February | 2018 | WATCH THIS SPACE(MAN)

RGB HaOO XXX2

It’s nearly 4-years since I started astronomy, like so many inspired after observing Saturn through a telescope. Not just any telescope but the 13” Astrographic Refractor at the Observatory Science Centre in Herstmonceaux. Built in 1890 specifically to make use of the then new technique of astrophotography, the telescope was first employed as part of the worldwide Carte Du Ciel project to map the entire night sky by photography and subsequently for a crucial test of Einstein’s then new theory of General Relativity. Soon thereafter I was to view the aforesaid planet once again with my first, newly purchased Skywatcher 150PL Newtonian telescope. Inevitably something of a lesser view than that at Herstmonceaux it was nonetheless just as exciting, if not more so. I was hooked!

I then attempted afocal imaging using a compact camera held up to the telescope eyepiece but with poor results, except in one respect. By clamping the camera onto the front of the eyepiece and achieving longer exposures, nebulosity otherwise unseen with the naked eye was revealed in the resulting image, in this case Orion’s Nebula. As crude as the image was, for me the penny had dropped and I’ve been pursuing images of the hidden beauty of the night sky ever since.

rosette map

ngc2237map

Like mariners, through astronomy I have by now become accustomed to the seasonal procession of the night sky wonders throughout the year, none more so than the Rosette Nebula. About 100 light-years across and 5,000 light-years from Earth, the Rosette Nebula is surely one of the annual highlights for most astrophotographers? Located just east of Orion, the Rosette is at its best between December and February, so that I was first able to image this beautiful object myself at the end of 2014.

As a very large HII region the Rosette Nebula emits light mainly at narrowband wavelengths, which produces wonderful but mainly red colours when imaged with a modded DSLR camera. As my astrophotography and equipment have since developed, it has become a pleasure and challenge to image objects as they return each year such as the Rosette, thereby also charting my own improvements or otherwise from year-to-year. Its size makes the Rosette an especially attractive target for smaller telescopes such my own with an 81mm aperture, which nicely fills much of the sensor of an APS-C camera.

Despite having purchased a new ZWO1600MM-Cool mono camera at the end of 2016, by the time I was ready to use it at the end of the following March, the Rosette Nebula had almost disappeared over the western horizon for another year. Notwithstanding, in the limited time remaining I managed to capture a few Ha-OIII-SII subs, thus marking first light for the camera, which ironically resulted in one of my favourite images for 2017. Using narrowband for the first time it was immediately possible to see the potential of the new camera when imaging this type of object.

Returning from an extended overseas trip at the end of January this year, 10-months had passed since my last encounter with the Rosette Nebula last March and I found myself with the first real opportunity to image the nebula properly with the ZWO1600MM-Cool camera. Since last year I’d acquired more knowledge and experience with the camera, plus this time the Rosette was now in the south eastern quadrant and provided significantly more imaging time than before.

After a break of nearly two months I needed to sort out the equipment, refocus the camera and start a new alignment model in EQASCOM. For the first time I also decided to use longer exposure times of 300 seconds, which altogether produced a good Ha+OIII Bi-Colour image (top of page – awarded BAA Picture of the Week 4th March 2018); whilst much longer exposures are used with conventional CCD sensors, such is the sensitivity of the CMOS mono sensor in the ZWO camera that 5-minute exposures provide exceptionally good quality data. Overall the impact of longer exposure, good focus, tracking and much longer total integration time had a noticeably positive impact on noise and overall image quality, though there’s still room for improvement – there always is!

To some extent, even after a year I’m still in the experimental phase with this camera. For most of 2017 I used a high gain setting of 300 but this time I chose the Unity gain setting of 139 and for interest also imaged at a shorter exposure of 180 seconds. Comparison between the two settings for Ha images – Unity gain at 300 and 180 seconds – shows that for such a nebulous type of feature as the Rosette, Unity gain works very well at the longer 300 second exposure (first image below) but not 180 seconds (second image below), which is too short to collect sufficient data.

Picture saved with settings embedded.

Notwithstanding, in the past I have found shorter exposures at Unity or less have generally been more suitable for brighter objects such as star clusters or galaxies like Andromeda. An alternative SHO Hubble Palette image below of the Rosette Nebula at Unity gain and 300 second exposure also compares more favourably with the same image taken last year using less subs, higher gain and shorter exposure time.

Untitled-2 Crop2 (Large) When the object is right, such as the Rosette Nebula, narrowband imaging using the ZWO camera produces exceptional results. This is evident in these recent images where it’s now possible to clearly see structural elements of the nebula, as well as the star fields located within. Frankly I am very excited by these new images and can’t wait for next year to come around again!

Postscript: Research at Leeds University just published suggests that the Rosette Nebula is a disc but I believe my eyes and this image and many others which says otherwise!

	IMAGING DETAILS
Object	Rosette Nebula NGC 2244 + 2237, 2238, 2239 & 2246
Constellation	Monoceros
Distance	5,000 light-years
Size	Approx. 100 light-years or 1.3^o
Apparent Magnitude	+9.0

Scope	William Optics GT81 + Focal Reducer FL 382mm f4.72
Mount	SW AZ-EQ6 GT + EQASCOM computer control
Guiding	William Optics 50mm guide scope
	+ Starlight Xpress Lodestar X2 guide camera & PHD2 control
Camera	ZWO1600MM-Cool (mono) CMOS sensor
	FOV 2.65^o x 2.0^o 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, Deep Sky Stacker & Photoshop CS2
Exposures	12 x 300 sec Ha, 6 x 300 sec OIII & SII (Total time: 120 minutes)
	@ 139 Gain 21 Offset @ -20^oC
Calibration	5 x 300 sec Darks 20 x 1/4000 sec Bias 10 x Flats Ha, OIII & SII @ ADU 25,000
Location & Darkness	Fairvale Observatory – Redhill – Surrey – UK Typically Bortle 5
Date & Time	9^th February 2018 @ 22.00h

IMG_9050 (Large)

I’ve recently returned from visiting family on an extended trip to Aotearoa – Maori for New Zealand – and whilst travelling around used the opportunity to learn something about astronomy in that part of the world (NZ Astro Directory). Of course, the main difference Down Under is that it’s currently summer, plus everything in the night sky is upside down.

Topsy Turvy – everything’s in the wrong place ! Red arrow = Betelgeuse, Yellow arrow = Orion Nebula

It’s obvious really but relatively speaking the sky has not changed, you’re just personally inverted compared to the Northern Hemisphere – which from the point of view of astronomy takes some getting used to when looking at otherwise familiar objects such as the Moon or Orion Constellation. Although being their summer, at our principal location of latitude of 38^o on North Island there was more than four hours of astronomical darkness even on the December solstice; viewed from the perspective of the Northern hemisphere, it is interesting to note that this is about the same latitude as Athens or the Korean DMZ!

Half Moon at home- Surrey, UK

Moon in NZ: upside-down & crescent reversed

It’s all about perspective – obvious really!

Although the weather was mostly very good, I was struck by how frequently the sky at night was cloudy – just like good old Blighty – it is after all also known as The Land of the Long White Cloud by the Maori. Notwithstanding, as a country with only 4.85 million people most of the country is rural or even desolate, so that when the skies are clear the darkness and seeing conditions can be quite spectacular. Viewing conditions are particularly good on South Island around the Lake Tekapo and Mt Cook district where a number of astronomy ventures are based, including the University of Canterbury’s Mt John Observatory – shown at the beginning of this blog. For practical reasons I was restricted to taking only limited equipment – DSLR & lenses + Gorilla Pod & ball head + Vixen Polarie tracker + 10×50 binoculars – but was still able to obtain some pleasing images during the trip.

Mt Cook from near our campsite – the night sky here was fantastic

Early on it became evident that New Zealand seems to have all the right conditions required for the formation of lenticular clouds (altocumulus lenticularis). I’m presuming this is related to its somewhat exposed position between the South Pacific Ocean and Tasman Sea, thus providing favourable wind and moisture conditions which are then influenced by the mountainous tectonic terrain that runs along the spine of South Island and the volcanic topography of North Island. Whatever it is it works, providing really beautiful and often spectacular sights of these elusive and somewhat rare high altitude cloud phenomena.

IMG_9097 (Large)

Lenticular clouds south of Mt Cook – South Island

IMG_9457 (Large)

Lenticular clouds near Te Awamutu – North Island

Prior to arriving in New Zealand I tried unsuccessfully to link up with some local astronomy clubs. However, close to our base near Te Awamutu on North Island I was able to visit the Te Awamutu Space Centre at nearby Kihikihi.

The Te Awamutu Space Centre – Kihikihi

Conceived and run by the enthusiastic Brit Dave Owen (well he wasn’t going to be a Kiwi was he?), the Centre is an eclectic and interesting collection of space, space programme, astronomy and related educational items (see below).

Essentially the Centre is an outreach programme, which would be of interest to anyone in general, young and old, as well as the seasoned astronomer. I particularly found the area on New Zealand astronomy & astronomers, astronauts and the historical role of Maoris in astronomy very interesting.

Maori star names of Mataraki (Pleiades)

As we travelled the length and breadth of the country with the tantalising promise of some very dark skies, I was keen to view and image the Milky Way and particularly the Large and Small Magellanic Clouds, which are only visible from the Southern Hemisphere. Thwarted for a while by cloud cover I eventually got my first look at all these features whilst camping near the base of the 3,724 metre Mt Cook on South Island. The sight did not disappoint but I was unfortunately unable to obtain any images on this occasion.

No worries (as they say in New Zealand – frequently!), a few nights later whilst camping at the improbably named Slab Hut Creek (site of old alluvial gold workings) west of the historic mining town of Reefton, I was at last able to image all these features. Remotely situated in the middle of woods adjacent to the aforesaid gold creek, the night sky was inky black, albeit with some passing cloud from time-to-time. Furthermore, located in the centre of the opening were two very large quartz boulders, which provided an ideal platform on which to set up the camera and Gorilla Pod.

A few tons of conveniently placed quartz helped imaging later in the night!

I didn’t get much sleep that night but it was a magical experience and I was thrilled to image both the Milky Way and Magellanic Clouds not individually but together. As an added bonus we were also able to successfully undertake some gold panning during the day in the creek!

IMG_9244 (Large)

The Milky Way at Slab Hut Creek with the Large & Small Magellanic Clouds

Thereafter I was hindered for the next few weeks by Christmas events and the inevitable full moon at the start of January, though the ISS did pass directly overhead on one evening (New Zealand from the ISS). However, 10-days later back on North Island at our cottage in the Waipa district, I was eventually able to view and image once again the wonderful sight of the Milky Way + Magellanic Clouds + Southern Cross at the same time – sky chart and image below.

Ohaupo Sky

IMG_9984 (Large)

From our base on North Island: The Milky Way & Magellanic Clouds (right) + Southern Cross just above the left-hand side of the roof line

When the conditions are right the night sky in New Zealand is truly outstanding. I would have liked to spend time there with the full astronomy set-up and camera that I use in the UK but for now I was very pleased to experience and enjoy Antipodean astronomy, it really is worth the long journey.