Who doesn’t like Orion and its constituent parts – M42/43, M78, the Witch’s Head, Barnard’s Loop etc.? For many its annual appearance in the night sky is greatly anticipated and will form one of the main astrophotography highlights of the year as it passes across the sky between late November and February. For me a basic afocal image of the Great Orion Nebula for the first time in 2013 marked something of an epiphany, as it demonstrated the power of long exposures in capturing the otherwise hidden beauty and excitement of Deep Sky Objects.
Since taking up astronomy and then astrophotography, I always return to at least one of Orion’s objects each year, initially to see if I could just capture it on camera with my equipment and then to try and improve the image of each target. It’s been a gradual process but I’m pleased to say I’ve usually managed to achieve such improvements over time, which has been both satisfying and often exciting – such is the nature of these objects. Progress almost always resulted from one or more of four developments: new equipment, new software, new techniques and better processing.
Each step was usually small but occasionally a quantum change took place, such has been the case during the past two years: first with the change from DSLR to a CMOS mono camera and then, more recently, learning to plate solve. I was reluctant to change to a traditional CCD mono camera which usually requires very long exposures that, in my opinion, is incompatible with British weather, light pollution and the frequent overhead passage of aircraft where I live between Gatwick and Heathrow airports – if one doesn’t get me the other will, or the low flying helicopters that pass over my observatory throughout the night from nearby Redhill aerodrome!
It was therefore very fortunate that at the same time I wanted to upgrade my camera from a DSLR, the new CMOS sensor technology had literally just arrived on the market. With low read noise and shorter exposures, the ZWO1600MM-Cool mono camera I purchased has been a revolution for me, as well as the entire astroimaging community. Furthermore, the use of narrowband imaging has added a completely new dimension to my astrophotography – apart from the ability to image when the Moon’s about each month and defy light pollution, narrow Ha-OIII-SII wavelengths reveal a whole new world that is both interesting and often dramatic in appearance.
Notwithstanding these developments, I was hitherto hampered by limited integration times of just over two hours (at most) either east or west of the Meridian, until in 2018 I finally mastered (probably that’s overstating my current prowess) plate solving, thereby making integration times literally infinite. All I needed now was clear skies! Despite my enthusiasm for astrophotography, there have been times over recent months when I’ve questioned my choice of hobby and even maybe giving up. Given sufficient funds it is possible to have the most incredible imaging set-up, capable of obtaining equally incredible images – subject to user ability – but if the sky remains cloudy it’s no more than a pile of expensive junk!
Having obtained a very decent LRGB image of the Pleiades on 17th November, armed with the ZWO1600 camera and my new plate solving skills, I decided to take on a project over the winter months. My objective was to obtain one very good image based on a much longer integration time than I’ve previously achieved, acquired by imaging the same object over as many nights as possible during December and January. However, as Robert Burns once put it “The best laid schemes o’ Mice an’ Men, / Gang aft agley,” (translated – the best laid plans of mice and men often go awry). Apart from one evening that fortuitously coincided with the lunar eclipse on 21st January, the skies here remained obscured by cloud from November 18th until January 27th (or 70-days!!!) and I thought my project was scuppered, that is until the other qualities required of astronomy came into play: patience and good luck.
My first image of the Horsehead & Flame Nebulae, 23rd November 2014: William Optics GT81 +FF, Canon 700D (unmodded), SW AZ-EQ6 GT mount, 30 x 90 secs @ ISO1600 + full calibration
The Horsehead and Flame nebulae are traditionally imaged in LRGB colour, indeed my first and subsequent images of these objects have been mostly undertaken in this way (see image above). However, inspired by a narrowband image of these objects I’d seen earlier last year, I too wanted to try and capture these nocturnal bedfellows in narrowband and process the subs using the Hubble Palette technique. Given the aforementioned cloud problem, by the time late January had been reached Orion was already slipping over the western horizon for another year and I thought the project was dead before it could even start, at which point good luck played its part. Starting on 27th January and for three out of the four evenings, the sky cleared and I eagerly launched into the long awaited project.
Unfortunately by now Orion crossed the Meridian about 9 p.m. and most imaging could only be undertaken on the west side, thus limiting each night’s subs again to 2½ hours or less. But with three nights in the bag before inevitably the cloud returned on the 31st January, I had secured 106 x 5-minute Ha, OIII and SII subs or 6 hours 50 minutes of total integration time, at least three times what I had ever previously achieved. The key was plate solving, as each night I could return to exactly the same part of the sky and continue imaging the same objects to the nearest pixel. Having obtained and reviewed the data, it was now time to start processing.
Given the quality and quantity of data obtained I decided to take my time processing and, furthermore, try to use some new techniques to make the very best of the final image. I was particularly keen to tame some of the brighter stars like the blue supergiant Alnitak located uncomfortably close to the Flame and at the same time bring out the interstellar dust that is present in the foreground below the Horsehead and across the lower right quadrant, which becomes evident in the starless processed Ha layer (see image above). It took quite a while but in the end I am very pleased with the outcome, which I think shows all the benefits of longer data integration and the extra care taken processing. The final SHO narrowband version of the Horsehead and Flame nebulae looks a real cracker, perhaps one of my best and has been worth all the patience and additional time taken to show these two objects and the adjacent region literally in a new light.
Needless to say, I’m already thinking about next year, cloud permitting! I hope to return to the Horsehead and Flame for another playtime next winter, in order to acquire more subs with which to build further on the foundation achieved this year by a stroke of luck at the very end of Orion’s annual visit – can’t wait.
| IMAGING DETAILS | |
| Object | (i)Horsehead Nebula (Barnard 33) & (ii) Flame Nebula (NGC 2024) |
| Constellation | Orion |
| Distance | 1,500 light-years |
| Size | (i)8” x 6” & (ii) 30’ x 30’ |
| Apparent Magnitude | +10.0 |
| Scope | William Optics GT81 + Focal Reducer FL 382mm f4.72 |
| Mount | SW AZ-EQ6 GT + EQ-ASCOM computer control |
| Guiding | William Optics 50mm guide scope |
| + Starlight Xpress Lodestar X2 guide camera & PHD2 control | |
| Camera | ZWO1600MM-Cool (mono) CMOS sensor |
| FOV 2.65o x 2.0o Resolution 2.05”/pix Max. image size 4,656 x 3,520 pix | |
| EFW | ZWOx8 + ZWO LRGB & Ha OIII SII 7nm filters |
| Capture & Processing | Astro Photography Tool + PS2, Deep Sky Stacker & Photoshop CS2, HLVG |
| Image Location & Orientation | Centre RA 05:40:57 DEC -02:30:55
Top = North |
| Exposures | 40×300 sec Ha+34×300 sec OIII+32x300sec SII (Total time: 6hr 50min ) |
| @ 139 Gain 21 Offset @ -20oC | |
| Calibration | 5×300 sec Darks 20×1/4000 sec Bias 10xFlats Ha-OIII-SII @ ADU 25,000 |
| Location & Darkness | Fairvale Observatory – Redhill – Surrey – UK Typically Bortle 5-6 |
| Date & Time | 27th, 28th & 30th January 2019 @ +21.30h |
| Weather | Approx. <=1oC RH <=90% 🌙 ½ to ¼ waning |
Surprisingly it is possible to obtain an early glimpse of these objects just before dusk at the end of a night’s viewing in the late summer but the real show begins during November, when they start to appear more conveniently in the darkness of the early evening. With this in mind I recently set out to image the vanguard of the winter night sky, Messsier 45 or the Pleiades, an open cluster dominated by bright blue stars. Located at the ‘front’ of the Taurus constellation, this group of stars heralds the arrival of Orion, perhaps the most spectacular and certainly most imaged constellation of the year, followed by Monoceros, Gemini and Auriga with their own wonderful deep sky objects – but first Pleiades.
Imaging experience to-date with the ZWO camera has shown that 5-minute exposures and unitary settings – Gain 139 Offset 21 – produces a good result with most nebulae targets, however, imaging star clusters and galaxies remains work-in-progress. Whilst tempted to continue with this approach, after reviewing and adjusting the PHD2 settings my guiding has been poor recently, so on this occasion I chose shorter 3-minute exposures to obtain LRGB and Ha subs.
The Heart and nearby Soul Nebula are situated in a busy region of the sky (see above – from Wikisky), which also contains seven open clusters of young stars, as well as the Pacman Nebula and galaxies of Maffei 1 & 2 and M31 Andromeda. The discovery of a bright fish-shaped HII object – known as the Fishhead Nebula IC 1795 or NGC 896 at the edge of the main object – preceded that of the Heart Nebula itself in 1787 by William Herschel. The Heart Nebula has a red glow, a result of intense radiation emanating from a small cluster of large, hot, young (1.5 My) bright-blue stars at the centre known as Melotte-15. The stellar wind and stream of charged particles that flow out from these newborn stars then creates the characteristic heart-shape of the nebula from the stellar dust and hydrogen gas clouds.
The aforesaid object of interest was the Elephant’s Trunk Nebula or IC 1396, a very large emission nebula, which in narrowband shows wonderful colour and detail (HaSHO above). IC 1396 consists of glowing gas illuminated by an open star cluster, broken up by intervening lanes of dark interstellar dust clouds. The ‘trunk’ itself, designated IC 1396A, is the long dark area protruding from the lower edge of the image, spectacularly illuminated from behind by a bright star forming region; the image has been rotated 180o from its natural position. Top right on the edge is the red supergiant Mu Cephei or Herschel’s Garnet Star, one of the largest and brightest known stars in the Milky Way, which in the position of the Sun would extend out to Saturn’s orbit!
WATCH THIS SPACE(MAN) 