every frame in detail would be a day or so's job... I will go find the offending frame, but I'm not sure a tracking error explains it?

Ben

[twotter]

ET stunt flying???

[mcrossley]

Looks like a hot red pixel showing the accuracy of your mounts tracking.

[ollypenrice]

Looks like a hot red pixel showing the accuracy of your mounts tracking.

So you reckon, in effect, a trace of periodic error and polar misalignment? Seems reasonable.

Olly

[mcrossley]

Exactly Olly. The slow drift of polar misalignment, with the PE superiposed on it. The 'old fashioned' way of plotting PE before we had autoguiding and the likes of PEMPro was to misalign your mount, and take a long exposure of a star to give this sort of trail. Because of the relatively short exposures here, when stacked they produce the inverse effect. If Ben stacked the frames without regard to the stars, then the stars would all show the same pattern and there would be one red dot.

[rocketandroll]

Yep... That'd explain it! Thanks guys :-)

Only thing it means is that DSS isn't picking up that hot pixel from my darks for some reason :-z

Cheers though!

Ben

[jam1e1]

hi ben i took some photos a few weeks ago caught a few red lines similar to yours - though not to corkscrew one. some of the lights i observed turned on/off intermittently hence with respect to corkscrew one, the short duration could be a plane switching lights on for a period then remaining off for rest of time in frame...

[mcrossley]

Ben, if you use one of the kappa sigma, or weighted average stacking methods in DSS it *should* largely eliminate both the hot pixel trail and the satellite streaks. You may have to play with the params a bit though to find what works with that set of images.

[rfdesigner]

What about the red arrows practicing at night?.. tail light while doing multiple barrel rolls ;-)

really.. hot pixel?.. how much drift was there between frames?

yup sigma clipping will take it out.. and the satellite trails.

Derek

[rocketandroll]

There actually wasn't an enormous amount of drift.

This imaging run lasted just over two hours, so the length of that red trail is how far the tracking drifted in two hours.

Not great, but not bad for a tripod standing in a muddy field, set up by a clueless newbie in about 10 minutes :-)

Ben