How I Learned to Stop Worrying and Love the Night Sky

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.

M11: The Wild Duck Cluster

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

M8: The Lagoon Nebula

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:

M80: Globular cluster in Scorpius

M57: The Ring Nebula in Lyra

M72: Globular cluster in Aquarius

M77: Spiral galaxy in Cetus

M76: The Little Dumbbell Nebula in Perseus

M52: Open cluster in Cassiopeia

M37: Open cluster in Auriga

M78: Reflection nebula in Orion

M42 (and M43): The Great Nebula in Orion

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

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:

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

Links

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

How to capture scientific images of Mars - Pete Lawrence | Sky at Night Magazine

Use WinJUPOS to derotate your planetary images - Martin Lewis | Sky at Night Magazine

Imaging the planet Mars - Roger Hutchinson

WinJUPOS download site

A Very Photogenic Comet

"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:

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.

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

Siril: Old Data, New Tricks

Siril (https://www.siril.org/) 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 result.fit 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 result.fit 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?

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.

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):

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.

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

Into the Whirlpool

Ask someone to draw you a galaxy and chances are they'll come back with a spiral shape. Even a small telescope will show you plenty of galaxies (if you know where to look), but how large a scope do you need to see those dramatic spirals? Edge-on galaxies like M82 and NGC 4565 show lots of detail in modest-sized scopes because their light is concentrated into a smaller area, but the majority of face-on galaxies have such a low surface brightness that the slightest haze or encroaching light pollution can render their spiral arms invisible.

There are a few notable exceptions however, and for northern hemisphere observers, the consensus seems to be that Messier 51 (commonly known as the Whirlpool Galaxy) is the best of the bunch. It resides some 25 million light-years away in the constellation of Canes Venatici (the Hunting Dogs), and can be found high overhead on spring evenings near the tail of the Great Bear (Ursa Major).

Here's a photo I took (actually forty-three 90-second exposures, stacked together) in March, showing the spiral very clearly:

M51 & NGC 5195, 28 Mar 2019; Canon EOS 80D + Tele Vue-60 + Vixen Super Polaris

For a larger crop, see the version on my Flickr page.

Sixty-five minutes' worth of sensor data is one thing, but how much of that detail can you actually see with your own eyes? M51 and its interacting companion NGC 5195 are easy enough to spot through even a small scope, but it wasn't until I got the 10-inch reflector that I was able to see them as more than a pair of faint fuzzy blobs. Even then, the detail was elusive, with the dark spaces between the Whirlpool's arms often more apparent than the arms themselves.

My sketching skills are very rusty so it took me three attempts before I got something I was happy with, but here's an approximation of what M51 looks like through a medium-sized scope on a good night:

For this I used the 10-inch Orion XT10 and a Tele Vue Nagler 9mm eyepiece, giving a magnification of 133x.

Depending on the quality of your night sky, you may be able to see M51's spiral with a smaller telescope. I was never able to make it out with my 4-inch refractor (although the two galaxies themselves were obvious), and even with the XT10 I can't always see it, as demonstrated by these excerpts from my observing notes:

19 May 2018 (first night out with the new scope; sky a little hazy)
Not well placed (wrong side of meridian), but both galaxies showed bright cores. Strong hint of spiral arm structure, and a star superimposed over the face of the galaxy (not a supernova!).

10 February 2019 (cold, but not freezing; sky transparency improved considerably once the crescent moon got out of the way)
In a night of highlights, M51 was the undoubted stand-out. After staring at it for a couple of minutes I suddenly realised I could see the spiral arms quite clearly, defined by the dark space separating them. One arm curling out from core region around a foreground star. A magnificent sight at 133x, even though it was still some way from the zenith. With averted vision it started to look like a ghostly monochrome photo.

31 March 2019 (slightly chilly, windy with occasional strong gusts; transparency good, but not up to the standard set on 10 Feb)
Tonight M51 and NGC 5195 had an almost ghostly aspect about them; the spiral arms seemed to fade in and out of existence independently of averted vision. The view wasn’t substantially improved at 240x, other than highlighting some of the brighter areas with a milky glow. 

4 April 2019 (chilly, gusty evening; excellent seeing, transparency improving as night went on)
Best view of spiral structure since 10 Feb; showed particularly well in averted vision. Dark areas between arms just about visible in direct vision. Also found a faint, round little galaxy roughly south of M51 – not plotted in the Pocket Sky Atlas, but later identified as NGC 5198.

(If you're into this sort of thing and you want to read more of my observing notes, I'm in the process of putting them online at https://mskastro.blogspot.com/ )

The visibility of the spiral is very sensitive to sky conditions, so if you don't succeed on one night, try again on another (and make sure your eyes are fully dark-adapted). Patience and persistence are vital. And here's another tip: if M51's spiral still seems maddeningly faint, steer your scope to the other side of the Great Bear's tail and see what you make of the larger (and fainter) spiral galaxy M101. Trust me, when you return to M51 it will seem positively bright by comparison.

So now you have an idea of what it takes to see the spiral in M51, but what about resolving individual stars in this beautiful galaxy? For that I recommend taking a very deep dive into this image by the Hubble Space Telescope...

See also:
Cosmic Challenge: M51's Spiral Arms - Phil Harrington (Cloudy Nights)

Into the Orion Nebula

M42, Orion: Tele Vue 60 + Canon 80D + Vixen Super Polaris

"An unformed fiery mist, the chaotic material of future Suns" - William Herschel, 1789 

Herschel's description (written long before spectroscopy revealed the true nature of gaseous nebulae) could hardly have been more prescient. The Great Orion Nebula (Messier 42) is indeed a cradle of new stars (at 1,300 light years, the nearest star-forming region to our own sun), visible to the naked eye as a misty patch in Orion's Sword on winter nights.

Viewing M42
I'm occasionally asked what it looks like through a telescope: a one-word answer would be "Majestic", but don't expect to see the full extent of the nebula - or indeed the vivid colours that you get in photos like the one above. As with most deep-sky objects, the Orion Nebula rewards careful and prolonged examination. Here's a sketch I made a long time ago (for GCSE Astronomy coursework!) illustrating the typical low-power view through a small telescope under suburban skies:

One telescopic feature you won't often see clearly in photographs is the Trapezium, a tight grouping of four hot young stars whose ionising radiation has helped sculpt the nebula into the shape we see today. In my 4-inch refractor the nebula is nicely framed in a 24mm Panoptic eyepiece (42x magnification) with layers of nebulosity building up to the core. Add in an Ultrablock filter to improve the contrast and the nebula takes on the appearance of a swooping bird of prey. With a 5mm Nagler (200x) under steady skies, a fifth member of the Trapezium is just visible.

So far the weather has only allowed me one opportunity to look at M42 with the XT10, but even under less than ideal viewing conditions it was immediately obvious that the extra aperture had improved the view dramatically. The core region had a strong green tint and averted vision made it so bright that the Trapezium was almost lost in the glare. Lots of finely detailed structure was visible with dark rifts cutting through the nebulosity. The Ultrablock filter wasn't really necessary for such a bright object, but it did seem to increase the overall extent of the nebula, particularly on the northern side.

Photographing M42
For any birders who've made it this far, the Orion Nebula is arguably to astrophotography what the kingfisher is to bird photography, the gateway drug that lures you into a lifetime hobby. (It even comes with its own fish, of a sort.) The image at the top of this post is a stack (not a mosaic) of 108 thirty-second exposures (plus 15 dark frames and 21 flat frames). As I'm still shooting unguided (for now) I've been careful not to choose targets too far away from the celestial pole, so at -5 degrees declination M42 presented the biggest test yet of my polar alignment accuracy. Fortunately the Great Nebula is a forgiving target - you can pull out a considerable amount of detail and colour even with relatively short 30-second subs. If you look closely, some slight trailing is evident, but not enough to spoil the final image.

Processing M42
As I've said before, acquiring all the light-frames (plus darks and flats) is only half the battle; there's still a lot of work to do. The image above was assembled using the freeware program Sequator. Compare it with my first attempt using the more widely-known freeware DeepSkyStacker. The samples on the Sequator website suggest it's optimised for landscape astrophotography (i.e. wide-angle shots in which the horizon is visible), but it seems to do an equally good job for deep sky photography. In terms of workflow, I certainly found it easier to process the stacked image produced by Sequator. As you can see in the mouse-over comparison below, Sequator did a much better job of retaining the detail around the Trapezium area. There's less noise too, although the DeepSkyStacker version shows more of the fainter regions of the nebula.

 

It's also worth noting that Sequator did an excellent job of identifying and removing the light pollution gradient. DeepSkyStacker doesn't cater for this so I used the Light Pollution Removal tool in Noel Carboni's Astronomy Tools Actions set (which, despite having more user control, did on this occasion leave a series of contour lines in and around the brightest parts of the nebula). The Sequator stack did contain some colour noise, but this was easily removed using the Colour Blotch Reduction tool from the same set.

Other pros and cons: Sequator was fast (less than 30 minutes processing time compared to up to an hour for DSS). However, it also left some curious purple "appendages" around some of the brighter stars, as shown in the crop below:

I've seen Sequator described as "stacking for dummies" on one popular astro-forum, but on the above evidence I think it'll be this dummy's image-stacker of choice for the foreseeable future. This is by no means a rejection of DeepSkyStacker, but more likely an indication that I still haven't learned how to get the best out of it.

I like the colours better in the Sequator version too, although that's a matter of personal taste.

Which one do you prefer?

A Journey into Astrophotography

I'll say one good thing for He-Who-Must-Not-Be-Retweeted; he's encouraged me to turn my attention away from this increasingly nonsensical planet and back into deep space*. I've dabbled with astrophotography before (hand-tracking with a 50 mm lens), but mostly I've stuck to the brighter objects like the moon and Jupiter. Long-exposure astrophotography at focal lengths greater than 300 mm requires precise motorised tracking, but it was only after a trip to Astrofest 2018 (and some intensive research) that I figured out a practical and affordable way to go about it.

Here's a picture of the trusty Tele Vue-60 (the same scope I use for most of my wildlife shots) in its latest mode atop the equally trusty Vixen Super Polaris mount (fitted with Skywatcher dual-axis motor drives and an ADM dovetail plate adaptor):

With a field-flattener attached the TV-60 is roughly equivalent to a lens of 400 mm focal length. So far, this arrangement is good enough for exposures up to about two minutes duration depending on the accuracy of my polar alignment. (The Skywatcher handset does have an ST-4 port for autoguiding should I wish to attempt longer exposures in the future.) Here's another angle showing the motor drives attached to the Right Ascension and Declination axes:

Any serious astrophotographers visiting this blog might be shaking their heads at this point and muttering about vignetting and edge-of-field distortion, red sensitivity, thermal noise etc. in much the same way that serious wildlife photographers might mutter about autofocus and aperture control when they see what I'm using. But the point is, I don't get enough clear, moonless nights a year to justify spending the kind of megabucks that others spend on their gear. And, crucially, I can use the same DSLR and the same little scope for multiple purposes (which probably explains why the focuser is starting to look a little worse for wear). And (whisper it quietly) one good photo of the Orion Nebula looks very much like another good photo of the Orion Nebula, no matter where you are on the earth. Unless you have your own observatory equipped with an adaptive optics system, you're probably not breaking new ground.

That's not to say I won't be eagerly imaging the Orion Nebula when I get the chance just like every other amateur, but M42 is a spectacle of the winter sky, so for my first target I chose the globular cluster M13 (because it's big, bright, and not too far away from the north celestial pole):

M13, Tele Vue-60 + Canon 80D (30 x 1 min @ ISO 800)

The long exposure times required to make an image like this turn pinprick stars into blobs of light, giving the false impression that they are almost touching each other. Although direct interactions in globular clusters do occasionally happen (the most likely origin of blue stragglers), the average distance between stars in a typical globular is actually 0.1 to 0.5 light-years, a fraction of the distance between here and Proxima Centauri (4.2 light-years), but still many times the size of our planetary system. This image from the Hubble Space Telescope resolves the core of M13, giving a better impression of the star density. Around 150 globular clusters are known to orbit our galaxy, dipping in and out of the galactic plane in highly inclined orbits. To put that in perspective, M87, the giant galaxy at the heart of the Virgo Cluster, is surrounded by 16,000 globular clusters.

I recently had the pleasure of looking at M13 through a 10-inch telescope and the result was breath-taking (so much so that I completely forgot to look for NGC 6207 - the "little" galaxy visible towards the bottom-left of the image above).

In my 4-inch achromat M13 takes on the appearance of a "grainy snowball thrown against a pane of glass", always on the brink of being resolved but never quite making it, except when averted vision is employed. In the 10-inch scope (at 133x magnification with a 9mm Nagler eyepiece) it was transformed into a vast three-dimensional city of stars, its brighter members glinting like crushed diamonds right across the face of the cluster, with hundreds - perhaps thousands - more revealing themselves in averted vision. The longer I looked, the more impressive it became, as I began to discern chains of stars arcing out from the centre.

M13 is arguably the most spectacular globular cluster visible from UK latitudes, but there are several others which run it close, such as M3 in the constellation Canes Venatici:

M3, Tele Vue-60 + Canon 80D (31 x 1 min @ ISO 800)

Of course, acquiring the images is only half the battle; processing them is an art-form in itself. I'll leave those details for another time as I'm still very much a beginner at this, but if you want to know what software I used, the links are here.

In the meantime, if you ever get the opportunity to look at M13 or any of the other showpiece globulars through a medium to large-sized telescope, I strongly recommend it. Drink in the spectacle, contemplate what you're seeing, and then look at it again. Photographs just can't do it justice.

See more of my TV-60 deep-sky photos on Flickr.


*Famous last words... While I was drafting this post, He-Who-Must-Not-Be-Retweeted announced the creation of SPACE FORCE (I swear I can hear the echo as I'm typing it). It seems there really is no escape from the Tangerine Nightmare.

Answer: "It's a Tele Vue."

The question being, typically: "What's that on the end of your camera?"

As the name of this blog suggests, I do most of my photography with a telescope - a Tele Vue-60 refractor to be precise. What it lacks in autofocus and aperture control it more than makes up for in sharpness and colour correction. It's compact and portable and it doesn't need to be stopped down to hit the sharpness sweet spot. Recently Tele Vue embraced the world of social media and - as part of their ongoing 40th anniversary celebration - they asked if they could feature me on their new blog, in particular why I chose the TV60 and why I've stuck with it over the years. You can read the resulting post here:

http://televue.com/notamnomen/2017/05/02/tele-vue-is-for-the-birds/#.WRC_XNQrL4Y

Three scopes in one: astro-scope, spotting scope and telephoto lens

Astronomers of course need no introduction to Tele Vue, but for those who don't know, they're a Chester, New York-based company founded in 1977 by Al Nagler. Prior to that Al designed lunar landing simulators for the Apollo missions, using his knowledge of optics to create realistic wide-field vistas to aid the astronauts' training.

Tele Vue started out making lenses for large projection-screen televisions, but they've since become renowned for their high-quality eyepieces and telescopes. If you ever get the chance to look through one of Tele Vue's wide-field eyepieces, I highly recommend it. They call it the "spacewalk" experience and with good reason: if, like me, you started out in astronomy squinting through a cheap and cheerful 0.965" eyepiece, the difference is startling. When looking through a Nagler it's as if the eyepiece "gets out of the way", leaving you immersed in the stars (or suspended above the moon if lunar observing is your thing). And if the 82-degree apparent field-of-view of a Nagler isn't enough for you, they also do an Ethos range, which goes up to a whopping 100 degrees.

In the interests of fairness and transparency I should point out that:

a) Other telescopes and eyepieces are available
b) I was not offered any incentive by Tele Vue (financial or otherwise) to contribute to their blog or write this post. I'm just a proud TV-60 owner and I wouldn't dream of parting with it.

See also:
Tele Vue home page
My TV-60 photos on Flickr

Photographing the 2015 Total Lunar Eclipse

Lunar eclipses aren't that rare - certainly not as rare as some uninformed sections of the media would have you believe, but I hadn't photographed one since March 2007, so I stayed up till stupid o'clock the other week to get some images of the so-called Super Blood Moon eclipse. The wind was a little gusty, but fortunately the clouds didn't interfere.

One thing the photos don't convey is just how much the moon dims during totality. (The reason it doesn't go completely dark is because it's illuminated by sunlight refracted through the earth's atmosphere. Or to put that in a slightly more lyrical way, an observer standing on the moon during an eclipse would see all of the earth's sunrises and sunsets compressed into a beautiful ring of light.) The first image in the sequence above (the barely eclipsed moon) was shot hand-held with a 1/1600 second exposure at ISO 800. The last shot (fully eclipsed) was taken on a tripod with a cable release, with the mirror lock-up function enabled; exposure time 1/2 second, ISO 1600. At long focal lengths (400 mm and above), these slow exposure times can be problematic. Shoot for anything longer than about half a second and the earth's rotation will start to smear the image.

So, as is often the case in astrophotography, there's a trade-off to be made. Do you under-expose and increase noise, or do you expose correctly and lose detail? A tracking mount which will correct for the earth's rotation is one way around the problem, but the good ones don't come cheap. Another method (if you find high ISO noise objectionable) is to shoot lots of under-exposed images one after the other, stack them in RegiStax or AviStack to increase the signal-to-noise ratio, and then push the exposure in Photoshop. I did think about doing this, but it was late and I was tired and it seemed like a lot of effort given that I still had several hundred photos from the Camargue to sort through (a post on that is coming soon).

Maybe it's something I'll try for the next eclipse in 2018; or maybe by then cameras will have progressed so much that high ISO noise won't be a big deal... Anyway, to tide us over till then, here's an uncropped view of the eclipse taken at ISO 6400, and carefully pushed in PS to bring out the background stars. A red full moon surrounded by stars; now that's a sight worth staying up for.

PanSTARRS and Other Comets

It was David H. Levy who said: "Comets are like cats; they have tails and they do precisely what they want," but in many ways Comet C/2011 L4 (PanSTARRS) did precisely what was expected of it, in managing (just about) to reach naked-eye visibility, while never coming close to attaining the prominence of mid-nineties wonders, Hyakutake and Hale-Bopp.

Comet C/2011 L4 (PanSTARRS), Broadstairs, March 2013

After two failed attempts to see it, I first caught a glimpse of Comet PanSTARRS through a gap in the clouds on Wednesday 13 March, but it wasn't until the following Tuesday that the sky stayed clear long enough for me to get some images. As this is only the third comet I've photographed - after McNaught (arguably the first Great Comet of the digital age - for the Southern hemisphere at least) and Holmes (arguably the weirdest astronomical object of the digital age) - I was just pleased to get anything at all, but a potentially great comet could be waiting in the wings in the shape of C/2012 S1 (ISON), which will swing through the inner solar system later this year. I must stress the word "potentially" though because ISON might not even survive its close passage to the sun, leaving us with the ghost of what might have been. If comets are indeed like cats, then ISON may yet turn out to be of the Cheshire variety.

Comet PanSTARRS, 13 images stacked in RegiStax

And as if that wasn't enough, make a note in your diary for October 19, 2014, because that's when Comet C/2013 A1 (Siding Spring) is due to make a very close approach to Mars - so close in fact, that the possibility of an impact cannot yet be ruled out. If (and that's a very big "if") it did happen, it would be the most destructive event in the solar system since Comet Shoemaker-Levy 9 carpet-bombed Jupiter in 1994 and could have profound effects on the Martian climate. Either way - direct hit or near-miss - it promises to be quite a show.


See also:
Planetary Society: Comet to whiz past Mars in October 2014
Planetary Society: Will comet Siding Spring make a meteor shower on Mars?

Sir Patrick Moore - A Belated Tribute

The final edition of The Sky at Night to feature Sir Patrick Moore aired last night on BBC 1 (and will be showing again as an extended episode on BBC 4 later in the week), so this seems like a timely moment to share a few thoughts I originally posted on the Sky at Night Flickr group a few weeks ago.


Many moons ago, my mum wrote to Sir Patrick, asking him for advice on what telescope to buy her astronomy-obsessed son, and he very kindly sent one of his famous hand-typed letters in reply, offering his usual brand of no-nonsense wisdom.

Years later, after going on to study astronomy at university, I was fortunate enough to attend one of Sir Patrick's BAA lectures at the University of Kent, in which he spoke about Mars for an hour (without notes). It was the period straight after lunch (a tough time to give a lecture), but he kept the whole audience captivated with his energy and boundless enthusiasm.

And just last month, I was watching The Sky at Night on BBC 4 when I was pleasantly surprised to see one of my photos featured in an item about the planet Mercury.

RIP Sir Patrick, and thanks for everything. You will be missed.

See also:
The Sky at Night on BBC iPlayer (available until Sunday 13 January)
The Sky at Night programme page
BBC Stargazing LIVE (starts Tuesday 7 January)
BBC Sky at Night and Stargazing LIVE Flickr page

Ocean of Storms

At first glance Oceanus Procellarum (the Ocean of Storms) appears to be one of the less interesting regions of the Moon, presenting to the casual observer nothing more than a vast, monotonous plain of dark grey lava, dotted with the occasional impact crater. But look closer and you'll find evidence of ancient volcanism on a huge scale, unlike anywhere else on the lunar surface.

Here's a 100% crop showing the Aristarchus plateau - an diamond-shaped block of uplifted terrain dominated by the dazzling crater Aristarchus and the 160 km-long Schröter's Valley:

Easily visible in a small telescope, the valley is the largest and perhaps most dramatic example of a lunar rille, a sinuous channel cut (a very long time ago) by fast-flowing lava.

Follow the terminator south and you come to the Marius Hills, a complex of some 300 volcanic domes and hills that - through a small telescope - look like pimples on the lunar surface:

Lunar Orbiter 2 photographed the complex from an oblique angle, giving an idea of the relative height of the domes, and a few decades later the Japanese SELENE/Kaguya mission discovered an intriguing dark pit in the area (shown here in a high-resolution image taken by the Lunar Reconnaissance Orbiter).

Incidentally, if you move your mouse over the cropped images you can compare the finished versions with one of the original photos, illustrating the dramatic improvement that image-stacking can make to lunar photography.


See also:
Procellarum: The Biggest Basin?
Shooting the Moon: Lunar Photography with a DSLR and a Small Refractor

Sea, Wind and Fire

I don't make a habit of going out with the camera at 4:30 in the morning and I especially don't make a habit of pointing a telescope at the sun, but this particular shot's been on my mind for a while.

 

Distance to the Thanet wind-farm: approximately 7 miles.
Distance to the sun: approximately 93 million miles.

It may not be as newsworthy as the Venus transit but I was fortunate enough to catch a sunspot group (visible towards the right-hand side of the sun's disc). This is AR1504 (AR standing for Active Region) and it was the source of some significant flare activity recently, as shown in this video from NASA's Solar Dynamic Observatory (SDO).

You'll also notice that the sun is distinctly flattened in this photo. I would offer an explanation, but why go to all that trouble when there's already a perfectly good one available on the excellent Atmospheric Optics website? A warning though before you visit this site: "Checklist" photographers (you know who you are) may be compelled to invest in a brand new set of wide-angle lenses after seeing examples of the full range of weird and wonderful phenomena that can grace our skies.

Photographing Earthshine

I generally try to avoid going back and tinkering with old photos because - as with any creative endeavour, whether it's writing a story, composing some music, or making a film - there comes a point where you have to say, "Enough's enough," and walk away from it. However, I was recently contacted by a production assistant at Popular Photography magazine saying they were interested in using my image "Crescent Moon with Earthshine" for a "How-to" feature in the June 2012 issue*.

The original image was composed back in April 2007 and close inspection shows quite a lot of noise and signs of oversharpening (as well as some obvious artefacts from where the two stacks were spliced together). I've learnt a lot about processing since then - and newer tools have become available - so I decided I could do a much better job if I went back to the source files and reprocessed them from scratch.

For those who are interested in the technical nitty-gritty, the images were taken using a Canon 350D (Rebel XT) DSLR connected to a Vixen SP-102 achromatic refractor (focal length 1000mm). Earthshine (which is the reflected sunlight from the earth illuminating the shadowed part of the moon) is easy enough to capture on camera, but normally results in a severely over-exposed crescent. To retain the detail on the crescent I shot 31 images at 1/60 sec, ISO 200, and to expose the earthshine I took 11 images at 0.5 sec, ISO 800. I then stacked and sharpened these images separately using the freeware tools AviStack and RegiStax, before combining them in Photoshop using a layer mask to create the finished version you see above.

This new "redux" version is a big improvement on the original, and is probably the best I could do given the quality (and quantity) of the original 350D image files. Some flaws are still apparent: the dark band between the earthshine and the crescent is a little distracting and the earthshine itself could be brighter. These are issues that could be fixed by capturing more images at a wider range of exposures - and then combining them using HDR software.

But that's a project for another day...

*And in case you're wondering, yes they did use it, and yes they did pay me.

See also:
Shooting the Moon: Lunar Photography with a DSLR and a Small Refractor
Earthshine (NASA Science)
Planetshine (Wikipedia)

Venus and the Moon

If the weather is clear later today (which doesn't seem very likely at time of writing), Venus and the crescent moon should make a nice pairing in the evening sky. Venus of course has been at its brilliant best in recent months, so brilliant in fact that you can see it in daylight if you know where to look. It helps if the sun is shielded by a building or a tree, but the real trick is getting your eyes to focus to infinity while staring at an apparently featureless blue sky.

The moon and Venus, June 2007

Your chances of seeing Venus during the daytime are greatly improved if something prominent like the Moon is nearby, as it was during the occultation of 18 June 2007. The image above was taken at half past four in the afternoon, shortly after Venus emerged from behind the moon's limb.

Venus will continue to dominate the evening sky for the next month, before passing in front of the sun's disc on June 5th-6th (the last such transit until 2117!).

Introduction

First off, I don't claim to be an expert on birds or photography, so if I confuse a silent Chiffchaff for a silent Willow Warbler (or vice versa), or get into a muddle over crop factors then please let me know and I will endeavour to correct my mistake. (Constructive comments are always welcome.) However, I do like to think I've learned a few tricks over the last few years, so perhaps you'll find some of these posts interesting and maybe even useful on occasion.

I've been reluctant to start a blog of this nature before now because a) I've never been one for keeping a diary, and b) having maintained a Flickr page for several years I've always been of the opinion that a good photo should speak for itself without any distracting words. However, I'm often asked how I got a particular shot, how I processed it, or indeed what that thing is on the end of my camera, so hopefully this blog will go some way towards answering those questions.

As there are already a number of excellent websites and photography blogs covering the wildlife in and around East Kent (some of which I've linked to on the right), I don't intend to simply replicate what's already out there. So, as well as describing what I've seen in a given week, I'll also be writing about how I take and process my bird photos, as well as occasionally venturing beyond the Earth and into the realm of astrophotography.

The common thread linking these strands is that almost all of the photos you'll see on this blog were taken with a Canon DSLR mounted at the prime focus of a telescope; the birds and insects with a Tele Vue-60 apochromatic refractor (focal length approximately 400mm), and the moon and the planets with a Vixen SP-102 achromatic refractor (focal length 1000mm and - with a Powermate - 2500mm). There are pros and cons (and misconceptions) to using a telescope instead of a dedicated camera lens - some of which I'll be talking about in future posts - but I have to admit there is something quite appealing in being "that guy who shoots with a telescope" as opposed to being just another photographer with a big white lens.

Plus, telekilnesis has a nice ring to it, don't you think?