Comet 46P/Wirtanen

Comet 46P/Wirtanen

Object: 46P/Wirtanen

Type: Comet
Constellation: Taurus
Distance: 0.0806 AU (7.5 million km)

Date: December 12th. 2018
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 30 x 120s luminance, 20 x 30s each for RGB (for comet, same again for stars).  Additional 60s (30 taken) and 30s luminance frames (70 taken) were also obtained (see below) in this session.

Comet 46P/Wirtanen was discovered by Carl A. Wirtanen in 1948 at the Lick Observatory, California on a photographic plate.  The plate was exposed on 17 January 1948 during a stellar proper motion survey at the observatory.  It took over a year before the object was recognised as a short-period comet due to a lack of observations.

Comet 46P/Wirtanen has an orbital period of approximately 5.4 years and belongs to the “Jupiter Family” of comets. Jupiter-family comets will occasionally have their orbits perturbed when they make a close approach to Jupiter because its strong gravitational field can alter (sometimes quite significantly) a comet's path through space.

In the case of 46P/Wirtanen, it underwent two such interactions with Jupiter (in April 1972 and February 1984) that pushed its orbit about 50 million miles closer to the sun as well as very near to the orbit of Earth.

Perihelion passage of comet Wirtanen will be on 16 December 2018 when it will pass 0.078 AU (7,220,000 miles) from Earth.  Close though this encounter is, the comet is relatively small in size with an estimated nuclear diameter of just 1.2 kilometers (unlike the Great Comet of 1997, Hale-Bopp, with its 60 km nucleus) and so will not appear to be particularly bright.  

46P is expected to reach magnitude 3, but this light is spread out a bit across the comet’s visual area which, unlike a star, is not a point source. It is therefore right at the limit of naked eye visibility. I could not see it without binoculars, even though I knew exactly where to look. This is the brightest prediction of known and future passes of this comet. This is also currently the brightest prediction for all comet passes in 2018, although even by the usual UK tabloid’s moronic standards, it can hardly be described as a “head-scorcher”….

Sensible information about 46P Wirtanen can be found here.

The "seeing" on the evening of December 12th. was horrendous.  Focussing was a challenge as star shapes fluctuated wildly between focus frames. I initially gathered 70 x 30 second luminance frames and 20 x 30 second frames in RGB, (plus a further 20 x 30 second RGB frames for star colour once the comet had drifted out of the field of view). No evidence of a tail could be seen. Setting PHD to guide on the comet nucleus seemed to work fairly well, although the longer subs at 60 seconds and 120s seem to be plagued with noise and gradients - I think some high cloud had set in.  This made processing a bit difficult and it took a few iterations to get the noise reduction and background brightness into a presentable image.  The 120s subs did show a hint of a tail and the final result is shown above.  The shorter sub stacks did not show much in the way of cometary detail but are shown below.

A map of the comet's perihelion passage through the constellation of Taurus is shown below:

Track of 46P through Taurus, 11-16 December (position marked every 12h)

Using the sigma stacking function in Astroart, and "one star" alignment gave an image of the comet with star trails virtually eliminated.  The LRGB stack showed the bright green colouration of the comet itself.  I layered the RGB star stack over it to give coloured stars in the final images.

46P - Larson Sekanina filtered image

The striking green fuzzball (see an explanation of the colour here) rather dominates the image and it was a bit tricky to stop it being spoiled by an "onion ring" brightness gradient, which I still haven't completely eliminated.  The core does show a tiny bit of detail and a hint of a tail.

The AstroArt image processing programme offers something called a Larson-Sekanina filter, which uses a lot of complex math to allegedly pull out cometary detail from raw comet images. Applying this to the luminance data stack gives a result (left) does seem to show a tail and other additional details that correspond to faint features in the colour image above.


Below is a GIF animation using the 70 x 30 second luminance frames from above, showing the comet moving against the sky background.

This 3 second sequence shows the movement of the comet between 19.07 and 20.01 on December 12th, 2018, over a span of about 9 arc-minutes (or about a third of a full moon diameter).  The comet appears to graze the 9.7 magnitude Hipparcos catalogue star HIP 16342.

Comet 46P Wirtanen - (stack of 30s subframes)

Comet 46P Wirtanen - (stack of 60s exposures)

IC 1396A (vdB 142) & IC1396B - The Elephant's Trunk...

IC 1396A (vdB 142, left) and IC 1396B (centre); The "Elephant's Trunk"...

Object: IC1396A (vdB 142) + IC1396B

Type: Reflection/emission/dark nebula
Constellation: Cepheus
Distance: 2400 light years

Date: November 18th. and December 7th. 2018
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 24 x 600s H-alpha, 20 x 600s OIII, 20 x 150s blue (2x2 binned), 30 flats/dark flats per channel, hot pixel removal in Astroart (no main frame darks).

Popularly called the Elephant's Trunk Nebula, IC1396A and IC1396B are parts of a much-larger region of faint nebulosity (IC 1396) that lies 2,450 light-years away in the constellation of Cepheus and which spans an area of over 5 degrees as seen in the sky.

Location of IC 1396A in the sky...

IC 1396A is a bright-rimmed cloud (BRC) on the periphery of the associated giant H II region IC 1396 produced by the Trumpler 37 star cluster. Over 250 young stars in and around IC 1396A have been identified, with a spatio-temporal gradient of stars from the IC 1396A cloud towards the primary ionizing star HD 206267 being found.

The entire IC 1396 H II region (Sh 2-131) is excited mainly by the star HD 206267 located at the centre of the region (and just out of shot to the left in the above image) in the 4 million year-old cluster Trumpler 37. IC 1396 has a rich population of >20 bright-rimmed and cometary globules seen in silhouette against the emission nebula.

Many of the clouds reside on the large molecular shell surrounding the H II region, and sites of possible star formation have been identified in/around at least several globules, including sites of substantial star formation in IC 1396A. 

Lying 15′ west of HD 206267, IC 1396A is the BRC closest in the sky to HD 206267.  Its optical rim is the brightest of all rims and the cloud is thus likely to be the physically closest to HD 206267. IC1396B lies slightly to the west of its brighter sister.

A cavity in the molecular cloud is present in the head of the A globule and contains a pair of young stars (LkHa 349 and LkHa 349c) that formed from the dense gas in the globule, and which have cleared the spherical opening within the head of the globule. They provide the glint in the eye of the elephant, as seen in a crop of the above image (below).

These stars can be seen in both optical and Spitzer infrared images. While one of these stars is much fainter than the other in optical images, they show a similar brightness in the infrared Spitzer image. This indicates the presence of a thick and dusty disk around LkHa 349c. These disks, called circumstellar disks, are the places where planets and moons will likely form in the future. They are much thicker in the early stages of star formation and glow brightly in infrared. 

IC1346A is also designated as vdB 142. The vdB (van den Burgh) catalogue was originally published in 1966 by Sidney van den Bergh, and referenced 158 reflection nebulae:A study of reflection nebulae, van den Bergh, S., 1966.  Later it was expanded to 159 objects by René Racine:Stars in reflection nebulae, Racine, 1968. The catalogue contains information for all stars with a spectral classification of BD and CD lying north of -33 deg and which are surrounded by reflection nebulosity visible on both the blue and red prints of the Palomar Sky Survey.  The nearer reflection nebulae lie predominantly along Gould's Belt, whereas the more distant ones are concentrated in the galactic plane.

Gould's Belt itself was first described by Benjamin Gould in 1879 as a collection of bright and massive stars that form a ring in a projection on the sky.  This rings traces out several molecular clouds in the local part of the galaxy where star formation is prominent.  Gould's Belt is estimated to have a diameter of 3000 light years.

The hydrogen alpha image (below) shows a detailed mixture of bright and dark nebulosity.

IC1396A/B in hydrogen alpha..

The OIII and blue channel data show very little data by comparison.  The Ha, OIII and blue channels were RGB combined in AstroArt (Ha = red, OIII = green, blue=blue).  The RGB image was then exported to PaintShop Pro and curve adjusted, with the Ha channel then added back as a luminance overlay. Blue haloes on the brighter stars were manually removed with the colour replacer tool, with final contrast and curves adjustment to give the final image shown at the top of this post.

I also tried a HOO version, using the H-alpha data as the red channel, and the OIII data for green and blue...

IC 1396A/B as HOO

This rendition has the fashionable orientation of north to the right and is fashionably darker. My preference is to try and present deep-sky images in their correct aspect, but in this case the columnal nature of the dust clouds is nicely emphasised.  I always think that in this view, the nebula resembles a woman walking away from the field of view...

The Cave Nebula (Sharpless 2-155)

The Cave Nebula (Sh2-155)

Object: Sharpless 2-155 (Caldwell 9)

Type: Emission nebula
Constellation: Cepheus
Distance: 2400 light years

Date: November 2nd. 2018 (Ha), 17th (RGB)
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 40 x 250s H-alpha (2x2 binned), 20 flats, hot pixel removal in Astroart (no darks). 10 x 250s (2x2 binned) each for RGB

The Cave Nebula is part of an extensive region of ionised hydrogen gas associated with the Cepheus B giant molecular cloud.  The ionisation is caused by radiation from a group of young, hot stars hidden within the dust cloud, which knocks hydrogen electrons into "excited" states that re-emit radiation and cause the surrounding low-pressure hydrogen gas to glow.  Sh2-155 is just a small part of an extensive area of nebulosity in the Cepheus/Cassiopeia region that includes several notable emission nebulae.  It lies about 3.5 degrees south of iota Cephei...

The evening of November 2nd. was clear but the atmosphere was very unsteady. I decided to run the Atik camera in 2 x 2 "binned" mode, partly to make autoguiding accuracy less critical and also because the Cave Nebula is extremely faint and I didn't fancy spending hours getting enough 20 or 30 minute subs to beat down the background noise.

However, this loses a bit of resolution, but the poor seeing would have done that anyway. The seeing did make focussing a bit hit and miss however, and I should really have looked at the first couple of subs a bit more closely.  When I finished the session and downloaded the images next day, I was frustrated to find that the stars were out of focus, with some showing a "doughnut appearance".  At this point I would normally delete them and wait for another imaging opportunity, but clear, moon-free nights at reasonably civilised hours are an extremely rare occurence in my part of the world, so I decided to see if the situation was redeemable.

The Cave Nebula in H-alpha

Fortunately, a couple of software routines in Astroart (Digital Development followed by a few iterations of Lucy-Richardson deconvolution using a mild Gaussian point spread function, for the record) were able to pull the star and nebulosity details back into a reasonably decent shape.  A bit brightness and contrast adjustment (using "curves") and noise removal (mild edge-preserving smooth), both in PaintShop Pro, gave the Hydrogen alpha image above.

I did try and get some hydrogen beta data, but 300 second exposures at 2x2 binning revealed not a jot of nebulosity in the area, so I guess this object just doesn't emit in this part of the spectrum.

It was a couple of weeks before I was able to get some RGB data to make up a colour image.  250 second subs (2x2 binned) through Baader red, green and blue filters were stacked, aligned and RGB combined in Astroart to give this rather disappointing RGB image...

RGB - Cave Nebula area

Whilst the star colours were fine, there was hardly any trace of nebulosity visible. I guess a 60% waxing moon and shortish subs washed out the contrast.  Clearly, I would not be able to directly use the H-alpha frame as a luminance layer, as the lack of any nebula colour in RGB would just result in coloured stars on a grey nebula.

I decided to colourise the existing H-alpha frame by pasting it on to a red background in "Hard Light" mode in PSP.  This gave a bright red nebula image with white stars...

The brighter H-alpha regions tend to remain washed out and so I prepared a second mask as above, but combining in "multiply" mode. This gave a completely red nebula with red stars...

"Colourised" H-alpha frame...

Selecting the bright area (with a feather of about 20 pixels), I pasted and aligned the area over the "Hard Light" image.  With careful use of the eraser tool in PSP and a partial blending (around 50%) it was possible to greatly reduce the remaining washed-out H-alpha regions...











Pasting this over the RGB stars in "lighten" mode at around a 70% blend gave a reasonable mix of star and nebula colour,  A few tweaks to the final colour and contrast using curves gave the final result you can see at the top of this post.

OK, never a NASA APOD, but given the poor quality of data I don't think it turned out too bad.

The Crescent Nebula - NGC 6888

The Crescent Nebula: NGC6888

Object: NGC 6888

Type: Emission nebula
Constellation: Cygnus
Distance: 5000 light years

Date: September 3rd. and October 9th. 2018
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 20 x 300s H-alpha, 16 x 450s OIII, 20 flats for each channel, hot pixel removal in Astroart (no darks).

NGC 6888, the “Crescent Nebula”, is a cosmic bubble of rarefied gas about 25 light-years across, formed by stellar winds from its central Wolf-Rayet star (WR 136).  Wolf–Rayet stars are massive stars that have completely lost their outer hydrogen shell and are fusing helium or heavier elements in its core. This star is shedding its outer material in a strong stellar wind, ejecting the equivalent of the Sun's mass every 10,000 years.  The nebula's complex structures are the result of this strong wind interacting with material ejected in an earlier out-gassing phase.  Burning its helium fuel at a prodigious rate and nearing the end of its stellar life, this star will ultimately end in a supernova.

The above image uses narrowband image data obtained by passing the light collected by the telescope through interference filters that isolate light from hydrogen and oxygen atoms in the nebula.  The "forbidden" ionised oxygen atoms produce the blue-green hue enshrouding the detailed folds and filaments of the main nebula.

NGC 6888 is located near Sadr, the central star in the Northern Cross of Cygnus, within the "Summer Triangle" of the bright stars Deneb, Vega and Altair.  The whole area is suffused with wisps of emission nebulae, that show up well in monochrome H-alpha images (below)

Wide field - H-alpha only

A crop of the area shows up the filamentary structure of the nebula...

Crop

These images are the first I have obtained from my new Atik 460EX CCD camera.

Needless to say, any investment in shiny new toys results in conditions that prevent you from playing with them.  Nearly a month elapsed between the collection of the H-alpha data and the OIII frames, due to a combination of moonlight, high haze and horrendous local dew and mist problems.  The night I finally managed to collect the OIII frames was cut short as the humid conditions led to veritable waterfalls of dew running down the outside of the 'scope and the insides of the observatory walls, to the extent that I was worried about shorting out the electrics!

Processing consisted of sigma stacking in AstroArt (which eliminated the aircraft light trails in several of the subs - another challenge associated with imaging from the Medway valley region, which often lies under the Heathrow/Gatwick/London City airport flight paths), with hot pixel removal set at 70%, followed by noise removal and curve adjustment in Paintshop Pro.  The Ha and OIII stacks were taken back into Astroart for registration, and a false green channel then generated in PSP by layering the two narrowband stacks and "multiplying".  The three channels were then RGB combined in Astroart, with a bit of tweaking in PSP to give the final colour image above.

I still feel that the final colour image is a bit flat, and would benefit from some RGB data to give some colour to the field stars.

It's still an improvement upon my first attempt at imaging this nebula, from some 13 years ago...

Lightning over my observatory...

A single frame grabbed with PaintShop Pro Animation Shop from a 30 second video shot with my old Sony Cybershot...

Lightning, 07 August 2018

Mars and Saturn...

Mars has just passed opposition but is low down in the constellation Capricorn, rising to no more than about 12 degrees above my southern horizon. As a result of this, the combination of unsteady, hot summer air and atmospheric refraction makes conditions rather difficult for planetary imaging. Added to that, surface features on Mars have recently been obscured by a planet-wide dust storm, which is only just subsiding.

Nevertheless, I thought it might be worth trying to record a closer view of the baleful, dull red coal that is currently rising in my south-eastern sky at around 21.00.  Other than the moon, Mars is, at the moment, the brightest object in the night sky, with an unmistakable fiery hue that fully justifies its name of "the Red Planet".  Its magnitude is -2.7, but this will fade over the next few months as the planetary orbits open up the distance between us.

Mars, August 2nd. @ 23.15

This was taken using an old Phillips TouCam and a x2 barlow lens fitted to a Celestron C9.25.  The planet is too low down to be seen from my observatory so I set the scope up on my balcony, which offers unrestricted views to the east and south.  A one minute AVI file was taken at 25 fps and the output processed in Registax.

The southern polar ice-cap is just discernible as a lighter smudge at the bottom of the disc but other than that, surface details are just blurry blobs.

Similarly, I thought I'd have a go at Saturn, which passed opposition in June and is also low down in southern sky in the constellation of Sagittarius,  Although at a slightly greater elevation than Mars, (16 degrees at best at the moment), seeing conditions are just as poor.

Saturn, August 2nd. 22.45.

Set-up and exposures were as for the Mars shot above. Some planetary banding and the Cassini division in the rings are clearly visible, although again the image is blurred.

Messier 51 - The Whirlpool Galaxy...

M51- The Whirlpool Galaxy

Object: M51 (NGC 5194/5)

Type: Spiral Galaxy
Constellation: Canes Venatici
Distance: 23,000,000 light years

Date: 6th & 7th May 2018
Equipment: SXV-H9, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 50 x 200s luminance, 10 x 100s each for H-alpha, G&B (2 x 2 binned), 20 flats for each channel.

Lurking high in the early summer sky just under the tip of the tail of the Great Bear, the twin cores of Messier 51 show up as two softly glowing points of light in my 8-inch VC200L.  It takes the miracle of a CCD to allow backyard astronomers to visualise the spiral structure and wispy star trails associated with this pair of interacting galaxies.  Or a large-aperture telescope...

I used H-alpha as the red channel to highlight the star-forming regions along the galaxy's spiral lanes. I have to manually refocus upon changing filters (particularly when switching from H-alpha to the RGBs) and the beefy but rather crude rack and pinion focuser on the Vixen ED114 does give rise to a fair bit of image shift. On this occasion for some reason, Astroart's co-register function subsequently struggled to line the H-alpha channel up accurately with the luminance/green/blue ones, hence some funny haloes around the stars.

But after four consecutive clear nights, sleep deprivation is starting to set in and so this one will do for now...

More about this object here...

Messier 5 - Globular cluster in Serpens...

Object: M5 (NGC 5904)

Type: Globular cluster
Constellation: Serpens
Distance: 2450 light years

Date: 4th & 5th May 2018
Equipment: SXV-H9, Vixen 114mm f5.3 ED refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 50 x 30s, 30 x 100s and 20 x 300s luminance, 25 x 100s each for RGB (2 x 2 binned), 20 flats for each channel.

At a magnitude of 6.4, M5 can readily be glimpsed through binoculars as a "fuzzy star", midway between fourth magnitude stars Epsilon Serpentis and 109 Virginis.

M5 often seems to be overlooked in favour of its flashier cousin, the "Great Globular Cluster" M13 in nearby Hercules, yet it is only half a magnitude fainter and in many ways is a more rewarding object to view through a telescope.  In my 8-inch Vixen VC200L , M5 shows up as a cluster of pin sharp stars, gradually brightening, yet still resolvable, right the way to its bright core.  M13, although bigger and brighter, doesn't offer as "granular" an appearance, at least not to me.

For imaging, the challenge is to capture M5's outlying stars, without having a "burning out" look to its bright core.  Luminance stacks of three different exposure lengths were layered and blended in PaintShop, to give a final luminance frame showing an apparent resolved core of stars.  This was combined with an RGB stack in AstroArt to give the final image.

Skies were very clear for the two nights needed to acquire the frames I wanted, but the seeing seemed a little variable, giving rise to a PHD guiding graph that often resembled an ECG trace.  Still, PHD worked its magic and the stars still came out OK-ish, with only a trace of distortion towards the outermost corners of the final image.  Clear skies also helped keep the background noise down, without having to resort to clipping or smoothing.

And it was so nice be able to sit out at night in the observatory at a balmy 10 degrees...

More info on this galactic shepherd can be found here...

M104 - The Sombrero Galaxy...

Object: M104 (NGC 4594)

Type: Elliptical galaxy
Constellation: Virgo
Distance: 31,000,000 light years

Date: 18th & 19th April 2018
Equipment: SXV-H9, Vixen 114mm f5.3 ED refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 70 x 200s luminance, 5 x 200s each for RGB 2 x 2 binned), 20 darks and bias frames, 20 flats for each channel (image stacking, hot pixel and gradient removal in Astroart, curves and colour composition in Paint Shop Pro).

I had never attempted to image this galaxy before, and thought it might be a bit of a challenge given its low location in the southern sky, which for me is also blighted by light pollution from the Aurora Maidstonealis.  M104 is quite a small object (in visual terms, of course!) for a relatively small aperture but I was curious to see how it would turn out.

In terms of imaging, I find that light pollution filters don't really offer any contrast boosting effect, and that image processing seems to be a better option to offset light sky backgrounds.

Given that these were the first clear nights in nearly six weeks I couldn't really ignore the opportunity even though the seeing wasn't great and the sky not truly dark (high haze, I think). On the plus side, the moon was new and caused no glare problems.  Nevertheless, the conditions led to somewhat noisy sub-frames with gradients that I scrubbed up as best I could using the nifty Astroart gradient removal plug-in, plus noise flattening in PaintShop Pro (curves and edge preserving smooth).  I don't normally bother with dark frames but it did seem to help with the background noise in this case.  My ancient SXV-H9 camera is not set-point cooling regulated and so maybe the warmer weather is adding a dose of electronic noise to my subs.

The output is never going to win any prizes of course, but in the end I was sort of OK with this effort, even if it only shows the dust lane and little else.

Good old Wikipedia tells us more about this object here...

NGC 2264 - The Christmas Tree Cluster & Cone Nebula...

Object: NGC 2264
Type: Open Cluster & Emission Nebulae
Constellation: Monoceros
Distance: 2400 light years

Date: 31 January, 06 & 10 February 2018
Equipment: SXV-H9, Vixen 114mm f5.3 ED refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 70 x 300s H-alpha, 20 x 300s RGB, no darks (hot pixel removal in Astroart instead).

Subframes were stacked in Astroart, the outputs converted to TIF files and then colour-composited in PaintShop Pro. I gathered the colour data on the third night, but I quite liked the mono H-alpha image on its own, so I posted that as well (below).

The colour data was a bit of a pig to process with the software I have.  First of all it became apparent that 300 second subs in H-alpha probably weren't long enough.  I had to stretch the resultant stack quite a way to get any decent detail, which introduced more noise than I really wanted. Then the blue colour stack turned out to be a slightly different size to the others, despite all being full frame without any need to resize.  I always refocus between filter changes as the colour correction on my old Vixen 114 ED refractor is not brilliant, so I guess this was the cause, particularly on the blue channel.  This made it difficult to stack the images for colour composition.  I did my best to manually rotate and resize in PaintShop, but the stars still show some odd haloes where the channels didn't line up.

I made two colour images, one created by the addition of green and blue channels to the H-alpha image above, which was used as the red channel for an RGB composite. This was a rather violent red, as anticipated, so I blended it with an HaRGB stack, which was the usual washed-out pink.  The blend gave a nice colour balance. The blue brilliance of the brighter stars in the cluster has led to some flaring around them.  I find the effect quite pleasing, however.

Clicking on either image pulls up the image icons, which can each be clicked on to "blink" each image. 

The Christmas Tree Cluster is a relatively young open cluster, formed between 3 and 30 million years ago. It is part of the NGC 2264 region, along with the Cone Nebula and the Fox Fur Nebula (Sharpless 273), and belongs to the Monoceros OB1 association, a loose association of very young stars located in the Orion Arm of the Milky Way.

The Christmas Tree Cluster (discovered by William Herschel in 1784) was given its nickname by astronomer Maurice Leyland for its triangular shape, like that of a Christmas tree, as seen through binoculars or a small telescope.  In the image above, the tip of the inverted “tree” is marked by the seventh magnitude star HD 47887 (just above the Cone Nebula as seen at the bottom of the image) with the bright variable star S Monocerotis (15 Monocerotis) to the north forming its “trunk”.

S Monocerotis is a bright irregular eruptive variable.  It is a multiple star system whose primary component is a hot, massive O-type star 10 times the size of the Sun and 30 times as massive.

The “Fox Fur Nebula” (Sharpless 273) can be seen below S Monocerotis in the above image.  Its resemblance to road-kill is quite remarkable, even in these modest images.  The bluish area arises from the reflection of starlight from dust in the region.  Some images show this reflection nebulosity to be much more extensive than seen here, probably because I did not compensate for the poorer blue sensitivity of the CCD with longer blue subs.

The Christmas Tree Cluster is visible to the naked eye in good conditions and appears quite striking in binoculars. The stars forming the Christmas tree shape, along with dozens of other tiny bright stars within the cluster, are a magical sight as seen in my VC200L with a 25mm eyepiece.  None of the associated nebulosity is visible however, at least, not to me.

NGC 2264 is listed as “Hidden Treasure 38” in Stephen O’Meara’s excellent book "Hidden Treasures" in the Cambridge University Press “Deep Sky Companion” series, the relevant excerpt from which can be found here.

M42 - The Great Orion Nebula...

Object: Messier 42 (NGC 1976)
Type: Emission Nebula
Constellation: Orion
Distance: 1340 light years

Date: 01 January 2018
Equipment: SXV-H9, Vixen 114mm f5.3 ED refractor, guiding with Lodestar X2/PHD

Subframes: 30 x 300s, 100s & 20s H-alpha, 20 x 20s & 100s RGB 2x2 binned, 20 flats for each channel, no darks (hot pixel removal in Astroart instead).

Images were acquired and pre-processed (aligned, stacked, denoised) in AstroArt, then composited in Paint Shop Pro.

The Orion Nebula presents quite a challenge to depict because of the wide brightness range of its key features. Many early CCD images of this object as shown on the web "burn out" the "trapezium" region of the four central stars in attempting to show the outlying nebulosity.

I use the "layers" function in PaintShop Pro, stacking the longest exposures on top of shorter ones, and then carefully use the "eraser" tool to remove overexposed areas, leaving the underlying correctly exposed regions to show through.  This has to be done with care to avoid introducing obvious processing artefacts.

The luminance (H-alpha) channel, processed as described above, is shown below:

Whilst the latest image processing programs such as Pixinsight have "dynamic range adjustment" features that can automatically produce an even distribution of brightness, some of the resultant images can seem rather strange to my eyes.  Programmes like that are way beyond both my budget and my understanding!

LRGB combination (using the H-alpha stack as the luminance channel) went well in both Astroart and PaintShop Pro. The PSP version was a lot greener than the Astroart one (which automatically weights colours given that most CCDs are more sensitive to green light than red or blue, I guess), but I preferred the PSP output as it hinted at the greenish hue of the nebula that is so clearly discernible though the eyepiece.

All of the brighter features seen in the above image show clearly through my VC200L and a 25mm eyepiece. The central trapezium of the four stars brilliantly shine against a bright silvery background, which fades into the convoluted greenish wings of the surrounding nebula.  The dark channel between the main portion of the nebula and the upper candle-flame is clearly seen.

I strove to retain all of these key features in the image above, as well as highlight the extended nebulosity that the eye cannot see.

More information about this object can be found here.

Comet C/2016 R2 (PanSTARRS)...

Click on image to enlarge

Object: Comet C/2016 R2 (PanSTARRS)
Constellation: Taurus
Distance: 2.1796 AU / 326 million km (at time of image)

Date: 19 January 2018
Equipment: SXV-H9, Vixen 114mm f5.3 ED refractor, guiding with Lodestar X2/PHD

Subframes: 30 x 120s luminance, 20 flats, no darks (hot pixel removal in Astroart instead).

Guiding and stacking using the comet as the reference point has produced trailing stars due to the orbital motion of the comet against the sky background.

Longer exposures through larger apertures (and by far more skilled imagers than I!) evidence much more tail structure than is apparent here.

I could not convince myself that I could actually see the comet through the eyepiece of the ED114, let alone detect the CO-induced blue colouration so evident on long exposure colour images.  

"Supermoon"...

Object: Moon
Distance: 356600 km
Constellation: Gemini
Date: 01 January 2018

Equipment: SXV-H9, Vixen 114mm f5.3 ED refractor,

Subframes: 300 x 0.004s H-alpha, no flats, no darks

Images were obtained via Astroart and then stacked and processed in Registax.

A "supermoon" is defined as a new or full moon which occurs when it is at (or within 90% of) its closest approach to Earth in a given orbit. Supermoons are not uncommon - there are usually between four and six a year on average.

This one is unusual, however, in that it came only 4.5 hours after the moon reached lunar perigee – the moon’s closest point to Earth in its monthly orbit. 

Of the 13 full moons and 14 lunar perigees occurring in 2018, this is the closest alignment of full moon and lunar perigee for the year.  This full moon therefore represents the largest and brightest supermoon of 2018.

M1 - The Crab Nebula...

Click on image to enlarge

Object: Messier 1 (NGC 1952)
Type: Supernova remnant
Constellation: Taurus
Distance: 6500 light years

Date: 27&28 December 2017
Equipment: SXV-H9, Vixen 114mm f5.3 ED refractor, guiding with Lodestar X2/PHD

Subframes: 30 x 300s H-alpha, 20 x 300s OIII, 20 flats for each channel, no darks

This object is clearly visible in my (200mm aperture) VC200L.  With averted vision some structure can be seen, even from my light-polluted sky. Visually, a dark notch on the eastern side of the nebula does give the object a passing resemblance to a crab's claw, although this is much less apparent on filtered CCD exposures than it is at the eyepiece.  I previously imaged this object in "white light" and the feature shows up quite well.

Subframes for this effort were acquired and preprocessed in Astroart.  I have started to use the hot pixel removal function rather than muck about with dark frames.  My ancient SXV-H9 is not actively cooled so the camera temperature (and hence dark noise) probably varies during an imaging session.  This seems to lead to odd artifacts over long sequences of exposures when using conventional dark frames.  Just hitting any hot pixels with the filter as part of preprocessing seems to a better job and is a lot less effort than making master darks.

For imaging M1, I decided to try colour imaging just based on H-alpha (as red channel) and OIII (as blue channel) data.  The first hurdle came when I looked at my OIII images.  I had not used this filter for CCD imaging before, and the images showed what seemed to be horrendous reflection rings around the stars (section enlarged below).

I contacted Astronomix, the filter manufacturer. They replied that the filter I had was for visual use only, and that the rings were due to it not being IR/UV blocked.  I am not so sure, but will try again sometime with a blocking filter in place.  For the purposes of this image however, I found that the situation was not irretrievable.

When I layered the bloated OIII image stack over the much sharper Ha data and blended in "darken" mode in PSP, this effectively subtracted out the halation, as below, giving a "clean" OIII channel.

To try and avoid the odd pink and blue stars that two colour-only channels seem to give in some instances, I decided to make an additional artificial green channel by layering the above image over the Ha stack and selecting the "multiply" option in PSP.  This allowed me to generate an RGB colour image, using the fake green channel, plus the above OIII image as blue and the Ha stack as red.  I then added the Ha stack back in as the luminance channel to give the final LRGB image.  A bit of tweaking in PSP (curves, cropping) gave the final image as shown at the top.

Quite how "valid" any of this is in terms of true colour is questionable of course, but I think it looks OK and not too unrealistic compared to what else is out there on the web.

The Crab Nebula is perhaps the most intriguing object in the deep sky realm.  Information about it can be found here.