michael.h.f.wilkinson

They may have been taken through slightly different filters. There seems to be more continuum emission in the lower one, especially in the outer reaches of M31

What I imagine could be done is to use a broader band filter (one or more) to to estimate the background continuum contribution (e.g. by scaling it to the correct level using least-absolute-deviates linear fitting) That should work reasonably well. Ideally you would block the O-III line, but even without that, estimating the background continuum contribution boils down to solving a large set of linear equations.

I have spoken to a couple of colleagues in the astronomy department, and they think it is a legitimate detection. The fact that the same structure appears in data from different scopes in the same location is highly unlikely to be the result of a processing artefact. There have been more such detections (think of the Squid Nebula, and several very faint PNs) in O-III by amateurs willing to spend loads of time on a single target. It does of course help if others can confirm the detection.

I have three variants of the ASI183: an ASI183MC (non-cooled), which I now only use for planetary and lunar imaging, an ASI183MC-Pro, which I now use for DSO OSC work, and an ASI183MM-Pro for narrowband/luminance shooting. The latter two are way better for DSO work, not just for reducing noise, but in particular due to the fact that I can simply always shoot at the same temperature of the chip, allowing me to use the same darks every time, or shoot darks at any time I like, rather than at the start or end of each imaging session, which I had to do with the ASI183MC. That doesn't mean the non-cooled camera is bad, given the results I was getting on the Meade SN-6 6" F/5 Schmidt-Newton. The M101 below represents just over 4 hours of data from a Bortle 4-5 site.

For solar, the only diagonal I use is a Herschel wedge. Both my Ca-K module and H-alpha filter system are straight-through types.

See report here:

Set up the Coronado SolarMax-II 60 mm again over lunch. Loads of activity on the disk. The big AR on the lower left of the disk (south-west of the centre, due to the diagonal in use) showed a lot of bright plage, apart from the spots themselves. Several long thin filaments snaked across the disk, in particular in the southern hemisphere. Quite a few smaller proms showed up as well, with one of the brighter ones at the 9 o'clock position. North of that at about 10 o'clock there were two proms: an upper one which was fairly elongated and firmly attached, and a much longer one, detached from the disk, pointing almost due north (slightly westwards). I guess it must be around 100,000 km long, perhaps longer. Really impressive. It might of course still be attached to the disk by some thin strands of plasma, but there was nothing that I could see.

OK, here goes. The Celestron GP-C8 has been my visual, planetary and lunar workhorse for over 27 years, so it is certainly a hugely loved scope. It has captured my best lunar and planetary images, and my first total eclipse, captured all of the supernovae I have seen, and shown the best visual planetary detail of any scope I have used (including a TEC-140, but that was under atrocious seeing conditions). The other Cat in my collection is the Meade SN6 6" F/5 Schmidt-Newton, the OTA of which set me back no less than EUR 165 (with better focuser, and better flocking than the stock tube). It has been such a great wide-field instrument, providing a whopping 3.3 degrees FOV at 24.5x with the mighty Nagler 31mm T5 (a.k.a. the "Panzerfaust"). It is great for comet hunting and a lovely DSO imaging scope. No slouch on planets either, but the C8 beats it. My first proper scope was a home-made 6"F/8 Newton, in a Dobson-like fork mount. I made it when I was 17 (bought the mirrors, 1/10 lambda according to the specs). With its small secondary obstruction this was a real planet killer, but also showed me many DSOs beautifully. I later rebuilt it with an octagonal plywood tube, and much better flocking and baffling than before, improving the contrast a lot. I also replace the rather wobbly fork mount. Then there is the APM 80 mm F/6 APO triplet, which functions as my main solar scope, grab-and-go wide-field scope, and DSO imaging scope for larger targets. I have more scopes, also well loved, but the foursome here are special, and I still have three out of these four.

On average the wavefront is flat, is what I claimed. The idea is that there is no systematic deviation from flat, it is just a series of random wobbles, equally likely to go up or down at any point along the front. During really bad seeing there may not a single moment of truly flat wavefronts, but adding all the distortions up taking the average should result in something approaching flat. Put differently, it does not make sense to alter the optical design to correct for e.g. concave spherical wavefronts due to seeing, because the perturbations are random

Another way to look at it, is that the perfect wavefront is perfectly flat, Likewise, the average wavefront in poor seeing is flat, so optics that correct superbly for a flat wavefront are best on average. It is possible, but extremely unlikely that a wavefront distorted by seeing happens to correct for any imperfection in the optics, but a little maths will show the chance of this is vanishingly small, or at least far smaller than the chances of having fleeting moments of near flat wavefronts in situations of poor seeing.

In my first solar imaging session since August 25, 2022 (!), I finally got good weather, and time to set up the solar kit. I set up the APM 80mm F/6 triplet on the Vixen Great Polaris mount, with the Beloptik Tri-Band ERF. For white light I used my Lunt Herschel wedge, ASI178MM camera, and Baader Solar Spectrum filter. An extra UV/IR block wasn't needed due to the Beloptik ERF. Not much could be seen in white light. Sun WL, grey scale: Sun WL, pseudo-colour: In Ca-K a lot more activity could be spotted. Here I used my Lunt B1800s Ca-K module, with the ASI178MM. Again 500 frames stacked out of 2000. Sun Ca-K: grey scale: Sun Ca-K, pseudo-colour: Sun Ca-K, part inverted: Sun Ca-K, part inverted, pseudo-colour: The most detail was visible in H-alpha, as ever. This was taken with the Solar Spectrum 0.3 Å H-alpha filter, Baader TZ-4 4x tele-centric lens, and ASI174MM camera. Given the larger focal length, I needed a 15-pane mosaic to cover the entire disc. Each pane is a stack of 300 out of 1000 frames. Sun H-alpha, grey scale: Sun H-alpha, pseudo-colour: Sun H-alpha, part inverted: Sun H-alpha, part inverted + pseudo-colour: Clicking to see the full-resolution versions is highly recommended, especially in the case of H-alpha

Superb collection. Solid cloud here, alas

Impressive stuff and very instructive. It is indeed staggering how much easier it is to see, e.g., the Horse-Head Nebula than to spot it, even from a dark site as a seasoned observer. Besides, even with something as bright as the sun, certain things are next to impossible at the eyepiece, like this stuff: Ca-K is essentially invisible to me with my glasses on, and something very deep purple with little or no detail without glasses (too old for 393 nm, I suppose)

Managed to catch some rays during lunchtime, setting up the Coronado SolarMax-II 60mm. The first thing that struck me was the range of spots, filaments and plage areas on the disk, along with some prominences sticking out from the limb. One particularly long one could be seen at the 9 o'clock position, with a smaller one at 6 o'clock. The large AR with two huge sunspots on either side, some distance below the centre of the disk also showed two curved filaments that almost touched each other. At 13:20 local time (11.20 UTC) I suddenly spotted a bright, linear structure that almost seemed to link the two filaments together, almost like a spark arcing across the gap between them. It subsided after about 10 minutes, and spaceweather confirms there was a minor flare (C1.01) at that time. Really nice to have spotted it

That sounds like it was a flare

I have a 14mm Delos, and I remember it took a bit of getting used to. In particular, I tried a couple of different positions for eye-cup, and once I found the optimal, I locked the top of the upper barre in that position and haven't changed it since. I did the same for the 8mm Delos I bought later. I still find it a smidgen less comfortable than the Pentax XWs, but still very nice to use. The ES 12 mm 92 deg monster I have is an absolute gem, but I also needed to find the right eye position in that one (and the 17 mm as well).

Nice work. Cloudy here (again) alas

Welcome to SGL. I am located in Groningen in the north of the Netherlands, and my garden is Bortle 4-5, so quite a bit better. If you are ever in the neighbourhood, feel free to drop me a line. There are some good dark sites in the area.

It's been pretty dismal here too

Got the Coronado SolarMax-II 60 mm out for a spin during my lunch break. A huge prominence between the 10 and 11 o'clock positions immediately jumped out at me. It looked like a huge candle flame, probably some 120,000 km high. It is in the same area as the big prom I spotted two days ago, but it has clearly changed shape (if it is the same). Just below the 9 o'clock position, a detached prom, showing up as a red blob at about half the height of the big prom from the sun's limb. There are many minor proms around the eastern limb, in particular near the big sunspot close to the limb at the 3 o'clock position. About halfway between the disc centre and the limb, in the 10 o'clock position, two very compact, very dark filaments are visible. Detuning did not show much in the way of sunspots at this location, so despite their dark appearance on-band, they are not sunspots. above them some weak plage can be spotted. Lower on the disc, towards the 7 and 8 o'clock position, various areas of brighter plage can be spotted. Several students and faculty members dropped by to have a look, and they were all suitably impressed with the show the sun was putting on.

Well deserved! Congratulations

Just had another look, and it is still going strong

Just took the Coronado SolarMax-II 60mm for a spin during my morning tea break, and there is a huge prominence high up on the northern limb of the sun. It looks like two huge, near linear flames emanating from the disk, the right-hand one a lot bigger than the left-hand. There is quite bit of other activity in the form of smaller proms along the western limb, a couple of sunspots, and a scattering of plage areas and filaments on the disk. Well worth a look. Pity I do not have imaging gear at work

Magnificent stuff!

I have a Meade Schmidt-Newtonian, and just attach the camera (ASI183MM) and filter wheel into the focuser, and achieve focus quite easily. I would assume the same works on the Mak-Newt