Sun, Moon and Ruins: a partial eclipse

The enigmatic venue behind this post: Reculver Towers and Roman Fort on the north Kent coast (UK), photographed in the early morning. This beautiful site is managed by English Heritage; the image above is taken from their website – here.

The enigmatic venue behind this post: Reculver Towers and Roman Fort on the north Kent coast (UK), photographed in the early morning. This beautiful site is managed by English Heritage; the image above is taken from their website – here.

Partial eclipses of the Sun by the Moon are not particularly rare. There have, for instance, been five of them visible from the UK in the decade leading up to the most recent, when ~90% of the Sun was occluded by the Moon shortly before sunset on 12th August 2026. Total eclipses, by contrast, are harder to come by unless you’re willing to travel; the last one visible from my spot on the globe was in 1999 – and it was obscured by cloud. C’est la vie.

Most people are aware of the cause of an eclipse: the Moon covers the Sun for a short period of time when viewed from the right place on the Earth’s surface. If they line up perfectly from our perspective then we’ll witness a total eclipse[1], a little bit off-centre and we’ll be able to enjoy a partial eclipse of one degree or another. This relies on two facts: although the Moon is 400 times smaller than the Sun it is also, on average, 400 times closer to us[2]; also, the Moon orbits the Earth in pretty much the same plane as the Earth orbits the Sun. Thus, the sizes are just right and the chances of everything lining up are good. If you’d like a basic animated explanation, try this cartoon from Nasa, and if you want to know why we don’t see one every month, try this one-minute explanation.

 

Hopefully, these images will illustrate the importance of size. At the top are images from NASA: the August 12th total eclipse as witnessed in Spain and the not-so-total eclipse generated by the largest of the two small Martian moons, Phobos. The latter was taken from the surface of Mars by a camera on the Perseverance rover. See here for details on the Phobos image; for the Moon images see here and here. (For the image of the Martian moon Phobos passing in front of the Sun I am grateful to Andrew and Ben, fellow members of my amateur astronomy society, for reminding me of its existence.) My own image of Callisto crossing the face of its parent planet – look for the dot on Jupiter’s face at the 1 o’clock position – prompts a further illustration of the effect: all four of its larger moons, the Galilean moons – Io, Europa, Ganymede and Callisto – are able to generate a total solar eclipse if viewed from the top of Jupiter’s clouds. This is for the simple reason that the Sun appears tiny at that distance: Jupiter is five times as far away from the Sun as we are on Earth and the Sun therefore appears to be only a fifth of the size. Thus, even the smallest of Jupiter’s Galilean moons, Europa – which is only about 90% the size of our Moon – is easily able to cover the Sun.

That’s probably enough by way of introduction and background, but if you’d like to read more about the Sun then please explore my blog (e.g. here). The intended focus of this post is the deep partial solar eclipse on August 12th when, from my part of the world, the silhouette of the Moon covered approximately 91% of the Sun’s face at its peak. The peak occurred at 19:13 local time and from start to finish the Moon’s transit across the Sun lasted about 110 minutes. The end of the event occurred shortly before sunset (20:10), by which time the apparent circular shape of the Sun’s disk had been distorted by the atmosphere into an oval. Given the timing, it was important to observe the event from a location with an unincumbered horizon. Thankfully, I’m surrounded by nearby coastline having a view across the North Sea towards the setting Sun.

The excellent amateur astronomy society I’m a member of, SEKAS, does a lot of community outreach, which I enjoy, including joint events with English Heritage. On this occasion, the joint venture was to be held at their medieval church and Roman fort site at Reculver on the north Kent coast (southeast England). The site occupies raised ground right on the coast and provided the perfect venue since we could view the Sun through to its setting into the sea’s far horizon. Thus, five SEKAS amateur astronomers had between them ten telescope-based setups of various kinds to allow a safe view of the Sun whilst the English Heritage people made available free solar viewing glasses for those people who’d pre-registered online. (There was a shortage of the ISO 12312-2 safety standard viewers in the days leading up to the event and prices rose to ridiculous levels. My own stock, purchased months beforehand, went as gifts to family, friends and English Heritage. Thankfully, the lovely people from my local Beacon Astronomy Group arrived with a box full, which they handed out as needed. I also saw many people sharing what they had with those around them, which was good to see.)

For my part, I took two telescopes [3] as well as a semi-automatic astronomical camera for recording images. I’d also made a pinhole camera from a shoebox … just for fun. For a ‘normal’ outreach event this would have been more than enough. However, apart from English Heritage’s own publicity, BBC local news had listed the event as one of the best ways to observe the partial eclipse. Thus, despite turning up three hours before the event began in order to be able to park and to set up, individuals and family groups arrived soon after wanting to ask questions and to look through the telescopes. In the end, an estimated 1,000 people were spread over the grassy banks around the site and we were constantly busy for almost five hours. It was exhausting, but also huge fun and very rewarding. I spent the whole time skipping between my three telescopes, answering questions and being shown images that people had captured through a telescope eyepiece or with their solar viewing glasses held over their smartphone camera lens. Thankfully, I had my daughter and a grandson there to lend a hand when needed, and my wife rescued me long enough to allow me to eat a sandwich, take a long drink and generally cool down in the shadow of the two towers.

A selection of monochrome stills extracted from my ‘roboscope’. From left to right: the Sun just before the eclipse began with the visible sunspots labelled; a few minutes into the eclipse as the Moon begins to occlude the solar disk; moments before the peak of the eclipse – I missed the actual peak as I was busy helping someone see it through a telescope and I also missed the fact that the ‘roboscope’ exposure length had changed such that everything was over-exposed; the final stage of the eclipse as the Moon’s silhouette moves off to the left. You’ll notice that in the rightmost image the atmospheric distortion has given us an oval disk with surface details like the sunspots blurred due to turbulence. I converted the original images, each of which was derived from a stack of 40 individual frames processed in AffinityPhoto2, from colour to monochrome because the solar filter on my ‘roboscope’ has the annoying property of making the Sun look orange-yellow rather than its natural off-white.

A selection of monochrome stills extracted from my ‘roboscope’. From left to right: the Sun just before the eclipse began with the visible sunspots labelled; a few minutes into the eclipse as the Moon begins to occlude the solar disk; moments before the peak of the eclipse – I missed the actual peak as I was busy helping someone see it through a telescope and I also missed the fact that the ‘roboscope’ exposure length had changed such that everything was over-exposed; the final stage of the eclipse as the Moon’s silhouette moves off to the left. You’ll notice that in the rightmost image the atmospheric distortion has given us an oval disk with surface details like the sunspots blurred due to turbulence. I converted the original images, each of which was derived from a stack of 40 individual frames processed in AffinityPhoto2, from colour to monochrome because the solar filter on my ‘roboscope’ has the annoying property of making the Sun look orange-yellow rather than its natural off-white.

The animated sequence of all the individual images I captured that afternoon is above; it may also be accessed on my YouTube channel, using the link here. Ben Harding, chair of SEKAS and the co-organiser of the event with English Heritage, was interviewed by ITV news – see here and scroll down to the Reculver section. Another video, which is well worth viewing, was recorded by a local multimedia journalist, Q Cummins, Kent reporter for Herne Bay based Hits Radio and Greatest Hits Radio. It captures the response at the peak of the eclipse from the good-natured crowd of people watching the event. This short video is shared with the kind permission of Q Cummins / Bauer Media, to whom I am grateful:

Best of all were the lovely, inquisitive people – from toddlers to pensioners, both locals and those here from countries in mainland Europe and as far afield as the USA and Japan – who came, talked and observed, and who made the outreach event one of the highlights of my amateur efforts. The following images were taken by my wife or daughter or SEKAS members …

Footnotes:
[1] There is a caveat to this in that the Moon’s orbit is not perfectly circular and so the Earth–Moon distance does vary slightly; if it passes in front of Sun when at its furthest from Earth – when it therefore appears to be a little smaller – we see an annular eclipse. This gives us a narrow ring of sunlight circling the Moon’s silhouette rather than a total eclipse. A full Moon is often given the name ‘Super Moon’ if it coincides with the point in its orbit when it’s closest to the Earth. Either way, the Moon covers only about ½° of the sky – as does the Sun – and can be hidden behind one of your fingernails when held at arm’s length.

[2] Eclipses haven’t always been exactly as we witness them today. Way back in the Cambrian period (~500 million years ago), when the first explosion of life was taking place, the Moon was much closer to the Earth. The Moon would therefore have appeared significantly larger in the sky and would have hidden the Sun more easily. In addition, the Earth was spinning faster: a day lasted only about 21 hours and each year comprised a little over 400 days. The Moon is still moving away from us (at approximately 38 mm/year) and our days are still getting longer (by a couple of milliseconds each century).

[3] For those who like detail: a 150/1200 mm Newtonian with a 32 mm eyepiece on a manually operated equatorial mount; a 72/420 refractor with a 25 mm eyepiece on a Sun-tracking mount; a ‘robotic’ imaging system which tracked the Sun and displayed captured images in real time on my smartphone. The imaging system (a Dwarf3) had proprietary solar filters fitted. The two telescopes were fitted with bespoke homemade filters - see here for details.)

Although the perceived brightness of the day doesn’t change noticeably through a partial eclipse because our eye-brain combo compensates, even during a partial eclipse as deep as this one, the temperature did fall noticeably. My objective evidence for this came from the ‘roboscope’: its internal running temperature was 59°C during the early stages of the eclipse, but by the peak this has dropped by 10°.

Too much Sun?

What a day: the last of the second heatwave in the UK year (so far) with temperature records having been broken multiple times and the whole thing made far worse by elevated levels of humidity; and what did I choose to do? I chose to stand in the Sun from ten in the morning until gone three in the afternoon.

Crazy? Maybe – but I prefer to believe that it was because I had the welcome chance, with three friends from my local amateur astronomy society, SEKAS, to show people our life-giving local star in all its energetically chaotic glory. The event that gave us this opportunity was my local village fête which, despite the uncomfortable weather, attracted large numbers of individuals, couples and families. Some of these lovely people I knew already, others I was meeting for the first time – either way, there were so many of them interested in what we were doing that the four of us barely stopped talking throughout the day. (The exception to this were the necessary times when we tried to keep hydrated; I was glad of the many bottles of chilled water I’d packed into a ‘cool-bag’ … and my sunscreen and wide-brimmed hat.)

Back in April I had contacted the Village Hall Committee, who support the annual fête’s organisation. Via our local social media page, I floated the idea of offering a safe solar observing experience. I’d half expected that I’d be told that it wasn’t really the sort of thing for a community fair – but the organisers evidently have a wider vision 😊. As a lovely bonus, the person who replied to my email, Tricia, reminded me that she’d stopped to chat one night whilst walking her dog – I was in my front garden with a telescope, naturally – and that I’d offered some advice on buying a telescope. Apparently, she now owns one … excellent!

In the two months between the gift of a south-facing pitch and the fête actually happening I had offers of help and support from fellow members of the South East Kent Astronomy Society – phew! I also tried to prepare the ground a little by posting a few of my own solar images so that people might get an idea of what to expect: “Just to whet your appetites in advance of the Blean Village Fête – at which, clouds permitting, you'll be able to see this sort of thing for yourselves - here's a some images of the Sun taken a few days ago from my garden. We'll have special equipment with us to enable you to do this safely - please, please, please don't look at the Sun directly as you can easily cause damage to your eyes ... and never, ever through binoculars or a telescope as blindness will follow. The whole-disk image was taken using a filter which let's all colours of the rainbow through but reduces the total by 99.999% in order not to damage the camera. Notice the three active regions (aka sunspot groups). Next is a close-up view around one of the sunspots - but this time it's taken using a specialised filter which only permits through one particular wavelength (colour) of light which comes from energised hydrogen. This has the beauty of picking out the chaotic and very energetic surface magnetic field associated with sunspots - just look at those swirls! Do you notice that there are whiter patches to complement the cooler dark sunspots? These are called plages, and they are regions where the surface is hotter than average. The darker loops are prominences that we're effectively observing from overhead. Finally, by over-exposing the disk of the Sun I managed to capture a very impressive prominence: super-hot plasma thrown out into space along the Sun's magnetic field lines. This one is many, many times the size of the Earth.”

Arriving at 10 am, we spent the next hour setting up an array of telescopes and getting their associated bits and pieces powered up. There were three fully automated ‘roboscopes’ in use as part of this array and they attracted a lot of attention. Mostly, this went smoothly – apart from one of my accessories which simply wouldn’t play ball; there’s always one. (Photos by the SEKAS Chairman, Ben Harding, and by the person who has responsibility for the SEKAS observatory site, Ashley Fuggle.)

We tried to introduce the experience by using a simple Newtonian reflecting telescope with its image projected onto a white background. Not only does this serve to illustrate that the Sun’s native colour is off-white and not yellow, but it revealed the sunspots nicely. (I’ve written about the colours of the Sun before if you’d like more background information: here and here.) Also, by placing a piece of card at the focal point of the telescope and noticing that it starts burning very quickly one immediately sees why looking at the Sun without appropriate equipment is a seriously bad idea. Other telescopes revealed crisp images of our white Sun and the day’s active sunspot regions by filtering out the majority of its light before it even enters the telescope itself. These are called white-light filters because they allow through a tiny fraction of all the colours (wavelengths) of the rainbow.

This is a colour image of the Sun taken on the day (by Ashley Fuggle, cropped and augmented by me) using one of the three smart telescopes in use – these impressive ‘roboscopes’, which may be controlled from an app on a smartphone, have a built-in astronomical camera. Each active region (- in this case a sunspot or group of sunspots) is given a numerical designation; for example, the large group centre left is AR-4478. To give you a sense of scale, the blue dot to the left of that region represents the size of the Earth: one could fit 109 ‘earths’ across the diameter of the Sun’s disk.

A highlight of the day for many people was the chance to look at the Sun not in white light but through a filter which eliminated all the wavelengths (colours) of light other than one of the wavelengths emitted by hydrogen, which happens to be a pinkish red. The advantage of this special and highly non-trivial method is that one can observe the flame-like prominences shooting out from the edge of the Sun’s disk. Prominences, the shape of which is influenced by the Sun’s strong magnetic field, are made from the Sun’s matter; in the main, this material falls back into the Sun under the action of its gravitational attraction. Sometimes however, the material has enough energy to break free and to stream out into space as a solar flare – if one of these travels in our direction then, a couple of days later it’ll arrive at our atmosphere and generate the aurora (the Northern and Southern Lights). If it’s powerful enough, we can even see the Northern Lights in the south of England. (Images by Ben Harding, edited by me.)

All-in-all a lovely, if hot, day for those of us who’d volunteered to offer the experience – and judging by the comments made on the day and on the village’s social media page in the days after, the whole thing was a great success. We’d love to return next year if they’ll have us. In fairness, I ought to share the comment of one person who declared that they’d already seen too much of the Sun and didn’t want to see any more – oh well, it’s not possible to please all of the people all of the time 😉

The House of Astronomy: Astrofest

It was my first time.

I’d toyed with the idea before, more than once. Attending a genuinely large-scale amateur astronomy event had been an appealing thought ever since I had reacquainted myself in retirement with the chief of my geeky teenage hobbies, but … The annual European Astrofest, held this year in Kensington Town Hall, London, was too good a chance to miss. Apart from anything else, we’ve had two years of the most miserably damp and cloudy Winters in my part of the world with telescopes tucked away unused – so, in the absence of ‘traditional’ cold, crisp and clear nights, maybe a conference on astronomy would cheer us up.

I travelled with three fellow members of the South East Kent Astronomy Society (SEKAS). It was a long day – beginning with an alarm at 05:00 so that I could catch an early train to London, meet my SEKAS friends and be at the venue in good time for the first of several talks. SEKAS is one of three local amateur astronomy groups that I count myself a member of, but it holds two key advantages for me: it is dedicated to outreach and that resonates with my own longstanding passion for science communication, and it streams its monthly meetings online. The latter is really useful to those of us who choose not to drive on less familiar roads after dark. (It’s sad that the three SEKAS outreach events I participated in recently were all messed up by cloud and rain.) One of the very first happy discoveries of the day was that the SEKAS crowd have a tradition of buying a breakfast in a small, but perfectly formed, café off Kensington High Street. I’m glad I’d only had a very light pre-dawn breakfast, but this still made me feel a little like a hobbit enjoying Second Breakfast. I’m grateful to Andrew for supplying photographic evidence.

Astrofest ran for two days, but I booked in for the second day only. In future years I’d be tempted to do both days given the quality of the talks and the breadth of the trade/society exhibits spread over three floors. There were two talks on the Friday schedule for this year, for instance, that I’m particularly sad about missing: Prof. Michele Dougherty, the Astronomer Royal and a principal Investigator on missions to Saturn and Jupiter, and Sir Brian May who recently published a book of 3D galactic images. However, I enjoyed several excellent talks on the day I was there which covered a range of contemporary research as well as a wonderfully nostalgic look at what is still, after more than four decades, my favourite space exploration mission.

A quick snap on my phone before the lights went down and one of the talks got started – just to illustrate the fact that these sessions had audiences of several hundred amateurs like me.

First up was Dr Steph Yardley and her stunning images and video clips of the Sun derived from ESA/NASA’s Solar Orbiter data. In complete contrast, Josh Howgego talked about his own home-grown attempts to sift out from the detritus in his gutters a few examples of the enormous quantity of micrometeorites that reach the Earth’s surface each day. There’s no doubt that his science journalist’s take on the subject will motivate the clearing of a great many gutters in the next year or two. Moreover, it reminded me of a recent research project supervised by a space scientist at my own former university (Dr Penny Wozniakiewicz) which involved vacuuming the roof of Canterbury Cathedral. There were talks which reviewed ESA’s past, present and planned solar system missions; that looked at the use of polarised light as a means of mapping a galaxy’s magnetic fields; that considered the engineering challenges associated with making the very best telescope mirrors; which outlined the NASA Psyche mission en route to an asteroid primarily made of iron and nickel. However, the session that dug deep into my lifelong fascination with space exploration was the interview of Dr Garry Hunt by Prof. Lucie Green. Garry had been the only British Principal Investigator on the imaging team associated with the Voyager missions. Almost irrespective of what he actually said – which was interesting in its own right – it was such a pleasure to be able to revisit this pair of amazing ‘grand tour’ missions. It’s also salutary to remember that after decades flying at truly prodigious speeds the Voyager satellites are still less than one light-day away. (The nearest stars are, remember, several light-years away.) As Douglas Adams informed us in his radio play The Hitchhiker’s Guide to the Galaxy* “Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is”

A very low-quality image of Garry and Lucie on stage discussing the Voyager missions. In passing, the monitor screen to the right displayed speech-to-text in real time: it was surprisingly effective, even for one later speaker who had a heavy accent.

Much as I love learning, there was more to the day than that alone. For example, it gave me another opportunity to spend time with and to get to know better some of my fellow SEKAS members and astro-enthusiasts. Not only do they possess between them a seemingly inexhaustible fund of useful and constructive advice, but they’re also a pleasure to be around; it’s a nice combo. Beyond that I had the fun of putting faces to the names I’ve been coming across online for a while: the folk from First Light Optics for instance, from whom I’ve bought an embarrassing number of bits and pieces#, and individuals like Gary Palmer who got me started on imaging the Sun using narrow-band filters (see my earlier post here). Mary McIntyre, who is a frequent contributor to the BBC Sky at Night magazine, was running a workshop on lunar sketching; I wish I could, but it would be embarrassing. The national astronomy societies and several interest groups were there in force, some of which I’ve been supporting for years: the BAA for instance, and Dark Skies (see also here).

One DIY display caught my eye. It was the SKAO (- originally the Square Kilometre Array, SKA, back in the days when I first started hearing about it). Hardly a DIY project on the face of it, but they showed a demonstration of a basic radio telescope fabricated from an umbrella, a tin can and some simple circuitry connected to a laptop. With it, they claimed to be able to detect the arc of the Milky Way. I might have a go at this one day – at the very least it would give me something to do on a cloudy day.

And then there is the abundance of opportunities to spend money … I mean, serious money! I resisted, naturally 😉. However, that’s not to say I didn’t gaze with a modest level of avarice now and again. For instance, there was a display outlining the plan for an observatory hosting site in Oman away from serious light pollution and in a location boasting ten times as many clear nights per annum as I get. There are several such sites in existence around the world already of course – indeed, the telescope used for my introduction to solar imaging was sited in Spain and accessed via the internet – so the model is proven. It will be interesting to see whether this new proposal will come to fruition; I wish them well and I’d love to be able to take part, but I’m simply not in that league. In passing, the proposal is labelled Dar Al-Falak which translates as House of Astronomy, and which inspired the title of this post.

I ought to confess that I did spend some money before the end of the day. There was a stand with meteorites for sale and I simply couldn’t resist. I bought a small fragment of the Campo del Cielo iron meteorite (£8/€9) and a teeny, tiny fragment of lunar meteorite NWA11273 (a feldspatic breccia, £14/€16). Next stop, a rocky meteorite and maybe something from Mars? I also bought enough solar viewing glasses for a whole primary school class in preparation for my next school visit; one stall associated with a major astro supplier asked £69/€79 for 25 (!) but I found another stall, run by a lovely chatty couple, who gave me 40 for £30/€35 – yes please 😊

* The book spin-off (Pan Books Ltd, London, 1979) was based on the original BBC Radio 4 series of the same name which ran from 8th March 1978 to 12th April, with subsequent series to come later. I remember listening to this late-night innovative radio play with rapt attention, along with my wife and a couple of friends in a bedsit in Leicester. (One of those friends went on to become a professional astronomer, spending years working on the IRAS infra-red telescope – forerunner to both the Hubble and the James Webb space telescopes.)

# Other companies are available, like Altair Astro from whom I’ve bought all four of my CMOS astro-cameras and one of my telescopes (- I’ve mentioned them in previous posts), and so many more.

Leaving the Milky Way behind: galaxies far, far away

"Space is big. Really big. You just won’t believe how vastly hugely mindbogglingly big it is." [i]

This is the fourth and final image-rich post in a series within which I hope to share my progress in astrophotography; the first is here, the second is here and the third here. I decided to write these posts as a means of taking stock of what I’ve achieved in the years since taking up this challenging hobby in my mid-60s. There’s nothing like writing about something to sort out one’s thoughts. The 'backstory' to this current short series may be found spread through several earlier posts: they'll be obvious if you peruse the blog. An alternative to reading those would be to watch a recording of the talk I gave in January 2025 which summarises the earlier stages of my journey: there’s a link to the YouTube capture in the first paragraph of ‘Climbing over Failure’. Following the pattern of my first three posts in this series, what follows is a collection of my images; the captions will provide additional information. Their quality varies simply because my equipment, software and associated proficiency and skill have evolved over time.

The type of astronomical target I’ll introduce here are galaxies: edge-on, face-on, elliptical, spiral – barred or unbarred – and lenticular; large, small and dwarf; near-neighbours and far-flung; isolated or clustered. The variety is impressive, but not as impressive as their sheer beauty. I’m still awed by the fact that modern amateur equipment is able to reveal these giant but exceptionally faint objects from my garden, even in the presence of light pollution. Trillions upon trillions of stars illuminating the universe. Thus far, we have covered distances ranging from a few tens of light-years (ly) through to a thousand light-years or so as we’ve considered binary star systems, star clusters and nebulæ. Now we must talk in terms of millions – even hundreds of millions – of light-years. The light from the more distant galaxies shown in the images below began its journey to my garden near the start of the Mesozoic Era, during which dinosaurs appeared and moved through forests of early conifers, and the ancient continent of Pangaea was breaking up under the action of tectonics. Indeed, even the nearest of our galactic neighbours – Andromeda and Triangulum – are far enough away that the light from their constituent stars had been travelling across space for more than 2 Mly before being captured by my astrophotography setup.

One more thing I ought to mention in this introductory section is the fact that the concept of a ‘galaxy’ as we now understand it wasn’t established until the twentieth century. They had been observed before that; indeed, the first recorded observation of Andromeda (by Abd al-Raḥmān al-Ṣūfī) dates from 964 AD. For most of the millennium that followed, what we now know to be galaxies were classed as nebulæ. The famous ‘don’t-bother-looking-at-these-because-they’re-not-comets’ catalogue began in 1774 by Charles Messier, eventually included 39 diffuse objects which are, in fact, galaxies. Until the work of Henrietta Leavitt in 1912, which was built upon by others in the following decade and then encapsulated and explained in 1923 by Edwin Hubble, no-one could say definitively that they were distinct bodies far outside our own galaxy.

Let’s start with our nearest-neighbour galaxy, Andromeda, listed as M31 in Messier’s catalogue. It’s a barred spiral galaxy some 2.5 Mly away and a constituent of our local group of galaxies. There are approximately one trillion stars in Andromeda, compared to about 400 billion in the Milky Way. It’s close enough to the Milky Way that our mutual gravitational attraction is drawing the two galaxies together; there is an approximately 50% probability that they’ll merge [ii] in a few billion years to form a large elliptical galaxy. Indeed, current models suggest that Andromeda is itself formed from the merger of two galaxies – one being significantly smaller than the other.

Taken together, the three images of M31 illustrate the evolution in my astrophotography equipment and image processing. On the left immediately above is the first image I generated of Andromeda; it’s still one of my favourites as it shows the dust lanes nicely, a couple of dwarf companion galaxies and even an active star-forming region. On the right is an image generated by the pet robot I introduced in my previous post. At the top, on its own, is an image derived from the same data using a different processing method – the dust lanes still show up well, but the noisier outlying regions of the image are de-emphasised and the visibility of the foreground stars is greatly reduced. 

Although the third largest galaxy in our local group (after Andromeda and the Milky Way) the Triangulum galaxy contains only about 40 billion stars. Thus, despite its closeness – it’s 2.7 Mly away – it appears far smaller than Andromeda in the 1.4° x 1.4° frame of my setup. This is one of a great many targets I really ought to revisit as the image is quite noisy: as I recall, unexpected clouds appeared after only a couple of hours; c’est la vie.

While we’re on the subject of galactic-scale mergers, this pair of galaxies, M51a and M51b, are observed doing exactly that. The larger of the two, M51a (the Whirlpool), is a little smaller than the Milky Way; they are both approximately 24 Mly away, with M51b sitting behind M51a from our perspective. Current models suggest that M51b has already passed through M51a once before being pulled back through to its current position. There is evidence of the ongoing merger visible even in my amateur image: there is, for instance, an evident ‘bridge’ of material stretched out between the two, and the spiral arms are distorted. This process of merging may take another one or two billion years to complete.

On a more modest scale, the two pairs of galaxies shown above are also interacting, though not obviously merging. On the left is a pair of galaxies seen edge-on which are about 30 Mly away. The larger/brighter one is called the Whale, NGC 4631; notice its pup just beneath – a dwarf galaxy rather like those associated with our Milky Way. Above left is a smaller galaxy (the Hockey Stick/Crowbar, NGC 4656/57); even in my amateur image one can discern a distorted shape to one side – this is ascribed to a gravitational interaction with the larger Whale. The blue tinge to its distorted lower arm comes from the presence of a region of intense star formation – perhaps caused by the gravitational interaction. In the right hand image we have a pair of interacting galaxies 59-60 Mly away but only ~ 150 kly apart. (Unfortunately, the information available online is sometimes contradictory but I have tried to sift out the more reliable information.) As with the other pair, their gravitational interaction has distorted their shapes. It’ll be hard to make out in a blog post unfortunately, but above the brighter of the two (NGC 3718, image centre) is a group of very much more distant galaxies – Hickson Group 56. They are ~400 Mly away!

My very first galactic targets were this circumpolar [iii] pair: Bode’s galaxy (M81) and the Cigar galaxy (M82) which are both near The Plough. Bode’s, named after its discoverer who was (you guessed it) Herr Bode, is a spiral galaxy seen at an angle. The Cigar galaxy is pretty much edge-on; it has a distinctive red-coloured dust lane which obscures the galactic core. Both are approximately 12 Mly away. My very first attempt to capture this pair came before I was able to guide my telescope and the result was lamentable: I was barely able to discern the core of Bode’s galaxy, let alone any details of the spiral arms etc.

From pairs to triplets. On the left the Leo Triplet of spiral galaxies – which may be seen within the constellation of … Leo. Their orientation with respect to our perspective varies from edge-on to near full-face; all three are ~35 Mly away. The image on the right shows another triplet, this time appearing to be in the constellation Draco. The galaxies are considerably further away from us (112, 123, 140 Mly) and therefore appear much smaller; despite their separation from one another they are still regarded as being within an identifiable group.

At ~24 Mly away, the spiral galaxy M106 is almost ten times the distance to our nearest neighbour, Andromeda. However, it’s about the same size and luminosity as Andromeda and therefore shows up nicely in this back-garden image. Apart from its intrinsic beauty, I love the fact that so many other, more distant galaxies appear in the frame: it astonishes me still, after several years of astrophotography, that there is so much to see within every tiny patch of the night sky. This is photo-bombing on a cosmological scale.

I have only ever attempted one mosaic in the course of imaging galaxies and galactic groups and this is it: Markarian’s Chain (after Armenian astronomer Benjamin Markarian). The group comprises eight galaxies at distances of between 50 and 60 Mly. There are, however, another 18 galaxies appearing in this 1.9° x 1.4° frame: 26 in total!

Not to be left out, other than in terms of adding a lot more words to an already long post, I finish with images of individual galaxies that simply caught my imagination at a time when I could see them for a decent amount of time from my garden. Each one beautiful in its own right.

For another astrophotography blog post to emerge I need more clear nights. Sadly, the past two Autumns have been characterised by clouds – a consequence of climate change perhaps – and I must practice the virtue of patience 😉

Endnotes:
[i] ‘The hitch-hikers guide to the galaxy’ by Douglas Adams (Pan Books Ltd, London, 1979). The book was based on the original BBC Radio 4 series of the same name which ran from 8th March 1978 to 12th April, with subsequent series to come later. I remember listening to this late-night innovative radio play with rapt attention, along with my wife and a couple of friends in their bedsit in Leicester. (One of those friends went on to become a professional astronomer, spending years working on the IRAS infra-red telescope.)
[ii] I much prefer ‘merger’ over ‘collision’. Whilst the latter makes for good headlines, it really doesn’t convey the process: there may be some individual stars that collide, but the spacing between stars is such that direct collisions will be relatively rare. That’s not to say there won’t be dramatic consequences; gravitational interactions will disrupt both galaxies for many millennia, including generating compression fronts in gas/dust clouds that will lead to the formation of a new generation of stars.
[iii] By circumpolar I mean that they are close enough to the celestial pole that they can be observed all year. (The range that is ‘close enough’ depends on one’s latitude; for my garden at 51° N there are quite a few constellations – Ursa Major/Minor, Cassiopeia – and nebulæ and galaxies that fall inside the definition.)

Clustered

This is the second in a planned short series of image-rich posts within which I hope to share my progress in astrophotography; the first, on binary star systems, is here. Although I’ve been a stargazer since my childhood, this more serious-minded hobby started two or three years after I retired and has progressed haltingly in the six or seven years since. Now, as I approach my mid-seventies, I’d like to take stock of what I’ve achieved and there’s nothing like writing about it to sort out one’s thoughts.

The advent of being able to capture images of star clusters dawned when I finally managed to use plate solving methods to find and identify specific targets and then employ guiding to lock onto them for long exposures. Plate solving is, in essence, a little like using the features on a map to help one navigate to a destination; in this case the map is of star positions and it’s my laptop doing all the work. The plate solving software uses an image of whatever the telescope-astrocam is ‘seeing’ and from the relative positions of the stars in that image calculates what bit of sky the telescope must be pointing at. From there it’s a simple task to work out what correction to that direction is needed to get to the designated target. Indeed, within the software I’m currently using (SharpCap – other packages do similar things) it’s then possible to use the correction identified automatically to slew the telescope to the right direction. However, the Earth is still rotating beneath the night sky so our target will progressively drift off centre unless the telescope is moved in the opposite sense. (A setting-up process called Polar Alignment is a prerequisite for all this; the telescope’s mount is tilted to the observer’s latitude and aligned to the Celestial Pole – near Polaris.) This is where guiding comes in. A small secondary telescope and astrocam is used with appropriate software (I use PHD2) that locks onto the position of stars in its field of view and controls the motion of the telescope’s mount such that they stay in the same position: in other words, it ensures that the telescope accurately tracks the stars. Now we’re in a position to capture objects for extended periods of time rather than rely solely on polar alignment and the need to add together (stack) multiple images of only a few seconds duration. I’ve written about these steps in an earlier post, here.

What follows is a set of images showing the star clusters I have imaged thus far. The quality is mixed, to say the least, which is exactly what you’d expect given the continuing – indeed, never-ending – learning curve I’m on. There are two very distinct types of star clusters: globular and open. The names say it all really, globular clusters comprise groups of stars in a spheroidal arrangement – a ball of stars if you will. Open clusters comprise a group of stars with a separation large enough that each of them can be resolved … assuming they are bright enough to be seen at all. The one thing they have in common is that they exist and orbit within the Milky Way as a group; they are gravitationally bound to one another.

On the left is the best I could do with my first telescope – as described in the previous post; it shows the brightest star in the Pleiades and its near-neighbours. I have inverted the image, which is akin to creating a negative of the sort used by astronomers before digital cameras; it can make it easier to pick out the fainter details. The numbers shown refer to the apparent magnitudes of the stars – a term I outlined in the previous post when discussing brightness. On the right is a more recent view of the entire visible open cluster, Alcyone is central and about 1/3rd down from the top. This is high on my list for a return visit when the conditions are right since it’s travelling through a cloud of dust and gas and the cluster’s members illuminate it at a faint level. I have written at length about the beguiling Pleiades in an earlier post, here.

There seems to be nothing astronomers like better than giving particular groups of stars a descriptive name. The tendency began, I suppose, with the classic constellations – most of which comprise stars not actually held together by gravity but merely ‘lined up’ in the view of the observer. Thus, the Pleiades or any of the clusters shown here would be a defined cluster from whatever viewpoint one might have within the Milky Way but the Plough, for example, only has that shape when viewed from our solar system – it is an asterism. Making out why the above open cluster is called the Pyramid is challenging, so I have included an image on the right which might help 😉.

My final open cluster is called the Beehive – a name that continues to evade explanation to my mind. Although not visible to my setup, there are probably about 1,000 stars in the cluster in total. Its more formal designations include M44 or NGC2632. The ‘M’ denotes the eighteenth century astronomical catalogue begun by Charles Messier, who devoted much time and effort in the compilation of a list of ‘fuzzy’ objects which were not comets. ‘NGC’ stands for New General Catalogue of Nebulæ and Clusters of Stars, although the term new is relative since the catalogue and its supplements were put together in the late nineteenth and early twentieth centuries.

M56 is an interesting globular cluster in theat the stars have a particulalrly low metallic content (compared to our Sun for example). This suggests that the stars are unusually old: few new stars incorporating the heavier elements released in the death of earlier-generation stars. In addition, the cluster is moving counter to the overall rotation of the Milky Way and that suggests that it might have form outside our galaxy and then been captured at some time in the past.

M92 is a globular cluster which has a mass equivalent to ~330,000 Suns. Like many globular clusters its metallicity is relatively low, leading to estimates of its age in the region of 11 billion years.

M3 has a similar morphology to M92 but a higher mass (~½ million Suns) and although still low by galactic standards, its metallicity is a little higher than M92’s. It sits quite a long way above the plane of the Milky Way, which sets it apart. M3 contains an unusually large number of variable stars.

M13, the Hercules cluster, is arguably the most stunning globular cluster visible from the northern hemisphere. It probably has as many stars as M3, but is far closer to us.

The next post I plan to write in this series considers parts of the Milky Way which require us to go up in scale. Indeed, the targets won't all fit into my expanded field-of-view so we'll be viewing specific regions of them. These are the nebulæ: vast clouds of dust and gas. However, the idiosyncratic naming beloved of amateur astrophotographers will continue unabated.

There are several earlier posts which will give you the 'backstory' to this current short series. They'll be obvious if you peruse the blog. The first one I wrote on this post-retirement hobby of mine was uploaded a little over five years ago and focused on imaging the Moon and planets, as were several that came after. However, an alternative to reading those would be to watch a recording of the talk I gave in January 2025 which summarises the earlier stages of my journey: there’s a link to the YouTube capture in the first paragraph of ‘Climbing over Failure’.

Binary

This is, if I can carve out the time, hang on to my present motivation and avoid the distraction of the many other ‘shiny things’ in my world, the first in a short series of image-rich posts. I’d like to share my progress in astrophotography – a hobby started two or three years after I retired – and in the process to try to order my own thoughts and plans as I approach my mid-seventies. I currently envisage a post on the binary star systems I’ve looked at (this one), a follow-on post focused on star clusters, then a look at stars either in the process of ‘dying’ or via their post-explosion remnants. Somewhere in that mix, most probably in the latter post, I’ll bring in my images of vast clouds of gas and dust, and the shockwaves one can occasionally see within them. All of these astro images relate to sights within our own galaxy, The Milky Way, but the final post I want to write and share will focus on my images of other galaxies ranging in distance from our nearest neighbour, Andromeda, to those at distances large enough that their light took hundreds of millions of years to reach the little telescope in my garden.

We’ll start with binary star systems simply because I have already said a lot about them in posts written early on in my astrophotography hobby. These systems were of the necessarily easy-to-find variety given that my equipment, at that stage, was relatively simple and therefore limited: the Mizar-Alcor system, which is part of the Plough, and the Castor system within the Gemini constellation.

Mizar is one of the stars in the ‘handle’ of the Plough. It’s dimmer companion Alcor can be spotted by the naked eye under suitable conditions (i.e. a relatively young eye and a sky without a lot of light pollution!) and is easily spotted using binoculars. This is arguably the easiest binary system to start with. Add a telescope and entry-level astro-camera into the mix and it’s possible to make out that there are three stars in the system: a closer binary, Mizar A and Mizar B, and Alcor. Indeed, this deceptively simple and easy-to-spot system is even more fascinating because each of those three stars is itself a binary – six stars in total dancing around as pairs within pairs within a pair. Although a teeny bit more difficult to locate, the Castor system has a very similar makeup: Castor A, B and C – each of which is itself a binary. (Almost all binary star systems comprise a larger, gravitationally dominant star and a smaller partner. They’ll rotate around a common point in space, which will be closer to the large star. This is driven by the same physics which defines the barycentre between Earth and Moon, and also the Sun and the rest of the solar system. In the case of the Earth-Moon system, both bodies orbit around a point approximately 4,670 km from the Earth’s centre. I wrote about it here and there’s a useful YouTube animation here if you’d like to know more.)

My next step involved looking for colourful binaries – typically binary systems with a blue, white or yellow partners. The perceived colours are affected by our brain’s interpretation of adjacent points of light, but that doesn’t detract from the beautiful sight. It is unfortunate that at this point in my journey I hadn’t realised just how much the mirrors in my Newtonian reflector telescope were in need of re-alignment and calibration. One day I ought to retrace my steps and image them again, but …

The yellow-blue binary Almach (in the constellation of Andromeda) and Cor Caroli (in Canes Venatici) are two such systems, and very pretty they are too.

There is a caution to offer at this point: not all pairs of near-neighbours in the night sky are binary star systems. Yellow Albireo (in Cygnus) and its blue companion, for example, is definitely a pretty sight. However, the jury is out in terms of whether they are actually a gravitationally linked binary system or simply an unconnected pair of stars moving independently within the galaxy which, for a time, appear as a double when observed from our viewpoint. If there is a gravitational link then it’s tenuous.

Albireo: binary or double?

Having an overwhelmingly bright star in a binary system can be a problem when trying to obtain an image of the pair. Regulus is a good example of this; in order to see Regulus B I had to over-expose Regulus A. This is a good juncture for a working definition of a star’s apparent magnitude (- actually, every celestial object has an apparent magnitude when viewed from the Earth). The magnitude represents the object’s brightness; it’s a logarithmic scale: each step of 1 in magnitude represents a change in brightness of approximately 2½ times (more accurately, 2.515). Although it’s not immediately obvious, the more negative the magnitude, the brighter the object. Thus, the Sun has an apparent magnitude of -27, the brightest star visible from the northern hemisphere, Sirius, has a magnitude of -1.5 and Polaris, the Pole Star, sits at +2. Under good conditions the human eye can see stars as faint as magnitude +5. Regulus A has an apparent magnitude of +1.35 (so brighter than Polaris) but Regulus B sits at 8.1 – the difference in brightness on this logarithmic scale is a factor of over 500!

Regulus A & B (the latter at the 7 0’clock position) in the constellation Leo.

One of the peripheral uses of these images was to estimate the ‘performance’ of my telescope-astrocam combination. All of the above images were captured through a 150 mm diameter Newtonian reflector having a focal length of 1200 mm (Skywatcher 150PL) and an ‘entry-level’ camera (Altair Astro 290c). It was a fun thing to do (certainly for a geek) and it gave me confidence that everything was behaving as it ought to be.

Using the Mizar-Alcor system it was possible to verify that my camera’s field-of-view was indeed very small: only ¼° on its long axis! However, it could resolve objects a mere 0.002° apart. The actual distances shown, 1 lightyear between Mizar and Alcor and 55 light-hours between Mizar A and B, are quite short on the cosmic scale – the nearest star to the Sun, for instance, is over 4 ly away. Neptune is about 4¼ light-hours from the Sun.

Newtonian and beginning astrocam on the left, more recent 'deep sky' setup on the right.

When I started getting deeper into the hobby, buying a shorter focal length refractor telescope (Altair Astro 80EDR, focal length 440 mm with 0.8 reducing lens) and an astrocam with a far larger chip (Altair Astro 533c) – both bought second-hand from people I knew – imaging binary stars became a useful ‘filler’ between long runs on larger and fainter objects like galaxies and nebulae. The images below are all taken with this new setup, which has a square field-of-view of 1.4°. There are binary star systems pretty much everywhere one looks …

Even Polaris is a binary system

Next stop, star clusters.

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P.s. there are several earlier posts which will give you the 'backstory' to this current short series. They'll be pretty obvious if you peruse the list of posts on my blog. The first one I wrote on this post-retirement hobby of mine was uploaded a little over five years ago. 

Climbing Over Failure

On Saturday 18th January I gave a talk at the monthly meeting my local Beacon Astronomy Group (here, or here). I was given a gentle brief a couple of months prior – as befits my very amateur status – by the co-organisers Dirk Froebrich and Tim Long: “Tells us about your journey into astrophotography”. It’s a brief that risks self-indulgence from the speaker; I’m sure I succumbed now and again, for which I apologise the those who came to listen, as well as to those who watch Tim’s recording of the talk. The questions, after I’d stopped talking, came thick and fast. I hope this was a good sign – at least people were listening. There were several more open-ended one-to-one conversations as I was packing up; these continued all the way to the car park. I spotted smartphones capturing the odd slide as well which, again hopefully, tells me that there were snippets of information folk found interesting or useful. All good. More than once I promised to complement the talk with a blog post containing the salient bits and pieces: this is it.

In truth, much of what I’ll include here has already been covered in earlier blog posts; I have been writing about aspects of my retirement hobby since the Summer of 2020. However, it’s probably easier all round to extract, condense and augment that material into one brief post than to expect you to follow a load of links and distil everything yourself. I’ll take you through the slides, including a few screen-captures, like the opening slide above, if that helps us navigate. As is customary, I began with an overview and tried to make the point that, although stargazing and photography have interested me since my early teens in the 1960s, it wasn’t until I retired that I could attempt to marry the two. Indeed, I didn’t add a dedicated camera to my first ‘proper’ telescope for almost a year after buying it; I had an enormous amount of fun simply looking through an eyepiece at the beauty above my head. That first telescope, bought a few months after I retired, reflected the advice to beginners I remembered from an episode of the BBC’s ‘Sky at Night’ programme (- which was broadcast in B&W until I was 17 years old!): it was a 150 mm (6") Newtonian, the Skywatcher 150PL. Had I tried harder to update my knowledge or, better still, talked to a few more experienced amateurs, I might have made a different selection. But, then again, perhaps I wouldn’t …

I know others have succeeded, but when I tried to capture images of what I was looking at using my smartphone, it wasn’t very satisfying.

At this point in the timeline I give huge credit to Dirk Froebrich for the opportunity to experience astronomical imaging at a professional level. Dirk, a colleague of mine before I retired, needed someone to look after the Beacon Observatory during the periods he was away over one particular summer. This was a time when his Citizen Science project ‘HOYS’ was in its infancy – there are many more volunteers and partners now. (This is a wonderful project and I heartily recommend it.) I was trained in the basics of running the observatory remotely from my PC at home and sat through quite a few clear nights following the observation script I had been given. I confess to being little more than a ‘trained monkey’ at that point, and I know I made more mistakes than I ought, but I did collect usable data which found its way into a full-blown research paper. I was hooked.

My first dedicated astro-camera was a simple ‘entry-level’ colour model, the Altair Astro 290c, and with it I managed to image all the planets other than Mercury (which I can only ever see through binoculars from an upstairs window due to surrounding trees, houses and so on). I could also image bright/easy-to-find individual stars and a few binary star systems. When trying to image the Moon or Sun (using homemade solar filters – take care!) the limitations of my little astrocam were immediately apparent: it enabled great images, but of only a small portion of these larger targets.

The field of view, FoV, from my reflector telescope and astrocam combination is indicated by the yellow rectangles shown in this smartphone-captured image of the Plough (part of the constellation Ursa Major). This was adequate for binary stars and planets but less so for the Moon and Sun and far too restricted for larger targets such as nebulæ and nearby galaxies: the Andromeda galaxy, for example, covers five times as much of the sky as the Moon (- although it’s so faint that we don’t see it sitting beyond the foreground stars of our own galaxy, the Milky Way). 'FL' in the light blue insert above refers to Focal Length by the way.

Even relatively simple astrocams (or DSLR cameras) need specialist kit and software if one is to gather imaging data successfully. The tripod and mount on which the telescope sits must be able to compensate for the Earth’s rotation: to keep pace with the stars as there appear to move across the sky and thereby to keep the chosen target in your system’s field of view. A key first step is to be able to polar align the mount, which means aligning it to the celestial pole – near to Polaris. I mostly use a Skywatcher HEQ5 mount. Beyond that, software is needed to run the camera and thereafter to process the exposures collected.

For pre-planning and target identification I use Stellarium and Carte du Ciel on my PC, along with useful tools such as those found here, here and here. Useful phone apps include SkyMap, Lunar Map HD and Stellarium along with your favourite weather apps (I use the UK Met Office app alongside ‘Weather & Radar’). For capturing data from my astrocam I use Sharpcap and in order to process that data through to a final image I’ll typically use packages like Autostakkert, Registax, Photoshop / Affinity Photo2 and PIPP. A quick online search will lead you all of these. There are a great many ‘tutorials’ on YouTube, enough of which are sufficiently useful to get you started; better still, join your local amateur astronomy club and tap into the expertise of more experienced people. I’m a member of two that meet in my part of the country, and although I can no longer attend meetings in person I can nevertheless ask questions – and sometimes answer them – via social media, typically Facebook.

There’s one important aspect of all this I’ve yet to mention: the need to mitigate the effects of atmospheric turbulence. The higher the magnification, the more your target will appear to ‘wobble’ as it’s distorted by changes in the atmosphere; it’s the same issue that leads us to talk about the twinkling of stars. The way forward is to use a statistical approach: a method referred to as ‘lucky imaging’. We collect many individual exposures (hundreds, often thousands, using Sharpcap in my case) pick only the best, perhaps the best 10-20%, and then stack them (integrate them in essence; this is where Autostakkert comes in) to generate a decent image. This may be sharpened, colour-balanced or even colour-enhanced, labelled and so on using packages such as Registax and AffinityPhoto.

So far, so good. We still have the issue of a narrow field of view, FoV, and the matter of locating those fainter objects like galaxies and nebulæ that we can’t actually see.

I solved my immediate FoV problem by buying a telescope having a shorter focal length (Altair Astro 80EDR to complement the Newtonian) and an astrocam with a significantly larger detector chip (Altair Astro 533c). With an optical add-on called a reducing lens, this enabled me to increase my FoV to a whopping 1.46 x 1.46°. Whilst a huge improvement, this still represents about as much of the heavens as you can cover with your thumbnail held out at arm’s length: there’s a lot to see up there!

So-called GoTo mounts help circumvent the issue of navigating to faint objects, although I confess to having only modest success using the default control pad that comes with them – especially when limited to my original narrow FoV. I now rely on using Carte du Ciel, which controls my Skywatcher HEQ5 telescope mount from my laptop via ASCOM-EQMOD software … and a game-changing process called plate-solving. The beauty of plate-solving is that the various software packages offering it can use an image of whatever patch of sky you’re pointing at and employ the pattern of the stars present to identify exactly where you are. Integrate that utility within a program like Sharpcap (or APT, or …) and it becomes straightforward to designate a target within Carte du Ciel, which will slew the telescope to somewhere in its close vicinity, then use the plate-solving utility in Sharpcap to refine your targeting.

Having navigated to our target object, with a properly polar-aligned telescope+astrocam combination offering a suitable field of view, we can begin taking the longer exposures necessary for fainter objects. Depending on the mount’s alignment and the quality of its tracking motion one might expect to achieve exposure times of the order of ten seconds or so. It’s still necessary to collect many frames and then to stack them, although the software for this is somewhat different to that typically used in the context of ‘lucky imaging’. I use Deep Sky Stacker, DSS, for this. The image above, unfortunately in monochrome rather than colour due to an error on my part, is derived from 132 4s exposures. In addition, calibration files now become desirable in order to avoid problems with electronic camera noise, bits of dust in the optics etc. – these may become noticeable for longer exposures. Atmospheric turbulence is still present of course, but with exposures very much longer than those typically used for solar system ‘lucky’ imaging, we have by default averaged these distortions. (Thus, light from stars will appear to be spread across several pixels.)

The next important step is to increase exposure times from seconds to minutes. Even with excellent polar alignment and a good tracking mount this isn’t practicable without the use of guiding. In essence, one fits a small secondary telescope, the guidescope, to the main one such that it’s pointing in the same direction. A more modest camera is fitted to the guidescope (ideally monochrome, but that’s not essential) and this is connected to the laptop and to the tracking mount. Using a piece of software called PHD2, which apparently stands for ‘push here dummy’ v.2, our guidescope and camera may be set up to lock onto the positions of a number of the stars in its field of view – meaning that the tracking mount’s position can be corrected in real-time. In theory, and mostly in practice, this means that we’re now safe to use exposures running to hundreds of seconds.

In the screenshot above you’ll notice the circled stars that are being used; there’s a ‘target’ on the right illustrating the scatter in position around the designated centre – it’s calibrated is seconds of arc (one arcsecond is a sixtieth of an arcminute, which itself is a sixtieth of a degree). The interesting bit is the plot at the bottom: this shows the error in Right Ascension (RA, East-West) and Declination (Dec, horizon-pole; see here) – and the corrective pulses sent to the RA and Dec motors in the tracking mount to bring it back to the axis. 

The end result, after lots of image processing which I’m not going to write about here, is an image like this …

My penultimate slide sums it all up:

Whatever else you do, please continue to treat yourself by looking upwards on those beautiful clear nights whenever they come along.