ROAST :: 2026

Update, June 13/14
Another go last night, and here’s a mega stack of the two sessions:

Some more detail, and the surrounding nebulosity has been brought out a bit more. I tried raising the gain to 70 and reducing exposure time to 15 seconds, mainly to see what diference it made; the increased noise is probably due to the extra gain, so I won’t be trying that again. There were 36 failed shots this time, some satellites but mostly because it was very windy resulting in smeared stars.

Details:
Target: C34, Witch’s Broom nebula
Time:
A: 2026-06-11 00:17..01:23
B: 2026-06-14 00:11..01:39
Equipment: Dwarf Mini, Duo-Band filter
Integration:
A: 49mins (98×30secs, +7 failures), gain 60
B: 66mins (264×15 secs, +36 failures), gain 70
Total: 1hr 55mins
Conditions: Clear but windy, Bortle 7
Processing: PhotoDesk equalisation, gamma (blue and rgb), balance

Original post
June 10/11, another few hours of clear skies. After doing the wide mosaic of the Veil Nebulae recently, we were intrigued by the colours in the Witch’s Broom part. They weren’t very prominent so here’s another go, this time concentrating on the Broom, Caldwell 34.

The Dwarf Mini has two main filters available: Astro, which enhances infrared and is mainly used for galaxies and solar system objects, and Duo-Band, which is designed to emphasise the Hα and O III parts of the spectrum — that is, ionised hydrogen at 656.3nm and oxygen at 500.7nm. These emissions are prominent in nebulae and are shown as reddish and bluish colours respectively. This filter also reduces glow from moonlight and general light pollution (street lighting and so forth), so is pretty useful.

I didn’t have time for many exposures, so this is intended as the first tranche of a mega-stack. It’s a fairly faint object and needs hundreds of shots — perhaps 3 or 4 hours of integration — to really bring it out. I’m also not too happy with the processing, but it’s a start.

Details:
Target: C34, Witch’s Broom nebula
Time: 2026-06-11 00:17..01:23
Equipment: Dwarf Mini, Duo-Band filter
Integration: 49mins (98×30secs, +7 failures), gain 60
Conditions: Clear, Bortle 7
Processing: PhotoDesk equalisation, gamma (blue and rgb), balance

And so to bed…

June 8/9, and at last a couple of hours of clear sky. We’re approaching the solstice now, and observing is limited to between 11pm and 3am or so.

I started with a perfect EQ alignment just before 11pm, and aimed the scope at the star Sadr, the central star in Cygnus, when it finally moved out from behind a tree. On the right is the view to the east at about 11:00 pm; Sadr is the star under the “g” of “Cygnus”, and it’s in the centre of a large area of nebulosity known as the Gamma Cygni Nebula, the Sadr Region, or IC 1318.

Below is the result of the session. Sadr itself is the fairly bright (magnitude 2.2) star in the centre of the image.

The small group of stars at top centre is the Inchworm Cluster, NGC 6910.

The long dark lane at lower left is the “body” of the Butterfly Nebula (the Cygnus one — there are a number of similarly named features elsewhere in the sky). The large “wings” are at centre left and (off-screen mostly) bottom left. This area is so large it really needs a mosaic!

It’s interesting to compare my effort with this image, taken with much more expensive equipment.

Details:
Target: Sadr, HD 194093
Time: 2026-06-08 22:50..00:18
Equipment: Dwarf Mini, Duo-Band filter
Integration: 1hr 15mins (150×30secs, 1 failure), gain 60
Conditions: Clear, Bortle 7
Processing: PhotoDesk equalisation, gamma

Just after midnight the Elephant’s Trunk nebula also became visible (that damned tree!); it’s halfway between Cygnus and Cepheus but is technically in Cepheus. I aimed the scope slightly off to get a bit more of the surrounding nebulosity in the picture.

The “Trunk”, or IC 1396A, or Sh2-131 — there are a hell of a lot of these sky catalogues, aren’t there? — is the curly bit at lower right. It’s embedded in the large nebula known as IC 1396, and is being illuminated by the brightest star at centre bottom, HD 206267.

Details:
Target: Elephant’s Trunk Nebula, IC 1396A
Time: 2026-06-09 00:23..01:32
Equipment: Dwarf Mini, Duo-Band filter
Integration: 1hr (120×30secs, 5 failures), gain 60
Conditions: Clear, Bortle 7
Processing: PhotoDesk equalisation, gamma

This is a bit noisy, and would benefit from more exposures. I’ll try it again (skies permitting) and stack them all together.

And so to bed…

May 25/26, and another lovely clear night. This time I didn’t stay up, but programmed a session with two targets: M57 again, the Ring Nebula in Lyra from 11pm to 1am, and a mosaic of the Veil Nebulas C33 and C34, which are parts of a large complex called the Cygnus Loop; 1am to 3:30am. This is the remnant of a supernova that exploded about 8,000 years ago. The parts shown here are the Eastern Veil on the left, aka NGC 6992, and the Western Veil on the right, aka the Witch’s Broom; collectively aka Filamentary Nebulae. The fainter bit at top right centre is Pickering’s Triangle. Click for enlarged view.

Details:
Target: C33,C34; 4-frame mosaic
Equipment: Dwarf Mini, Duo-Band filter
Integration: 39mins/frame (77×30secs, 3 failures; total 228 frames), gain 60
Conditions: Clear, Bortle 7
Processing: PhotoDesk equalisation, gamma

This ideally needs longer than 40 minutes per frame to get a better result, but it’s difficult at this time of year, with short nights.

Here’s a megastack of the Ring Nebula, combining the shots taken last night with those from 25 April:

Details:
Target: M57 megastack
Equipment: Dwarf Mini, Duo-Band filter
Integration: 2hrs 30mins (300×30secs, 3 failures), gain 60
Conditions: Clear, Bortle 7
Processing: PhotoDesk equalisation, gamma, x2 scaling

And finally, the Moon:

May 24/25, and the first clear night for over three weeks — with a few more to come, hopefully.

The summer is approaching, and with it comes the Summer Triangle of Deneb, Vega and Altair, the three brightest stars in Cygnus, Lyra and Aquila respectively. Cygnus is especially interesting due to the number of nebulae in the area and a fairly bright section of the Milky Way. So here’s Caldwell 27, aka NGC 6888, aka the Crescent Nebula:

This emission nebula is just below Sadr, the central star of Cygnus. The star in the centre is WR 136, which about 120,000-240,000 years ago became a red supergiant and threw off the material that became the nebula. It’s expected to explode in a supernova at some point.

The area around Cygnus is rich in nebulosity, some of which can be seen here.

Details:
Target: C27
Equipment: Dwarf Mini, Duo-Band filter
Integration: 1hr 9mins (69×60secs, 1 failure), gain 60
Conditions: Clear, Bortle 7
Processing: PhotoDesk equalisation, gamma

I also tried out the new Milky Way setting on the Mini, with rather poor results. It seems you need properly dark skies for this to work well. And I clearly didn’t give it long enough.

Details:
Target: Milky Way, Cygnus area
Equipment: Dwarf Mini
Integration: 33mins (201×10secs, no failures), gain 40
Conditions: Clear, Bortle 7
Processing: PhotoDesk equalisation, gamma

The smear on the left is a tree, and there’s obvious light pollution on the right.

Now I’ve had the Dwarf Mini for a while I’ve developed a few methods to process the images using PhotoDesk, and here I’ll run through one possible approach. Processing astronomical images is always a balance between accuracy and aesthetics, but the most important thing is to preserve as much data as possible without adding too much (ideally, anything!).

The Mini produces a number of files for each observing session. Most importantly you have access to the raw data, with each shot — often hundreds of them — saved by default in FITS format (you can get them as TIFFs if you so choose). These contain 16-bit data which is unaligned, and undemosaiced¹. They’re currently not really usable under RISC OS, unfortunately, though hopefully that will change² .

But you also get aligned, demosaiced and stacked versions of the data in the form of high-quality PNG and FITS files — and, for our purposes, as a JPEG. It’s not ideal working with JPEGs, but it’s what I’m stuck with at the moment. And you can get pretty good results with some careful processing.

[Read more…]

The last clear night for a while according to the forecast, so I decided to attempt scheduled shooting for the first time, and try out a mosaic. The Mini lets you program an observing session in advance, with one or more objects, and each can use the mosaic feature which stitches together up to four fields of view into a single image.

The target was C20, aka the North American nebula in Cygnus; it’s obvious why this very large area of nebulosity is so named. This is really a summer object at my location, but as we’re now in May it becomes visible after 2am or so. I wasn’t going to stay up that late, so programmed a schedule to start at 2:00am and continue shooting until 4:30am, when it would start to become lighter. At 11pm I put the scope on a tripod outside with a battery plugged in, set up a perfect equatorial mount, and synchronised the schedule. Then I went to bed. A bit nervously!

So at 2:00am the scope woke itself up, and took 225×30 second exposures at gain 60 with the Duo-Band filter. And here’s the result:

Click for (much!) bigger. It’s been lightly processed in PhotoDesk (gamma adjustment), and the Mini has added ’spikes’ to the brighter stars (a new feature in the latest upgrade) to simulate a more usual astro photo. Star spikes are caused by diffraction around the mountings for the secondary mirror in many telescopes — including the Hubble, incidentally.

The stitching together isn’t quite perfect; there’s a visible discontinuity in the lower right quadrant. Better processing would mitigate this.

I actually started the session at about 10pm, and to check that everything was working properly I imaged M106 again. Here’s a Mega Stack of last night’s result with the images I took on 6 April:

It’s been lightly gamma processed in PhotoDesk and cropped to remove some satellite trails — the Mini’s removal of these shots isn’t 100% accurate.

Another clear night, another perfect equatorial alignment, and another hard target — this time because it’s so small:

Click for bigger. This is M57, the Ring Nebula in Lyra, a constellation becoming more visible as summer approaches. It’s a planetary nebula, formed when a star heading towards the end of its life throws off some of its atmosphere prior to becoming a white dwarf. The image has been lightly processed in PhotoDesk, and has been x2 enlarged. 110 shots with two failures (satellites), 30-second exposures, gain 60 and Duo-Band filter.

And to take advantage of the clear sky, here’s another go at Bode’s Galaxy:

145 shots with one failure (satellite), 60-second exposures, gain 60 and Astro filter.

A crystal-clear night, and having set up a perfect equatorial alignment - it only took a single adjustment; I’m getting better at this - I decided to try for longer exposures on a few targets.

First I targeted NGC 4216, or the Silver Streak galaxy, an edge-on spiral in the Virgo cluster of galaxies. I took 71 shots, of which 5 were failures (Starlink satellites again). Exposures were 60 seconds, with gain 60 and the Astro filter. It’s been post-processed lightly in PhotoDesk, with a small equalisation and gamma adjustment.

Click for much-enlarged view; the target galaxy is in the centre. Various other galaxies are visible here, including NGC 4267 at lower left, NGC 4222 and NGC 4206 above left and below right of the target, and NGCs 4189, 4193 and 4168 on the right. Plus others.

Using long exposures (over a minute) really needs an excellent alignment, so I tried 2-minute exposures on a really hard target: Coddington’s Nebula in Ursa Major. Misnamed, as it’s actually a galaxy thought to contain a lot of dark matter. This is 37 shots with no failures - too late for Starlinks, hah - with 120-second exposures, gain 80 and the Duo-Band filter. The ‘nebula’ is actually pretty faint and barely shows on the original image, but some quite aggressive post-processing in PhotoDesk (gamma, equalisation and balance) has brought it out.

[Updated 14 April 2026]
Another clear night, and another go at C/2025 R3 (PanSTARRS). Started earlier this time, and managed more shots and a slightly higher gain:

This was 60 15-second photos at gain 70. Gamma and equalisation in PhotoDesk. I centred the shoot on a star slightly above the comet, to get more of the tail in.

Comets are fairly fast-moving things, especially when near the sun, and a current limitation of the Dwarf Mini is that it tracks the stars, not the comet. You can see there’s a slight elongation of the comet’s head here, as it’s moved slightly over the course of the exposures.

Here’s a screenshot of the in-progress shoot, showing the location between the trees:

[Original post:]

Comets are tricky things to image. They’re brightest when they’re closest to the sun, which means they’re low in the sky and best visible around sunset or sunrise.

There’s a comet around now with the rather unexciting name of C/2025 R3 (PanSTARRS). There’s a naming convention here: the “C” denotes a non-periodic comet (meaning it’s unlikely to return); “2025 R3” gives the year and half-month when it was first observed (so “R”, the 18th letter, is the first half of September, the 9th month) and it’s the third comet discovered in that period; and “(PanSTARRS)” is who or what discovered it, in this case the automated sky survey system Pan-STARRS in Hawaii.

As of today, 13 April 2026, it’s low in the eastern sky before sunrise. We’re surrounded by houses and trees here, but looking at the comet in Stellarium it looked like it might be observable from an upstairs window between a fortuitous gap in the trees, at around 5am.

And indeed it was!

This was 25 15-second shots at gain 60, with two failures: one satellite, and one tracking problem, unsurprising given the comet’s altitude (about 10°) and proximity of dawn. It would have been better to take a lot more shots with longer exposures, but the sky was inexorably lightening as the dawn approached.

The alarm was set for 4am, and while waiting for the comet to rise I tested out the Mini by imaging the North American nebula, as below (or part of it — the bit here is Florida and the Gulf of Trump America Mexico; rotate it 90° clockwise and you can see the vague resemblance). It was fortunate I did this, as the focus was clearly off somewhat. Still, a preview of what will be available in the summer months at more sensible times.

A few nights ago I took some more images of Markarian’s Chain, and while it wasn’t a great session (clouds), I did learn something about when to observe.

I took 210 photos with 30-second exposures, and the Mini rejected 14 of them — all due to satellites, mostly Starlinks I think.

Here’s a quick manual stack of the rejected frames:

They haven’t been demosaiced or aligned (hence the green tint); I just wanted to see the satellite tracks, all in a pretty small area of the sky.

What I learned was this: sessions should start as late as possible. I started imaging at 9:10pm, and finished at 23:12. All the failures happened before 22:22pm, by which time the sun had moved far enough below the horizon that the satellites weren’t illuminated any more — all those Starlinks are in low orbit.

Unfortunately, that means that in the summer (shorter nights) we’ll get many more trails. :-(