Wednesday 3 November 2021

The Desert and the Snow

One of the highlights of living on this corner of East Kent is that it sometimes plays host to interesting or unusual birds, particularly during the passage seasons of spring and autumn. Occasionally you might even get two such visitors in the same week, as happened recently with one rare bird and one not quite so rare (though no less charming). And better yet, neither of them were camera-shy.

Desert Wheatear (Oenanthe deserti)

The first was a Desert Wheatear (above) which spent several days foraging for insects on and around Joss Bay. On the day I went to see it, it was frequenting the edge of the cauliflower field overlooking the bay.

The all-black tail pattern (as compared to the T-shaped pattern of the more common Wheatear) is one of its main distinguishing features, but it can be difficult to see unless the bird is in flight (as shown below).

Desert Wheatear (Oenanthe deserti)

A few days after the Desert Wheatear departed, a Snow Bunting turned up on the stretch of coast between Dumpton Gap and Louisa Bay. Unlike the Desert Wheatear, Snow Buntings are annual winter visitors to the Kent coastline, though I usually have to go out to Reculver to see them.

Snow Bunting (Plectrophenax nivalis)

This little bird was even more confiding than the Desert Wheatear, and not at all fazed by the people walking past and the array of lenses pointing at it. I had to back away from it several times just to keep it in focus.

Whereas the Desert Wheatear was feeding on insects, the Snow Bunting was foraging for seeds, using its beak to break open the husks.

Will we receive any more visitors before the end of the year? It has been a long time since I saw a Shore Lark, and a Lapland Bunting would be very welcome...

See also:

Tuesday 13 July 2021

How I Learned to Stop Worrying and Love the Night Sky

M13 Revisited
Messier 13: The Great Hercules Globular Cluster

"For my part, I know nothing with any certainty but the sight of the stars makes me dream." – Vincent Van Gogh

First: apologies for the lack of posts recently. It turns out that "mapping Mars from my back garden" is a tough act to follow; also, the whole lockdown "thing" tends to put a limit on where you can go (on this planet at least).

On the plus side, I'm pleased to say I recently became a contributing writer for the astronomy website Love the Night Sky. If you're new to the hobby, or coming back to it after a break, this site has all the information you need to get up and running. Unlike many other astronomy-themed websites and YouTube channels (which tend to obsess about getting the perfect astrophoto with little or no information about the object being photographed), the emphasis here is on learning and observing: helping you find your way around the night sky, while enriching your experience with scientific and historical context. I've been observing for years, but it's that sense of there always being more to see and more to learn that keeps me coming back to the eyepiece again and again.

My first three articles (with more to follow) are available via the links below, covering some of the finest deep-sky objects you can see though a telescope. Each article explains what the object is, when to see it, how to find it, and what you can expect to see through telescopes of different apertures, as well as links to other sources of information.

M13: The Great Hercules Globular Cluster (as shown in the image above)

All three of these objects are visible on summer nights, and you don't need a large telescope to see them. So, if the sky is clear and the stars are out, why not grab a pair of binoculars, turn your lights off, and enjoy the view? I could say more, but a certain very famous professor has already said it for me:

"Look up at the stars and not down at your feet. Try to make sense of what you see, and wonder about what makes the universe exist. Be curious." – Stephen Hawking

UPDATE: More articles now available, as linked below:

Remember: a telescope doesn't take up space; it gives you space.

Thursday 12 November 2020

Mars 2020

If you'd told me twenty years ago that I'd one day make a map of Mars compiled from images taken from my own back garden, I wouldn't have believed you. Even six years ago - the last time I had a good look at Mars - I probably would have been doubtful. Back then I was using a 102 mm achromat, and while I was able to identify Syrtis Major and the polar cap through the eyepiece, seeing anything more than that was beyond my capabilities.

The 2018 Mars opposition took place a few months after I got my 254 mm reflector (an Orion XT10 Plus), but an unfavorable southerly declination and a global dust storm meant I couldn't see much more than a shimmering yellow blob (albeit an impressively large blob).

As you've probably noticed, this year's opposition has been much more favourable for northern hemisphere observers. I started taking test images in early September (using a Tele Vue 2.5x Powermate to boost the XT10's focal length to 3,000 mm), and it was while experimenting with my ZWO ASI120MM Mini camera that I had my first stroke of luck. I bought this camera to use for autoguiding during long-exposure astrophotography, but it also functions well as a highly sensitive monochrome planetary imager, capable of capturing significantly finer detail than my Canon 80D DSLR. By sheer coincidence (I didn't plan it that way), the two cameras have almost exactly the same pixel size, making it relatively easy for me to combine the monochrome and colour data in Photoshop, as shown below:

One downside of using the ASI120MM is the difficulty of getting your target planet to drift perfectly across that tiny 1.2 megapixel chip - and then repeating that feat multiple times (remember, I'm using an undriven Dobsonian). I don't recommend trying this yourself unless you have a very well aligned finderscope, preferably one with illuminated crosshairs. 

Another problem is that switching cameras (and their associated adaptors and software) can take several minutes - long enough for Mars to show an appreciable amount of rotation. One way round this is to capture your colour and monochrome data exactly 24 hours and 37 minutes (one Martian day) apart and hope that neither your sky nor the Martian sky clouds over in the meantime. Another, better solution is to sandwich your colour image set with two monochrome sets and use the WinJUPOS software to merge and derotate the monochrome data; aligning the "bread" with the "filling", so to speak.

I won't go through the laborious process of stacking and sharpening, then registering and merging the data in WinJUPOS and Photoshop, when perfectly good tutorials already exist online (see the links at the end of this post), but if you image Mars regularly over the course of several weeks, eventually you should get enough data to make a map like the one at the top of this post. A run of very poor weather through the middle of October meant my coverage of the region centred on 130 degrees longitude wasn't as good as I would have liked, but hey, in an English autumn you take what you can get. Admittedly, I probably could have done a better job of hiding the vertical seams between the different sections, but the end result was still better than anything I could have hoped to achieve when I embarked on this crazy project.

Another thing you can do in WinJUPOS is to wrap your carefully assembled map back onto a sphere and make a rotation video, as shown below:

Mars Rotation Video

Seeing Mars

This autumn wasn't purely devoted to imaging; I also took time to observe Mars through the XT10, switching between the following magnifications depending on what the atmospheric seeing would allow:

171x (7mm DeLite)
240x (5mm Nagler)
333x (9mm Nagler + 2.5x Powermate)
428x (7mm DeLite + 2.5x Powermate)

And here's my second stroke of luck: while browsing the Cloudy Nights forums, I learned that the Baader Contrast Booster filter (which I bought years ago for the refractor) is also very good at enhancing detail on Mars. It also has a warming effect: without the filter Mars has a pale butterscotch hue; with the filter in place it appears more tangerine in colour, closer to the Mars you typically see in photos.

A stubbornly persistent jet stream meant that the moments of truly excellent seeing I was hoping for were limited to a few fleeting seconds at best (fine for imaging, but not so great for observing), but for the most part the visible detail approximated that shown in the first Canon 80D image above.

Here's a pastel sketch of Mars as it appeared on the night of 21 to 22 October, with Solis Lacus, the "eye" of Mars, at centre stage. This view shows south at the top, as it appears in a Newtonian reflector.

It's important to note that I've greatly exaggerated the contrast in this sketch; even with the Baader filter in place the differences between the dusky southern highlands and the lighter northern plains are subtle. It's also worth pointing out that the detail shown here doesn't present itself all at once. The first thing you notice when looking through the eyepiece is that Mars is very small and very bright (even at the highest magnifications). After a few seconds, as your eyes adjust, the tiny but brilliant South Polar Cap (SPC) should become apparent - although, at time of writing, it has shrunk to about half the size shown above. As most astronomers know, the art of seeing - and I mean really seeing as opposed to just looking - is a skill that requires many nights of practice: the first time I looked at this region of Mars (in September), I could immediately tell that the southern hemisphere was darker than the north, but it took a few minutes before I realised that Solis Lacus was staring right back at me. When I looked at it again in October, it was obvious straight away. Over the last couple of months I've been lucky enough to see all the major albedo features shown on the map at the top of this post, as well as the hazy North Polar Hood - its subtle blue tinge contrasting with the intense whiteness of the SPC (these cooler hues are best seen without the Baader filter). However, there is always room for improvement; the finer details revealed by the ASI120MM have eluded me so far: I haven't seen Olympus Mons (yet) which is why it wasn't included on the sketch.

At time of writing Earth is now racing ahead of Mars, but the red planet will remain a fixture in the evening sky for a few months to come. For the next opposition in 2022 it will occupy the winter constellation of Taurus, but its apparent size will max out at a more modest 17 arcseconds (compared to this October's maximum of 22.4 arcseconds). In the meantime there's plenty to look forward to with three new missions due to arrive at Mars in February 2021, aiming to advance our understanding of this enigmatic planet:

Hope Orbiter (United Arab Emirates)
Tianwen-1 (China), including an orbiter, lander and rover
Mars 2020 (USA), including the Perseverance rover and the Ingenuity helicopter drone


Which side of Mars will I see tonight - Ade Ashford | British Astronomical Association

Monday 20 July 2020

A Very Photogenic Comet

Comet NEOWISE over Viking Bay

"Comets are like cats: they have tails, and they do precisely what they want." - David H. Levy
I must admit, when I first heard that comet C/2020 F3 (NEOWISE) was on course to reach naked-eye visibility, my initial reaction was one of mild scepticism. After all, similar predictions had been made about comet C/2019 Y4 ATLAS (which promptly disintegrated) and comet C/2020 F8 SWAN (which also fizzled out). However, NEOWISE didn't just live up to expectations, it surpassed them - becoming certainly the best comet I've seen since Hyakutake and Hale-Bopp, the two Great Comets of the 90s.

Bright though it is however, NEOWISE (named after the space telescope that discovered it) is by no means a Great Comet like those two. Nor is it the first significant comet of the digital age (that honour must go to the spectacular Comet C/2006 P1 McNaught), but - due to its favourable placing for observers in the northern hemisphere - it's likely to become the most photographed comet in history (at least until the next bright one comes along). This is the fifth comet I've pointed a camera at, and it's easily the most photogenic, even if it did require me to leave the house at some very unsociable hours.

Comet NEOWISE should remain visible for the rest of the month, although it will - barring outbursts - become progressively fainter. At time of writing NEOWISE can be found in the late evening sky below Ursa Major (see the links at the end of this post for finder charts). You don't need a telescope to spot it; if your sky is dark enough it should be visible to the naked eye, and a modest pair of binoculars will give a really good view.

You don't necessarily need a long lens either if you want to try and photograph it (the image at the top of this post was taken with a standard 50mm prime). However, you will need a tripod and some means of operating the shutter without touching the camera (either a timer delay or a cable release). As I was shooting at a high ISO I also stacked multiple images and subtracted dark frames to further improve the signal-to-noise ratio. Here's another one taken at 400mm, showing the characteristic golden dust tail:

Comet C/2020 F3 (NEOWISE)

It's worth making the effort to see Comet NEOWISE at least once before it's gone; after all, it won't return to the inner solar system for nearly 7,000 years.

How to see Comet NEOWISE over the coming nights (Sky at Night Magazine)
Comet NEOWISE dazzles at dusk (Sky & Telescope)

Saturday 13 June 2020

Siril: Old Data, New Tricks

Siril ( is a (relatively) new freeware program for stacking and processing astronomical images. I've been using it for a couple of months now and although I'm still very much in the learning curve stage, I'm already finding it to be significantly better than its freeware rivals.

Shown below is a crop of an image of Messier 33 (the Triangulum Galaxy), compiled from two hours of data and processed in Siril. Move your cursor over the image to see my previous attempt at processing the same data in DeepSkyStacker (DSS).


(The full-size version of this image is available on my Flickr page.) As you can see, the improvement is quite dramatic, particularly in the faint outer spiral arms where a wealth of extra detail is revealed. Siril also does a much better job of preserving the colour information from the original raw files. If you've used DSS to stack raw files you may have noticed that the colours come out very muted (as explained in this informative thread on Cloudy Nights). Prior to using Siril, my workaround was to stack the data again in Sequator (effectively using that as an RGB layer and the DSS output as a luminance layer), which always seemed an unnecessarily convoluted way of going about things considering I'm not a dedicated astro-imager.

So how does it work? Video tutorials and manuals are available online, but here's a quick step-by-step guide (applicable to version 0.9.12) to get you started.

When you install Siril it will create four sub-folders in your Pictures directory, one each for light frames, dark frames, flats and bias frames. Make sure your raw files are in the appropriate folders and from the Siril menu select Scripts > DSLR_preprocessing. (Variant scripts are available if you don't collect darks or flats or some other combination.) You'll need a generous amount of disk space because Siril will create individual fit files for every single raw file - but you can safely delete these once the process is completed (just don't delete your raws!).

A live Output Log window shows the script's progress. It takes between 30 and 60 minutes to run on my laptop (about the same time as DeepSkyStacker).

Upon completion, the script will save a file called in your Pictures folder. This is the linear 32-bit file (if you've used DeepSkyStacker it's equivalent to the autosave.tif file) and it will look excessively dark because most of the useful data is bunched over to the far left of the histogram. At this point I would recommend renaming the file to something more meaningful and keeping it somewhere safe, just in case you later find you've overcooked your histogram-stretching and want to have another crack at it.

The image will require a bit of work before it's ready for processing in Photoshop or whatever your preferred image editor is. Fortunately Siril has all the tools you need under the Image Processing menu.

First, change the Display Mode dropdown at the bottom of the image screen from Linear to AutoStretch or Histogram to get a better sense of the quality of your data. The Histogram display mode (like Equalize in Photoshop) is useful for showing the dark boundaries caused by tracking drift over the course of the imaging session. Draw a box on the image to exclude these dark areas and then right-click and select Crop. (You can always carry out a more precise crop later on in Photoshop.)

Siril image window in AutoStretch display mode

The Histogram preview will also show if there's a light pollution gradient in your image. Remove this by selecting Image Processing > Background Extraction. You can select background samples manually or click on the Generate button to have Siril select them automatically. Then click Apply to correct the image.

Change the display mode back to AutoStretch. The RGB image will now likely have a strong green tint. Remove this by selecting Image Processing > Remove Green Noise... and click on Apply.

Any remaining colour bias can be corrected by selecting Image Processing > Colour Calibration > Colour Calibration. Here you'll need to select an empty part of the background before clicking on Use Current Selection and then Background Neutralisation. Then repeat the process for the White Reference section (this time drawing a box around the brightest part of the image).

Now you're ready to begin stretching the image. Change the preview mode back to Linear and select Image Processing > Histogram Transformation. You may have to magnify the histogram to see where the data is. Drag the Midtones slider to the left and the Shadows slider to the right (making sure you don't clip your data). Click on Apply to apply the transformation. As you're probably aware, histogram stretching is an iterative process and will need to be repeated several times to get the desired result. (Hopefully the preview display modes will have given you an idea of where the data ends in your image and where the noise begins.) For images with complex dynamic ranges (such as the Orion Nebula) you may have to create two separate stretched images (one for the core and one for the fainter outer regions, and carefully layer them together in Photoshop).

Siril histogram window

Other functions on the image processing menu which may be useful at this stage include Colour Saturation (for boosting the colour), Median Filter (for reducing noise), and Deconvolution (for sharpening) - although the latter does take a long time to run. Otherwise, you can export the image as a 16-bit TIF by selecting File > Save as... ready for finishing off in Photoshop or your image editor of choice.

Here's one more example, showing Messier 27 (the Dumbbell Nebula) in Vulpecula. Again, move your cursor over the image to see the original (DSS) version.


(A larger crop of this image is available on my Flickr page.) Detail-wise, the differences are subtle (because M27 is one of the brighter DSOs), but look closer and you'll see that the fainter outer regions of the nebula stand out more clearly in the Siril version. I also prefer the rich blue colour in the newer version. Which one do you prefer?

Tuesday 31 December 2019

2019 in Pictures

A very wet (and unseasonably cold) autumn put a bit of a dampener on 2019, but otherwise it was another good year for photos, with a few surprises along the way...

An old favourite to begin - a Stonechat at North Foreland:

Stonechat (female)

A long overdue return visit to Bossenden to see some woodland birds, including this Coal Tit:

Coal Tit (Periparus ater)

And a Nuthatch:

Nuthatch (Sitta europaea)

A Guillemot (not a penguin) stretching its wings at Ramsgate:

"I'm not a penguin!"

No mistaking this Yellowhammer at Dover:

Yellowhammer (Emberiza citrinella)

More wing-spreading, this time courtesy of a Tufted Duck at Stodmarsh:

Tufted Duck (Aythya fuligula) 

A Pied Crow (of all things) on Broadstairs jetty:

Pied Crow (Corvus albus)

+ 1 Peregrine, -1 pigeon:

Peregrine & Prey

I'd like to tell you I spent hours patiently waiting for a glimpse of this elusive Purple Heron, but it emerged from the reeds only a few minutes after I entered the hide. After catching a couple of fish it flew off - apparently never to be seen again. Sometimes (but only sometimes) I'm in the right place at the right time.

Purple Heron (Ardea purpurea)

The month in which winged insects take centre-stage, while the birds enjoy a well-earned break.
This is the first shot of a Banded Demoiselle I've managed where the wings weren't completely closed:

Banded Demoiselle (Calopteryx splendens) 

X marks the Dragonfly spot:

Hawker Dragonfly

A Snipe at Stodmarsh, photographed from the Reedbed Hide:

Snipe (Gallinago gallinago)

This very charming Grey Phalarope at Birchington was another first for me in 2019. I took a Friday off work to see it (and lucky I did because it was gone by Saturday).

Grey Phalarope (Phalaropus fulicarius)

An shot looking over the cliff at the Kingsgate Sanderling roost:

Sanderling Roost

This might well be the second-most photographed bird in England (after that Cuckoo at Thursley Common), but I never get tired of seeing a Kingfisher:

Kingfisher (Alcedo atthis)

And finally, the obligatory Kestrel, seen here flying off with a tasty meal:

Kestrel with Prey

All the photos on this page were taken with a Canon 80D DSLR and my trusty Tele Vue-60 refractor  - that's right, no autofocus.

Wednesday 30 October 2019

Meet the Galactic Neighbours

What's the most distant object you can see with the naked eye? Unless you live near a dark-sky site (and have exceptional eyesight) the answer is most likely the Andromeda Galaxy. To find it, go outside on a clear, moonless autumn evening and allow a few minutes for your eyes to adjust to the dark. The Andromeda Galaxy is located about midway between the square of Pegasus and the "W" of Cassiopeia.

Andromeda constellation map

You should be able to see a faint smudge of light that increases in size when you look slightly to one side of it. (If you're not sure you're looking in the right place, use a pair of binoculars and you should spot it straight away.) That faint smudge of light takes on new meaning when you consider it's a vast complex of stars and dust and gas 220,000 light years across and 2.5 million light years away. It's also barrelling towards us at 110 kilometres per second, so if you hang around a few billion years it's going to get a whole lot bigger and brighter.

In the meantime we'll have to make do with views like the one below. This is an image I made from an hour's worth of exposures using a Canon 80D DSLR and a Tele Vue-60 refractor (focal length approximately 400 mm):

Andromeda Galaxy

Telescopically, M31 is impressive whatever instrument you point at it, but picking out the kind of detail shown in the photo above is more of a challenge than you might think. On a good night I can see the two dark dust lanes northwest of the core region, and also a vague suggestion of clumpiness in the spiral arms, particularly around the star cloud NGC 206. The two companion galaxies, M32 and the fainter M110, are also easy to spot.

Andromeda and our own Milky Way are the two largest members of the Local Group - a modest collection of at least 50 (mostly dwarf) galaxies occupying a region of space 10 million light years across. Roughly 14 degrees south of M31 is the third largest member of the Local Group, M33 (aka the Triangulum Galaxy). Here's an image I took at the end of August, using the same camera/telescope combination, this time assembled from two hours of data.

Triangulum Galaxy

Although M33 is only little further away (relatively speaking) than M31 at 2.73 million light years it has a very low surface brightness - and is consequently much harder to see. It's also very sensitive to light pollution. Oddly enough I always found this galaxy easier to spot in a pair of 7x50 binoculars than in my 4-inch refractor. Even on a good night it was vanishingly faint.

In the 10-inch Dobsonian it appears as an extended misty patch of light with a tiny star-like nucleus. On a favourable night I can just about make out the two main spiral arms (the northern one is brighter and easier than the southern one). Higher magnification reveals a prominent misty spot 13 arcminutes northeast of the nucleus (visible as a blue blob in the image above), lurking close to an 11th magnitude foreground star. This is NGC 604, one of the largest star forming regions in the Local Group. It's a whopping 1,500 light years across, which is roughly the distance between here and the Orion Nebula.

Both M31 and M33 have been extensively studied by astronomers using the Hubble Space Telescope and, as you might expect, the images are spectacular:

Hubble's high-definition panoramic view of the Andromeda Galaxy
Triangulum Galaxy shows stunning face in detailed Hubble portrait