Forbidden Fruit

September 21, 2016 by grahamrob in Autoguiding, Deep Sky Objects, General Astronomy, Imaging, Software and tagged DSO Imaging, Guiding, Messier Objects, Nebulae, Photography | 3 Comments

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Soon after embarking on my astrophotography adventure just over two years ago it became apparent that after getting the basics right – polar & star alignment, focus, image capture etc. – the Holy Grail of imaging is increased exposures times, thereby collecting more of those elusive photons that have travelled across the Universe. The first step to achieving this goal is tracking, which since purchasing my AZ-EQ6 mount in 2015 I have been successfully improving over time, on a good day achieving 180-second exposures and from time-to-time resulting in some decent images. However, the light from DSOs is often very feint and can require much longer times, which is easier said than done.

At the same time as acquiring the aforesaid mount and a William Optics GT81 telescope I also purchased a William Optics 50mm guide scope, with which I intended to start guiding and thus push exposures above my 3-minute barrier. Despite these aspirations, through a combination of events and my unease about the apparent difficulty of guiding, the guide scope has remained unused – until now. Having recently purchased a dedicated Starlight Express Lodestar X2 guide camera, I have finally been emboldened enough to give it a try.

Starlight Express Lodestar x2 Guide Camera can be used either via the mount’s ST4 port or via ASCOM and the computer for pulse guiding.

I initially struggled to set up the guide scope and get the guide camera working together. In particular obtaining focus proved very difficult; like the GT81 the guide scope focus turns out to be achieved within a very short distance that is measured in fractions of millimetres, which in this case required the insertion of an extension tube.

Reminiscent of the Space Shuttle on its Boeing 747 transport plane! The William Optics 50mm guide scope + Lodestar X2 guide camera neatly mounted atop the GT81 imaging scope using the integral rings.

Thereafter the big challenge, which I had previously avoided, was to start using the very popular PDH guiding software; Push Here Dummy (PHD) is named tongue-in-cheek by its original creator Craig Stark and is an amazing but somewhat intimidating piece of software.

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The principle is simple – find a star within the FOV and use it as a fixed reference point from which to assess and then correct small tracking errors in order to achieve better tracking, which thereby maintains pinpoint accuracy and enables longer exposure times, thus avoiding trailing of the sky and the objects being imaged. Its use is regarded as something of a dark art but I have finally grasped the nettle with some success. After months of clouded skies followed by an almost fatal equipment failure (see here for more), a period of exceptionally good weather and clear skies since late August provided the ideal opportunity to get to grips with this challenge that has so far eluded me.

At first I used a couple of sessions to overcome some past problems and ensure that everything was stable and worked well for basic tracking and imaging, in particular:

Repair and improve the imaging camera’s AC/DC adapter lead;

Where possible improve all other leads and connections – once bitten …..! In this respect I have significantly re-arranged and tidied up the many power, control and camera leads, which has included the addition of right-angle USB / mini-USB camera connectors that now makes plugging-in easier and produces less strain on the connections i.e. more secure. Simple, cheap and something I should have undertaken long ago;

Revisit EQMOD-ASCOM in order to achieve more robust tracking – especially reviewing the star alignment procedures;

Fit the guide scope using the rings incorporated onto the GT81 OTA, subsequently re-balancing the equipment and improve the mount’s feet positioning.

At this point I spent a couple of nights just playing with the equipment and in particular EQMOD-ASCOM, so as to obtain the best possible alignment; having suffered an enforced absence from imaging I just wanted to have some fun again too. At the end of this process, first using SynScan for polar alignment before switching to EQMOD-ASCOM + Cartes du Ciel for star alignment, I successfully produced a good 10-star alignment model which was then saved for future use. The resulting images already showed some improvement but I still had to tackle PHD. With unusually good weather I decided to leave the final set-up outside under cover, thus preserving the settings for a shot at the aforementioned task of guiding next time. In the interim I then needed to read the operating instructions and watch numerous videos on the use of PHD.

EQMOD-ASCOM 10-point alignment model. With an obstructed view of the northern sky by my house, all points are inevitably located in the southern quadrants.

Like so much of amateur astronomy, I will forever be grateful for the time and effort given by others to help those like me pursue our hobby. The material, videos and responses to my forum queries on guiding have as usual been nothing short of outstanding and very, very helpful. It’s still been difficult to get going but without the help and support of others it would be a complete non-starter. In this respect I’d like to pay credit to SGL and the Open PHD Guiding forums.

Armed with this knowledge I have since undertaken a few sessions using PHD2 with reasonable success, achieving exposure times of 5-minutes and more. Changing conditions and different objects make it necessary to continually finesse guide settings throughout the night and between nights and it’s already obvious that there’s much more to learn. Such adjustments are not always linear or empirical in nature and will often only come from gut feel (experience).

I have chosen to use ASCOM pulse guiding, though my equipment also has ST4-ports which I had initially intended to use due to its apparent simplicity. I am unable to argue the pros and cons of each method but there seems to be an overwhelming preference for pulse. What I do understand (I think) are the greater subtleties that can be obtained with the pulse guiding technique and in particular, the co-ordination it provides with ASCOM, thereby ensuring PHD and the mount communicate with each other to provide essential directional information as well as guiding. I am still investigating the impact of various BRAIN settings but through trial-and-error have progressed since my first guiding session.

First Pass: early guiding results 30th August 2016

Getting better: most recent guiding results 12th September 2016

Calibration of PHD is frustratingly slow and it seems that even after successfully completing the RA-procedure can still fail during the subsequent DEC / backlash clearance. After calibration use of the PHD Guide Assistant can then provide more help in achieving the best settings for the given set-up and conditions, though it is also very slow. However, once completed PHD is fantastic and so far has run well during the night, even when changing objects. Furthermore, I’ve also studied and experimented with the PHD Drift Align tool and am hopeful that by using this I may soon be able to both dispense with SynScan altogether and improve polar alignment, hitherto my imagining nemesis as I cannot see Polaris from my location – a very exciting prospect – what’s not to like?

Starting a sequence of experimentation I chose a familiar but hitherto difficult DSO object to image that should benefit from longer exposures. Having by now reached late-summer / early autumn, there were a few old favourites around such as the Veil and North America nebulae but for these trials I decided to go for the low hanging fruit of M27 or Apple Core nebula AKA Dumbbell nebula.

My previous image of M27 in August 2014!

With limited success I imaged this planetary nebula in my early days of astrophotography but with its 8.0’ x 5.6’ size and apparent magnitude of +7.5, I found it difficult to obtain good detail and colour. However, even without guiding the improved set-up and alignment produced better results at 3-minutes and with +5-minute guided exposures the images immediately showed very noticeable improvement.

The images were taken on four different nights starting on 23rd August and finished on 8th September, during which time the sky was clear and the weather warm with very low humidity, though by the end seeing conditions had started to deteriorate due to the impact of the emerging 1st quarter Moon. All images have been cropped to the same size of 700 x 500 pixels or 2% of the original FOV i.e. an object size of about 0.20%! Given this very small size M27 really is at the limit of the GT81 telescope.

m27-comps-paintfile-cropped

Strictly speaking the images are not fully comparable as the aggregate exposure times are not equal but nonetheless I think the results demonstrate the positive impact of guiding. The final two images are guided but do show greater star distortion, particularly at 8-minutes. I suspect this may be due to the period over which the mount was left outside and would probably have benefited from some alignment tweaking before imaging re-commenced – lesson learned; the severe cropping ratio has also magnified any problems that would probably be less obvious in a larger widefield image. There’s obviously room for improvement but I’m very happy with these early results which I can hopefully now build on.

M27 Apple Core Nebula – my first and favourite guided image | William Optics GT81 + 50mm guide scope & 10-point EQMOD-ASCOM star alignment model | modded Canon 550D + field flattener & Starlight Express Lodestar X2 guide camera | 3 x 300 secs @ ISO 1,600 & full calibration, 3.3% cropped image| 30th August 2016

Unfortunately there is some downside to the longer exposures obtained from Fairvale Observatory: potentially more aircraft tracks and cloud plus more extended imaging time is unavoidable but overall it is, as expected, a major leap forwards for my astrophotography. There’s still much to learn and improve with the technique but for now I am delighted to say that after nearly two years I am at last successfully guiding – would you Adam & Eve it?

Dark Matters

September 7, 2016 by grahamrob in Deep Sky Objects, Equipment, Imaging, Universe and tagged Aquila, Dark Nebula, DSO Imaging, Einstein, Hitchhiker's Guide to the Galaxy, Photography | 2 Comments

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After some months I have just finished reading Walter Isaacson’s outstanding biography of Albert Einstein. I don’t know how the author, as far as I know a scientific layperson and writer of the equally good Steve Jobs biography, is able to pull together Einstein’s thoughts and theories in such an engaging and comprehensible manner that provides both insight and understanding into his scientific thinking, life and personality.

Besides the implications his work already has for nuclear physics and astronomy, even in the 21^st Century we are only just starting to understand and confirm concepts that were either predicted or implied by his work of uniquely pioneering theoretical physics in the early part of the last century – much of which is still difficult even to comprehend, let alone understand. In the world of astronomy two of Einstein’s predictions have only recently been shown to actually exist, with very exciting implications for our understanding of the Cosmos: gravitational lensing and earlier this year, confirmation of the presence of gravitational waves – ripples in the fabric of space-time itself!

Einstein vindicated: In the constellation of Cetus, the galaxy cluster Abell 370 abounds with evidence of gravitational lensing – imaged here in 2009 by the Hubble Space Telescope

During his early work Einstein battled with 19^th Century scientists who continued to believe in the presence of the so-called ‘aether’, as proposed by Isaac Newton in 1718 – an undefined substance that supposedly filled the void in space and was responsible for the transmission of electromagnetic and gravitational forces. Subsequently Einstein’s Special Theory of Relativity was able to explain such effects without the presence of the aether but there remained problems that were finally borne out in 1924 by Edwin Hubble’s evidence that contrary to the prediction of Einstein’s work and previous astronomical theories, the Universe was in fact expanding. However, though serious these observations did not prove to be the end for Einstein’s work, merely the beginning of even more incredible theories that have even greater and more profound implications for the Universe.

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As a geologist by training, my background is scientific and I continue to follow with interest related developments across a broad spectrum. My perception, which I think is justified by facts, is that we are again experiencing something of a quantum change in our understanding of physics at the moment. No ‘new Einstein’ has yet emerged, though Stephen Hawking perhaps comes close and there are many bright minds still struggling to understand what it all means – certainly we seem no closer to a unified theory. At the ‘very small’ scale the increase in particle types since I last studied science in the 1970s is staggering, recently culminating in confirmation of the Higgs boson at the Large Hadron Collider (LHC) in Geneva; almost certainly there’s more to come from the LHC but I’ve already lost track (no pun intended) of what makes up matter.

330px-CMS_Higgs-event

In the meantime, ever since Hubble’s expanding Universe bombshell, the world of physics has struggled to provide an explanation of what’s happening, except to say that for expansion to happen 95% of the Universe must consist of stuff we don’t know about, that is arbitrarily (and misleadingly) called Dark Matter (27%) and Dark Energy (68%), which have theoretical properties of mass and energy that would explain why the Universe is expanding; I find this exciting and even amusing.

Our earliest view of the Universe – the Cosmic Microwave Background, formed some 380,000 years after Big Bang 13.8 billion years ago.

As I get older I look upon the world with increased wonder and ask all the same big questions as everyone else. I still find science itself exciting as we continue to unlock nature’s wonders but have increasingly had a suspicion that despite the incredible discoveries made by mankind, we are really only scratching the surface of what’s going on. The prospect that there is still so much we do not know also provides many possibilities for what is really happening; a consoling thought as I move towards old age! I believe it’s humbling for science that they (we) only know what 5% of what the Universe is made of. Notwithstanding, like Deep Thought’s answer to the question “what’s the meaning of life the Universe and everything?” in Hitchhiker’s Guide to the Galaxy (answer = 42), it will keep thousands of scientists, their computers and the media gainfully employed for many years to come. In the meantime, perhaps I can already help them?

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Early on in my astroimaging odyssey I discovered an interest in Deep Sky Objects, in particular nebulae. I find their very nature beautiful, as the birthplace of new stars and matter itself their science is also fascinating – as Moby puts it We Are All Made of Stars. There are numerous types of nebulae of equally diverse origin, with a complex variety of delicate forms that can be both enthralling and beguiling. Generally they are made of gases and dust that emit types of light that often cannot be properly seen with the naked eye and only captured by photographic methods using various sophisticated imaging techniques, such as modified cameras or narrow band filters; their very elusiveness is part of the attraction. I have been fortunate to photograph a number of these features and never get tired of their science and beauty. However, there are other types of nebulae that are quite different.

Whereas the ‘common’ nebula is fundamentally based on activity that results in the emission or reflection of light, their other ‘ relations’ are the result of a quite opposite process. In this case so-called dark or absorption nebulae are clouds of dense interstellar dust that obscures or scatters light from nearby objects behind, such as stars or emission and reflection nebulae, resulting in large, unusually dark patches in the sky. I’ve imaged a few of these features before, where in the case of Orion such a process has produced Barnard 33, better known as the Horsehead Nebula – a dark interstellar dust region in the shape of yes, a horse’s head. Recently I set out to image another less famous but equally exciting dark nebula.

Other than resorting to solar astronomy, the period of summer sometimes seems like something of a barren period, further compounded by short nights and the absence of astronomical darkness. Notwithstanding, look closely and there’s plenty happening and, if you’re lucky, it’s possible to work into the night enjoying the warmth of the season too; I’ve recently been able to stay out in a shorts and T-shirt until past 3.00 a.m. – compare that to January – apart from the comfort there’s also no sign of the astronomer’s enemy, dew. This year my wife has grown and strategically placed two night flowering plants close to my equipment, which on warm evenings produce pleasant aromas that waft across Fairvale Observatory whilst I’m working. What’s not to like?

Night Phlox (Zaluzianskya Capensis). Though quite this small plant produces a strong smell of violets at night.

Nicotiana Alata. This large plant produces a strong, fragrant smell.

Whilst there’s no Orion (though it has made an appearance in the east from at about 3.00 a.m. since late August) or Taurus (also rising shortly before Orion) with all their iconic features, instead the summer arm of the Milky Way passes across the sky from about 8.00 p.m. presenting numerous opportunities of its own in the early part of the night.

Aquila b142

This time my targets were Barnard 142 & 143, located just west of the star Tarazed in the Aquila Constellation. Roughly equivalent to the full Moon in size distance and some 2,000 light years away, both are dark nebulae which viewed together against the dense background of stars in the Milky Way clearly make the shape of the letter E – shown first below in inverted colour.

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Previously I’ve been too busy looking for the more conventional DSOs but at some 30 arc minutes, the E Nebula – as it is known – is another excellent imaging target for the William Optics GT81 field-of-view.

E Nebula, AKA Barnard 142-3 in the Aquila Constellation. William Optics GT81 FD & modded Canon 550D + 0.80x Field Flattener | 15 x 180 sec @ ISO 1,600 | 26th August 2016

E Nebula, Barnard 142-3 Dark nebulae

It turns out there are many such dark nebulae, so I hope to be imaging others in the future. I wonder what Einstein would have made of these and moreover, the hypothesis of Dark Matter & Energy? It seems that once again he may have foreseen such developments and their possible existence may ironically even be found to relate to the cosmological constant used in his original General Theory of Relativity.