The Splinter Galaxy and a curly-wurly satellite

[lukebl]

Here is an image of the fine galaxy NGC5907, the Knife Edge or Splinter Galaxy high up in the constellation Draco.

Captured with my Omegon f/8 203mm RC. Unfortunately, the stars are slightly odd-shaped, so I am going to have to bite the bullet and tackle the nightmare of Ritchey-Chretien collimation. This, I gather from various threads, taxes even the most exprienced and technically-savvy practicioners out there, leading many to ditch their RC for something less challenging. Which is a shame, as I think this is a fine robustly-made scope, and designed for astro-imaging in the first place.

Atik 428ex, 43 x 300s exposures luminance. 20 x 60s RGB, binned 2x. Field of view 18.6 x 14 arcmin.

I noticed that one of the frames included a satellite with a curly-wurly trail. No idea how long it took to pass through the frame, but presumably it was tumbling and therefore of little practical use? Or was it something else?

[wxsatuser]

Never seen a trail like that, date and time of the that sub?

[lukebl]

6 minutes ago, wxsatuser said:

Never seen a trail like that, date and time of the that sub?

30th April 2019, 23.08 BST. I assume the time is the end of the capture. It's a shame that there's no way of telling how fast it was travelling across the frame, but it wasn't on the previous or subsequent frames.

[wxsatuser]

Iridium 5 passed right thru at 2305.

[Knight of Clear Skies]

Aircraft with a single wing-light in a continuous barrel roll?

That's a very strange trail. Constant brightness suggests the movement isn't caused by tumbling, and it would have to be a very large object to move that far at LEO altitudes. I'm wondering if the trail shape was caused by movement from the mount. Could the bright track from Iridium 5 have interfered with the guiding? It would have passed through the frame very quickly at that focal length, which could be why the stars look OK.

[lukebl]

24 minutes ago, wxsatuser said:

Iridium 5 passed right thru at 2305.

Interesting, although my Sky Safari Pro suggests that Iridium 5 was over 10 degrees away from NGC5907 at the time.

I thought that the wavy line might be due to mount errors, but other satellite trails during the same session are stright lines.

[wxsatuser]

Sat is going left to right diagonally.

[wxsatuser]

Have found another image of Iridium 5 but not as good as yours.

https://catchtheiridium.com/gallery/?contest=photo-detail&photo_id=1745

[lukebl]

11 minutes ago, wxsatuser said:

Sat is going left to right diagonally.

 

Ok, I'll take your word for it!

However, Skysafari Pro definitely has it in a different location to your Stellarium image. But, given the timing I guess that's what it must be.

[Astroscot2]

If the satellite was passing through the field very slowly, the oscillation effect could be your guiding rocking back and forth ??

[wxsatuser]

1 hour ago, lukebl said:

Ok, I'll take your word for it!

However, Skysafari Pro definitely has it in a different location to your Stellarium image. But, given the timing I guess that's what it must be.

Presume the keps are up to date?

[Jkulin]

6 hours ago, lukebl said:

Unfortunately, the stars are slightly odd-shaped, so I am going to have to bite the bullet and tackle the nightmare of Ritchey-Chretien collimation

Have you got a dew heater switched on full blast on the mirrors as this will give this effect as I had this problem, now I only gingerly apply the heater power and no more odd shaped stars

[Laurin Dave]

Just seen a thread on CN where the OP had a cooling fan vibration issue on their ASI1600 that was causing odd shaped stars and curly wurly satellite trail.  Maybe same issue here. 

[lukebl]

Thanks for the responses.

I don't have a dew heater, so that can't be cause of the odd stars, and I also don't have a cooling fan so that couldn't cause the odd satellite trail. Also, the trail seems too regular to be simple oscillation of the guiding, especially as other satellite trails are perfectly linear. A wobbly satellite seems to be the only possibility.

[Knight of Clear Skies]

15 minutes ago, lukebl said:

A wobbly satellite seems to be the only possibility.

It would be possible to work out the image scale at orbital altitudes. I suspect it's not possible for an object to move that far from side-to-side, the energy to do so would need to come from somewhere. I'm fairly sure that whatever is happening it's going on at the mount end.

[lukebl]

32 minutes ago, Knight of Clear Skies said:

....I'm fairly sure that whatever is happening it's going on at the mount end.

That's a bit worrying, but wouldn't that size of oscillation result in large bloated stars. There are small stars in the image which are smaller that the extent of the oscillation. Surely they would appear at least as big as the oscillation. Plus the fact that other satellite trails appear straight, like this much-enlarged extract from another frame?

[Laurin Dave]

I was meaning the cooling fan on your 428ex...  this was the thread...  ASI071 not ASI1600 https://www.cloudynights.com/topic/613410-star-ovalization-with-asi071mcp-psu-or-fan-issue/

[lukebl]

40 minutes ago, Laurin Dave said:

I was meaning the cooling fan on your 428ex...  this was the thread...  ASI071 not ASI1600 https://www.cloudynights.com/topic/613410-star-ovalization-with-asi071mcp-psu-or-fan-issue/

That's very worrying. The Atik wasn't cheap, and it's not much use if the fan wobbles!

[Knight of Clear Skies]

59 minutes ago, lukebl said:

That's a bit worrying, but wouldn't that size of oscillation result in large bloated stars.

Possibly not, if the oscillation is only happening while the bright satellite crosses the frame, which is why I wondered if its appearance had interfered with the guiding somehow. Or perhaps the satellite passage coincided with a brief period of oscillation. The satellite is much brighter than any of the stars in frame.

It is puzzling and there is always a chance we are missing something. 

[tooth_dr]

I think I have captured 3 in total over the past 2 years.  The oscillations are as tight though, but it was very slow, crossed through 3 x 300s subs in a row.