Tuesday 10 December 2019

IC 405: The Flaming Star Nebula...

IC 405: The Flaming Star Nebula

Object: IC 405 (Caldwell 31, Sharpless 2-229)
Type: Emission and Reflection Nebula 
Constellation: Auriga
Distance: 1500 light years
Dates: 4th. and 9th. December 2019
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 20 x Red (300s), 20 x Green (300s), 20 x Blue (450s), 40 x 300s H-alpha: no flats/darks (hot pixel removal in Astroart).

IC 405 can be found in the constellation Auriga, high in the Orion Milky way in the south-eastern sky during early winter. It was discovered in 1892 by J.M. Schaeberie, M. Wolf and E. von Gothard on photographic plates while investigating Nova Aurigae 1891.

Stellarium map showing location of IC 405
IC 405 appears as a full-moon-sized glow surrounding the variable star AE Aurigae. It is extremely difficult to see visually from suburban skies with amateur telescopes.

It is located adjacent in the sky to another nebula, IC410, although the connection is merely a line-of-sight effect as IC 410 is a much more distant object.

The variable star AE Aurigae (indicated on the hydrogen alpha image below) is thought to be the source of the energy which illuminates the nebula, whose light is a mixture of fluorescence from ionised gasses (red) and reflected starlight from surrounding dust (blue).

Measurement of the star’s velocity suggests that it was not formed from this material.  Instead, AE Aurigae is believed to have originated in the vicinity of the Trapezium star-forming complex in Orion.  The star is thought to have once been part of a binary star system with a massive companion that went supernova, and whose expiry released it from its gravitational anchor, catapulting it from its birthplace around 2.5 million years ago.

Hydrogen alpha image of IC 405, with AE Aurigae indicated...

Its current velocity of approximately 35 miles per second will carry it through the five light year-wide cloud of gas and dust that forms IC 405 within the next 20,000 years, which will cease to shine once its illuminating star exits the region.

The Ha frames were gathered in the presence of an 80% gibbous moon located just 30° from the target. The RGB frames had been collected earlier without the bleaching effect of a bright moon.  Processing technique is described here.

Some 10 years ago I previously imaged this area with a 135mm camera lens to capture both IC405 and IC 410, and although the image is a low resolution one it does give an indication of their adjacency in the sky.

Wednesday 4 December 2019

Sharpless 2-142: The "Wizard" Nebula...

Sh2-142: The "Wizard" Nebula...

Object: Sharpless 2-142 (Sh2-142), with open cluster NGC 7380
Type: Emission Nebula and open cluster
Constellation: Cepheus
Distance: 9700 light years
Dates: 29th November, 2nd and 3rd December 2019
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 16 x 600s H-alpha, 16 x 600s SII, 16 x 600s OIII, no flats/darks (hot pixel removal in Astroart).

Sharpless 142 is a diffuse emission nebula surrounding the developing open star cluster NGC 7380. NGC 7380 was discovered by Caroline Herschel in 1787. William Herschel included his sister's discovery in his catalogue, and labelled it H VIII.77. The nebula itself is very faint and eluded the eagle-eyed Herschels.

Stellarium map showing location of Sh2-142
It can be found in the constellation of Cepheus, which is virtually overhead during autumn evenings in the UK. The nebula occupies an area approximately equal to that of the full moon, but is very difficult to see visually with telescopes, especially from suburban locations

The nebula spans about 140 × 75 light-years in space and lies within our Milky Way Galaxy.
 
The Sharpless designation comes from the Sharpless catalogue of 312 emission nebulae (H II regions). The first edition was published by Stewart Sharpless in 1953 with 142 objects (Sh1) and the second and final version was published in 1959 with 312 objects (Sh2).

The cluster and nebula are part of an even larger and optically invisible molecular cloud designated NGC 7380E, estimated to contain 6000-15000 solar masses of dust and gas.  It is believed that the star formation that created the stars of NGC 7380 began some 4 million years ago and continued for another 2 million years before it largely ceased, with radiation from the stars dispersing the cloud from which they formed and ionising the remaining gas to produce the emission nebula we see today.

Mist and freezing condensation terminated all three imaging sessions before midnight. Auto-guiding was also a pig, with an RMS of anywhere between 0.7 to 1.2, giving rise to rather poor resolution and bloated stars. I'm not sure whether that's down to the mount (balance seems absolutely critical) or poor seeing. The seeing certainly wasn't good for any of these sessions: I could see the focus star rippling violently whilst trying to get a sharp focus, which in the end just turned out to be a best guess. 

The Ha, SII and OIII frames were stacked in Astroart and then RGB combined in PaintShop Pro. A blend of 50: 50 SII/Ha was used for the red channel, 30:70 Ha/OIII for the green and 100% OIII for the blue, with further curve changes, star reduction and denoising in PSP to give the final image. This was the first time I had tried adding some SII data into the mix, and it certainly seems to add some contrast to the final image.

The colloquial name of “the Wizard” alludes to an apparent figure in a pointy hat that can supposedly be made out in the nebulosity but like so many of these more recent monikers, I’m not sure I can see it myself.  Maybe it looks more like Roy Wood....  

Wednesday 20 November 2019

NGC 281: The Eye of Sauron...

NGC 281 - The "Pac-Man" Nebula...

Object: NGC 281 (also commonly known as the Pacman Nebula, IC 11 or Sharpless 2-184 (Sh2-184), with open cluster IC 1590)
Type: Emission Nebula 
Constellation: Cassiopeia
Distance: 9200 light years
Date: 18th and 29th November 2019
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 25 x 300s H-alpha, 12 x 600s OIII, no flats/darks (hot pixel removal in Astroart).


Discovered in August 1883 by E. E. Barnard, NGC 281 is an emission nebula forming part of a larger HII region in the Perseus Spiral Arm of the Milky Way. Lying against the backdrop of constellation of Cassiopeia, it can be found virtually overhead on late autumn evenings but is extremely difficult to see visually in telescopes from suburban locations. 

Location of NGC 281 in night sky, looking north
At its centre, this faint, full-moon-sized nebulosity contains the open star cluster IC 1590, whose stars provide the radiation that causes the fluorescence of the surrounding gas cloud.  The nebula also contains several Bok globules, small dark dust clouds that can be seen in the image above. 

Colloquially, NGC 281 has suffered the misfortune to have been saddled with the ghastly, hackneyed moniker of “the Pacman Nebula” for its supposed resemblance to the eponymous character from the primitive 1980’s video game. 

The name actually put me off trying to hunt down this object, daft though that may seem.  It just seems so incredibly tacky (rather like the computer game) and certainly not something that should be associated with such a splendid and complex wonder of the night sky.

This particular evening was the first clear, dark night for over a month but as is always the way, the atmosphere was very unsteady.  I use an electronic focussing motor that I manually nudge to obtain a sharp star focus, but the image of the star could be seen to be twisting and flexing, making focussing very difficult.  The subsequent guiding of the telescope was thus also pretty poor, leading to bloated star images and I despaired of getting a decent result. 

Indeed, I packed it in after a couple hours. Nevertheless, some aggressive star reduction and sharpening in PSP yielded a reasonable hydrogen-alpha image (shown above).

NGC 281: hydrogen alpha data.

The RGB data was completed with the acquisition of some OIII data a week or so later (R = Ha, G = 70:30 OIII/Ha, B = OIII)  and the result recombined a colourised Ha luminance layer (technique described here) to give the image at the top.

By way of a counterpoint to the naffness of its accepted nickname, this image of NGC 281 is presented in a rotated format, with north to the right. I think that this orientation serves to draw the eye to the dramatic and highly-structured dark dust lane that runs across the face of the nebula and which resembles the pupil of a vast, sinister celestial eye – hence my title of this post: the Eye of Sauron…

This nickname has already been bagged by a dim and distant galaxy (11th magnitude NGC 4151) in the constellation of Canes Venatici.  NGC 281 is a much more accessible object, however, and does actually resemble (and deserves the link to) its cinematic avatar far more than the obscure galaxy does. I've since been told that the Helix nebula in Aquarius (NGC 7283) has also been called the "Eye of Sauron" (as well as the "Eye of God": conflating the two may be offensive to some folk!). The Helix is a long-standing and not-at-all-naff nickname which describes that large planetary nebula well, so giving it other names seems rather silly and pointless.

But I would dearly like to bury the "Pacman".  However, below is the nebula shown in its natural orientation, for those folk who are fans of naff eighties computer games.  Or just like seeing things the way they really are, at least in spatial terms (the colours are subjective, of course)...

NGC 281; Oriented with North up (as seen in sky)


Thursday 10 October 2019

Sharpless 2-132 - The Lion Nebula...


Object: Sharpless 2-132 (Sh2-132)
Type: Emission Nebula 
Constellation: Cepheus
Distance: 10400 light years
Date: October 8th and 9th, 2019
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 12 x 600s H-alpha, 10 x 600s OIII (2x2 binned), 5 each of 150s 2x2 binned for RGB star colour, no flats/darks (hot pixel removal in Astroart).

This image is centred on a patch of sky located at the borders of the two constellations Cepheus and Lacerta, which are high overhead in the Milky Way during mid-Autumn evenings. Sharpless 2-132 is another faint H-alpha emission nebula catalogued by Stewart Sharpless, and is located in the Perseus arm of our Milky Way galaxy.  At that distance, the gas cloud is calculated to occupy a volume of space about 250 light years across.

Stellarium sky map showing location of Sh2-132
The nebula has been nicknamed the "Lion" nebula and (at a push) the form of a heraldic Lion passant can just be made out.

The framing above has cut off the unfortunate beast's legs however, which are outlined as some extended OIII nebulosity, and which I will have to revisit in the near future.

Entangled within the Lion's mane is GP Cephei, a Wolf-Rayet star. This quintuple star system contains a super-massive component that has consumed all of its hydrogen and is now fusing helium, and is destined to explode as a supernova. It radiates strongly in the ultraviolet and is responsible for the ionisation and excitation of the gases forming the Lion's head and producing the characteristic fluorescence of hydrogen and oxygen ions that give the nebula its colour. The system has also shed distinctive shells of gas, that can be seen at the centre of the Lion's body.


Thursday 3 October 2019

Sharpless 2-101: The Tulip Nebula...


Object: Sharpless 2-101 (Sh2-101)
Type: Emission Nebula 
Constellation: Cygnus
Distance: 6000 light years
Date: October 2nd, 2019
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 10 x 600s H-alpha, 10 x 600s OIII (2x2 binned), 5 each of 150s 2x2 binned for RGB star colour, no flats/darks (hot pixel removal in Astroart).

This image captures a section of the Milky Way just to the east of Eta Cygni, a third magnitude star in the neck of the constellation of Cygnus the Swan.  Within it is a HII emission nebula popularly called the Tulip Nebula, a glowing red cloud of interstellar gas and dust recorded by astronomer Stewart Sharpless in his 1959 catalogue as Sh2-101.

Stellarium sky map showing location of Sh2-101
The bright star near the centre of the nebula is HDE 227018, and is believed to be the primary source of ionising radiation that lights up the nebula.  Also framed in the field of view is Cygnus X-1, one of the strongest X-ray sources in our sky. Driven by powerful jets from a black hole accretion disk, its fainter visible curved shock front is just visible in the above image as a faint bluish arc to the west (right) of the Tulip's petals.

Cygnus X-1 is a binary star system and a strong source of X-rays that provided the first major evidence for the existence of black holes. The primary star, HDE 226868, is a hot supergiant star revolving around an unseen companion with a period of 5.6 days. Analysis of the orbit led to the finding that the companion has a mass of nearly nine solar masses. A star of that mass should have a detectable spectrum, but the companion does not.  From this and other evidence astronomers believe that it must therefore be a black hole.  The X-ray emission is understood as being due to matter torn from the primary star that is being heated as it is drawn to the black hole.

In the case of Cygnus X-1, perhaps little of that matter actually makes it into the black hole. In-falling gas may first collide not only with itself but with an accretion disk of swirling material surrounding the black hole.  The result may be a microquasar that glows across the electromagnetic spectrum and produces powerful jets that expel much of the in-falling matter back into the cosmos at near light speed before it can even approach the black hole's event horizon.  Confirmation that black hole jets may create expanding shells has come recently from the discovery of shells surrounding Cygnus X-1. 


A section of the main image is shown above, showing a trace of one such shell quite possibly created by the jet of microquasar and black hole candidate Cygnus X-1. The area within the circle has been stretched a bit in the blue channel to help the arc of hot gas stand out.

Seeing was not particularly good on this evening, and the guiding of the telescope was a bit erratic (around 0.9 RMS – the current autoguider settings had previously achieved 0.4 RMS). Sh2-101 is also a fairly faint object, and it could have done with more and longer subframes than I had patience for. 

The resultant narrowband image stacks were rather noisy and the stars a little bloated. The OIII emissions from the nebula are quite weak and I had to stretch the stack quite a long way to get the bluish colour to show through in the final image. Nevertheless, they cleaned up reasonably well in PSP and were RGB combined in PSP using the Ha stack as the red channel and the OIII stack as the green and blue channels. The RGB stars were added as a layer in “lighten” mode.

After all that I was quite surprised and pleased to have captured the shells from Cygnus X-1. 

Saturday 28 September 2019

Messier 27 - The Dumb-bell Nebula...

M27 (NGC 6853) - the "Dumb-bell" Nebula 
Object: Messier 27 (NGC 6853)
Type: Planetary Nebula 
Constellation: Vulpecula
Distance: 1200 light years
Date(s) of imaging: September 19th, 27th and October 27th 2019
Equipment: ATIK 460EX, Skywatcher f5.5 Espirit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 20 x 300s + 16 x 1200s H-alpha, 20 x 300s + 16 x 600s + 16 x 1200s OIII, 6 x 180s (2x2 binned) each for RGB star colours, no flats/darks (hot pixel removal in Astroart).

M27 was the first planetary nebula to be discovered (in July 1764, by Charles Messier) and is one of the nearest and brightest of its type.  It can be found in the dim constellation of Vulpecula, sitting within the Summer Triangle of the three bright stars Vega, Deneb and Altair.  Its physical diameter, (estimated to be around 1.2 light years) also makes it one of the largest.

It gets its popular nick-name of the "Dumb-bell" nebula by its allegedly telescopic appearance to a weight-lifter's dumb-bell, the view lacking the OIII "ears" shown in the above image.

Planetary nebulae have nothing to do with planets.  The term is likely derived from their often round, planet-like shape as observed by astronomers through early telescopes, and although the terminology is inaccurate, it is still used by astronomers today.

To early observers with low-resolution telescopes, M27 and other subsequently discovered planetary nebulae resembled the giant planets like Uranus, appearing as pale blue or green discs with a similar visual diameter to the solar system’s gas giants.

The true nature of these objects was uncertain, and Herschel first thought the objects were stars surrounded by material that was condensing into planets.

It wasn’t until the first spectroscopic observations were made in the mid-19th century that the true nature of planetary nebulae became apparent, when William Huggins became the first scientist to analyze the spectrum of a planetary nebula when he observed the Cat's Eye Nebula.

Huggins’s earlier observations of stars had shown that their spectra consisted of a continuum of radiation with many dark lines superimposed.  He found that many nebulous objects such as the Andromeda Nebula (as it was then known) had spectra that were quite similar.  However, when Huggins looked at the Cat's Eye Nebula, he found a very different spectrum.  Rather than a strong continuum with absorption lines superimposed, the Cat's Eye Nebula and other similar objects showed a number of emission lines, similar to those produced by fluorescent gases.  It was clear that these nebulae were neither planetary in nature, nor composed solely of stars.

Brightest of the emission lines was at a wavelength of 500.7nm, which did not correspond to a line of any known element.  At first, it was hypothesised that the line might be due to an unknown element, which was named “nebulium”. A similar idea had led to the discovery of helium, through analysis of the Sun's spectrum in 1868.  While helium was isolated on Earth soon after its discovery in the spectrum of the Sun, "nebulium" was not.  

Physicists subsequently found that in gas at extremely low densities, electrons can occupy excited metastable energy levels in atoms and ions that would otherwise be de-excited by collisions that would occur at higher densities.  Electron transitions from these levels in ionised nitrogen and oxygen ions (rather than an “unknown” element) give rise to the 500.7 nm emission line and others. These spectral lines, which can only be seen in very low density gases, are called forbidden lines. Spectroscopic observations thus showed that nebulae were made of extremely rarefied gas.

The above image shows the strong blue and red colours, associated with the fluorescence of ionised oxygen and nitrogen respectively.

All planetary nebulae form at the end of an intermediate massed star's lifetime. They are a relatively short-lived phenomenon, lasting perhaps a few tens of thousands of years at the very end of a star’s life cycle.  Once all of a red giant's atmosphere has been dissipated, energetic ultraviolet radiation from the blazingly hot (>50,000K) exposed hot luminous stellar core ionises the ejected material.  Absorbed ultraviolet light then energises the shell of nebulous gas around the central star, causing it to fluoresce and give rise to the brightly-coloured light emissions of a planetary nebula.

Only when a star has exhausted most of its nuclear fuel can it gravitationally collapse to a small size, losing the outward radiation pressure that supports it. Planetary nebulae came to be understood as a final stage of stellar evolution.  Spectroscopic observations show that all planetary nebulae are expanding. This led to the idea that planetary nebulae were caused by a star's outer layers being thrown into space at the end of its life.

About 3000 planetary nebulae are now known to exist in our galaxy, out of 200 billion stars.  Their very short lifetime compared to total stellar lifetime accounts for their rarity. They are found mostly near the plane of the Milky Way, with the greatest concentration near the galactic centre.

Only about 20% of planetary nebulae are spherically symmetrical. A wide variety of shapes exist with some very complex forms seen.  The huge variety of shapes is partially due to the orientation of our planet to the nebula - the same nebula when viewed under different angles will appear different.  Nevertheless, the reason for the huge variety of physical shapes is not fully understood.  Gravitational interactions with companion stars if the central stars are binary stars may be one cause. Another possibility is that planets disrupt the flow of material away from the star as the nebula forms. It has been determined that the more massive stars produce more irregularly shaped nebulae.

In January 2005, astronomers announced the first detection of magnetic fields around the central stars of two planetary nebulae, and hypothesized that the fields might also be partly or wholly responsible for their remarkable shapes.

This image was compiled from data collected on three different nights, dodging autumn clouds and the moon. The OIII and “Hydrogen Alpha” (the majority of the "red" emissions are actually from ionised nitrogen, whose emission wavelength is close to that of H-alpha radiation), were stacked separately in Astroart and then RGB combined in Paint Shop Pro (Red = Ha, Green and Blue = OIII).

My first attempt was satisfactory but did not really show the faint outer regions of the nebula (see below):

M27, 300+600s narrowband exposures
I was determined to try and capture the faint secondary shell surrounding the nebula, the relic of an earlier out-gassing episode. It seemed that my initial data-set just didn't have long enough exposure times to register these very faint extensions, so I took some additional 1200 second exposures at the first moon-free opportunity (this is about as long as I can go at my light-polluted location without the sky background washing everything out). The long-exposure stacks still required some aggressive selective stretching (and subsequent star reduction) to bring the "wings" out, but after a bit of trial and error in PaintShop, I was quite pleased with the final result (top image). A few binned RGB frames were RGB combined in Astroart and the output subsequently blended with the HOO frame to give some colours to the stars.

M27 - wide field including 1200s narrowband data
The main image is a crop of the wide field original, shown above.

I had previously imaged M27 way back in July 2005. One interesting feature of that image compared with my latest one is that it shows the presence of an additional star. The older data (to which this year's colour data was added to make visual comparisons a bit easier) was broadband as against narrowband and so the stars are inherently brighter, but the absence of the star in the later image is still apparent.

Old and new images of M27, showing variable star
The variability of this star was first discovered in 1988 by Leos Ondra, a Czech amateur astronomer, who noticed that the star appeared in some images of M27 but not in others. He concluded that it was a long period variable and nicknamed it “Goldilocks”.

The Goldilocks Variable was later confirmed to be a Mira-type variable, a pulsating star going through a cycle of expansion and contraction every 213 days. Mira variables were named after the first star observed to have such properties, known by its Bayer designation Omicron Ceti, a red giant star located in the constellation Cetus.

The Goldilocks Variable is not within the Dumbbell Nebula, but is a background object much further away.

Sunday 8 September 2019

Eastern Veil Nebula (NGC 6992-5)

Eastern Veil Nebula (NGC 6992-5)

Object: Eastern Veil Nebula (NGC 6992-5)
Type: Emission Nebula (supernova remnant)
Constellation: Cygnus
Distance: 1470 light years
Date: September 7th, 2019
Equipment: ATIK 460EX, Skywatcher f5.5 Espirit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 16 x 300s H-alpha, 3 x 300s OIII, no flats/darks (hot pixel removal in Astroart).

The nebula was discovered telescopically on 1784 September 5 by William Herschel.  He described the western end of the nebula as "Extended; passes thro' 52 Cygni... near 2 degree in length", and described the eastern end as "Branching nebulosity... The following part divides into several streams uniting again towards the south."

The Veil Nebula is part of a much larger supernova remnant, believed to have formed when a star 20 times more massive than our Sun, exploded around 8,000 years ago.  The remnants have since expanded to cover an area of the sky roughly 3 degrees in diameter (about 6 times the diameter, or 36 times the area, of the full Moon).   The distance to the nebula is not precisely known, but Far Ultraviolet Spectroscopic Explorer (FUSE) data supports a distance of about 1,470 light-years.

The nebula appears as a streamer of fine filaments. The standard explanation is that the outgoing shock wave from the original supernova is heating a shell of residual hydrogen gas and the wave-front is visible only when viewed exactly edge-on, giving the shell the appearance of a filament.  Given a distance of 1470 LightYears, this gives the radius of the entire nebula as 38.5 Light Years (totalwidth, 77 Light Years). At 1/50,000th of the radius, this places the thickness of each filament at around 4 billion miles, or roughly the distance to Pluto.  Undulations in the surface of the shell leadto multiple filamentary images, which appear to be intertwined.

Even though the nebula has a relatively bright integrated magnitude of 7, it is spread over so large an area that the surface brightness is quite low.  It is very hard to see visually from suburban locations, although use of an OIII filter is said to help.

The brighter segments of the nebula have the New General Catalogue designations NGC 6960, 6974, 6979, 6992, and 6995. The easiest segment to find is the Western Veil Nebula NGC 6960, which runs behind the naked eye star 52 Cygni. NGC 6992 and 6995 are also relatively bright objects on the eastern side of the loop. NGC 6974 and NGC 6979 are visible as knots in an area of nebulosity along the northern rim.  Pickering's Triangle, a triangular area of nebulosity between the east and western nebulae, is much fainter and has no NGC number.  It was discovered photographically in 1904 by Williamina Fleming (after the New General Catalogue was published), but credit went to Edward Charles Pickering, the director of her observatory, as was the custom of the day.

Over ten years ago, I managed to photograph the whole of the "Cygnus Loop" using a 135mm camera lens and my old SXV-H9 CCD camera.  The result can be seen here.

The Eastern Veil Nebula is easy to find, tucked just in front of the eastern wing of Cygnus the Swan. The constellation of Cygnus flies high in the southern sky in late summer, with its brightest star Deneb being one of the three bright stars that form the "Summer Triangle".

I had planned to take 16 300 second exposures through H-alpha and OIII filters, but clouds rolled in and I only got three OIII frames.

The separate channels were stacked in Astroart and then RGB combined, using the H-alpha as the red channel and the OIII data as the green and blue channels. The image was a bit noisy due to the lack of subframes, but using the H-alpha data as a luminance overlay to the smoothed RGB channel helped sharpen up the final image.

This was the first test run of my new Esprit 100ED refractor, coupled with a second-hand Avalon Linear mount. The mount performed pretty well after some initial problems with PHD settings, settling down to give an RMS figure of around 0.6, which was much better than my old NEQ6, which usually could only manage 0.8 at best.

I cannot say that the Esprit performed any better than my old Vixen ED114 in narrowband, however. I had hoped that the relatively small field of view offered by the Atik 460 would mean I didn't need to use a field flattener, with all of the critical requirements of camera spacing that requires. Unfortunately, there was a fair bit of star distortion in the corners of the final image, that I manually processed out.

I will see how the scope performs in RGB, but I could well be reinstating my old Vixen...


Wednesday 17 July 2019

Partial Lunar Eclipse...

Partial lunar eclipse, approx. 22.15 BST
Object: Moon
Constellation: Sagittarius
Distance: 398865 km (247843 miles)
Date: June 16th, 2019
Equipment: Canon 450D, Celestron NexStar 4
Subframes: Approx 30, ranging from 0.1s to 2s @ ISO800

The Moon was only 7 degrees above the horizon when I took images for the above composite.  The partial eclipse began with the moon entering the Earth's shadow at 9 pm, just as it was appearing above the horizon. Maximum eclipse was at 20.30, with the Moon leaving the Earth's umbral shadow at midnight.

The low altitude meant the focussing was tricky and a lot of lunar detail was blurred by the unsteady atmosphere so close to the horizon, along with some wispy clouds. I took a range of exposures to try and capture details on the illuminated portion of the moon and also to try and show the eclipsed area, whose glow was quite distinct in binoculars. 

I used Registax and PaintShop Pro to pull together the best shots from around 30 images taken with various exposures. With a lot of messing around, I managed to combine the image sets into something that resembled the view through binoculars.

Saturday 30 March 2019

M101 - The Pinwheel Galaxy...


Object: M101 (NGC 5457)
Type: Spiral Galaxy (morphological classification SAB (rs) cd)
Constellation: Ursa Major
Distance: 20.9 million light years
Date: March 29th, 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 16 x 300s each for RGB, flats but no darks (hot pixel removal in Astroart). Above is a 50% crop of the original image.

Messier 101 (M101), also known as the Pinwheel Galaxy, is a spiral galaxy located in the constellation Ursa Major. It has the designation NGC 5457 in the New General Catalogue. Discovered by Pierre Méchain on March 27, 1781, it was communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final entries.

M101 lies at a distance of 20.9 million light years from Earth. The galaxy appears face-on and occupies an area of 28.8 by 26.9 arc minutes of apparent sky (about the same size as a full moon), which corresponds to a linear diameter of about 170,000 light years, similar to our Milky Way galaxy. 

Its location in the sky is easy to find, forming an equilateral triangle with Mizar and Alkaid, two of the bright stars in the “handle” of the Plough (see the Stellarium map opposite). Despite this, the galaxy has a low surface brightness that renders it difficult to see from suburban locations.

M101 has around a trillion stars, more than twice the number of stars in the Milky Way. The galaxy has an unusually high number of H II regions, where new stars form, and many of these regions are bright and large, ionized by many extremely luminous and hot young stars.  Some of the larger and brighter ones can be seen in the above image.

Sky conditions were not good on the night of the 29th.  Although cloud and moon-free, unusually calm conditions had allowed a build-up of a rather unpleasant pollution haze in the Medway Valley, with particulates exceeding recommended annual means as evidenced on the local UKAIR monitoring site (by a factor of four on  the 30th – which mercifully dispersed with the advent of northerly winds next day).  This gave a sickly orange colour to the sky, making it very difficult to pull out luminance data from the background sky glow, to the point where I gave up and stuck with the RGB filtered sub-frames, which were not so badly contrast-compromised.

If I get the opportunity, I will try and improve the brightness and resolution of this image by the acquisition of some longer (and hopefully cleaner) luminance exposures.

Monday 25 February 2019

The Rosette Nebula (NGC 2237-8, 46) with star cluster (NGC 2244)


Object: NGC 2237-8, 46 (nebula, Caldwell 49), NGC 2244 (open cluster, Caldwell 50)
Type: Emission nebula
Constellation: Monoceras
Distance: 4900 light years
Date: February 23rd, 24th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 36 x 300s H-alpha, 15 x 200s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

The Rosette Nebula (also known as Caldwell 49) is a large H II region located near one end of a giant molecular cloud in the Milky Way galaxy region lying in the constellation of Monoceros.  The nebula has an apparent diameter of over a degree, more than twice the diameter of the full moon.  The open cluster NGC 2244 (Caldwell 50) is embedded within the nebulosity, and is easily seen in a small telescope.  The nebulosity itself is too faint to be seen visually from suburban skies, however.

The constellation of Monoceros is rather dim and ill-defined, lying to the east of its brilliant neighbour Orion.  The location of the Rosette is shown on the Stellarium sky map below:

Interestingly, recent research suggests that the shape of the Rosette nebula is a disc that is (rather fortuitously) orientated face-on to our Earth, rather than a sphere. 

Radiation from the hot young stars of NGC 2244 is sweeping out the gas from the centre of its parent nebula, an effect that can be quite easily seen in the above image.  Researchers at the University of Leeds have found that this cavity is far smaller than it should be given the age and mass of the cluster stars, and have proposed that a combination of magnetic field orientation and a disc-shaped cloud best accounts for the current appearance of the nebula.

The cluster and nebula measure roughly 130 light years in diameter.  The radiation from the cluster stars within the nebula causes the surrounding rarefied gases to fluoresce, producing the visible emission nebula.  The mass of the nebula is estimated to be around 10,000 solar masses.

A survey of the nebula with the Chandra X-ray Observatory has revealed the presence of numerous new-born stars inside the Rosette Nebula.  Altogether, approximately 2500 young stars lie in this star-forming complex.  Most of the ongoing star-formation activity is occurring in the dense molecular cloud to the south east of the bubble.

In his excellent book The Caldwell Objects, Steve O’ Meara corrects the still-widespread errors regarding the discovery and cataloguing of the Rosette Nebula. O’Meara credits the discovery of the Rosette’s central cluster, NGC 2244, to William Herschel, who unambiguously recorded the object in 1784.  The surrounding nebulosity was not seen by the eagle-eyed Herschel, but was discovered later in a piecemeal fashion – a testament to the faintness of it.  Albert Marth discovered a part of the bright north-west segment of the nebula (NGC 2238) in 1864, with E.E. Barnard recording a larger part of the same quadrant in 1883 (although Lewis Swift had actually observed it several years earlier).  In 1886, Swift found the bright patch of nebulosity in the eastern quadrant of the Rosette (NGC 2246), but it was not until the early 1890’s that photography showed the full extent of the nebula.

My image clearly shows the dark Bok globules that are strewn across the face of the Rosette.  The “globules” comprise of gas and dust, slowly coalescing from the surrounding nebula under its own forces of gravitational attraction, and are thought to be the birthplace of new stars and planets.


One of these curious areas, which stands out in the northern arch of the Rosette, resembles a leaping cat.  I’m not sure it has a common name or designation, but I have picked it out in the hydrogen alpha image stack, shown above.

I think the whole nebula resembles the skull of a fossilised pre-human, such as pithecanthropus, with the cluster NGC 2244 sitting in its left eye socket.

Colour image processing for the main image was conducted using my usual methods in AstroArt and PaintShop Pro, which are detailed here.

This is a bit of an improvement on my first attempt at imaging this object some 12 years ago. 

Friday 15 February 2019

NGC 884 and NGC 869: The Double Cluster...


Objects: NGC 884 and NGC 869 (The "Double Cluster", Caldwell 14)
Type: Open Clusters
Constellation: Perseus
Distance: 7500 light years
Date: February 14th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 20 x 300s luminance, 12 x 200s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

Known since antiquity, the “Double Cluster” was catalogued in 130 BC by Greek astronomer Hipparchus, who referred to it as a “nebula” or “cloudy spot”, one of the half a dozen then recognized.  The starry nature of the clusters remained a mystery until the invention of the telescope in the early 1600’s.

Now known respectively as h and chi Persei, or NGC 884 (to the east, or left, of the image) and NGC 869 (the cluster to the west, or right, of the image), the clusters themselves are separated by only a few hundred light-years and contain stars much younger and hotter than the Sun. 

In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product of the same star-forming region.  NGC 869 has a mass of 3700 solar masses and NGC 884 weighs in at 2800 solar masses; however, later research has shown both clusters are surrounded with a very extensive halo of stars, with a total mass for the complex of at least 20,000 solar masses. 

Based on their individual stars, the clusters are relatively young, both 12.8 million years old.  There are more than 300 blue-white super-giant stars in each of the clusters.

Discernible with the naked eye under dark skies, NGC 869 and NGC 884 occupy an area of sky approximately one degree across, each cluster being physically around 35 light years across. Binoculars are required to see the two clusters as separate entities from suburban skies. Telescopically, this is one of the most popular of objects for visual astronomers. It forms the “sword handle” of Perseus, as shown in the Stellarium star chart below:

This particular evening was clear but a bright gibbous moon was parked high in the sky, thus ruling out any attempt at faint nebulous objects. Processing was straightforward, with the RGB stacks combined in Astroart to give a colour image with pleasing and contrasting star colours. Some of the brighter stars have haloes, possibly caused by reflections from the RGB filters: Pixinsight acolytes would no doubt sneer at such things, but I quite like the effect.

Addition of the stacked luminance data as a luminance layer in PaintShop gave the final image above.  I used a star mask to just slightly drop the luminance and sharpen the stars surrounding the two clusters, just to get the clusters to stand out from the starry background a bit more.

Monday 11 February 2019

IC 443: The Jellyfish Nebula...


Object: IC 443
Type: Supernova remnant
Constellation: Gemini
Distance: 5000 light years
Date: February 10th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 16 x 600s H-alpha, 6 x 150s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

Discovered on September 25th, 1892 by German astrophotographer Max Wolf, IC 443 is a supernova remnant in the constellation Gemini, produced by a supernova explosion thought to have occurred between 3,000 and 30,000 years ago.  Physically, the nebula is about 70 light years across. Visually it appears to be approximately 50 arc-minutes across, an area of sky just under twice the apparent size of the full moon.  It is not readily seen in backyard telescopes.

The location of IC 443 is shown in the Stellarium sky chart below, just to the east of the third magnitude star Eta Geminorium (named Propus, the bright orange star to the right of the image).

Observations from the Chandra X-ray observatory show that the explosion that created the Jellyfish Nebula may have also formed a peculiar object located on the southern edge of the remnant, called CXOU J061705.3+222127, or J0617 for short. The object is likely a rapidly spinning neutron star, or pulsar, representing the end stage of a star with between 1.4 and 3 solar masses  

When a massive star runs out of thermonuclear fuel, it implodes, forming a dense stellar core called a neutron star.  The outer layers of the star collapse toward the neutron star then bounce outward in a supernova explosion.  


A spinning neutron star that produces a beam of radiation is called a pulsar.  The radiation sweeps by like a beacon of light from a lighthouse and can be detected as pulses of radio waves and other types of radiation.

The comet-like shape of the diffuse X-ray emission suggests motion towards the lower right of the image.  The structure is also evidenced at visible wavelengths, as highlighted in the hydrogen alpha image below:


The orientation of the “line” is about 50 degrees away from the direction expected if the pulsar was moving away from the centre of the supernova remnant in a straight line.

This misalignment has cast some doubt on the association of the pulsar with the supernova remnant. 

However, it is thought that this misalignment could also be explained by movement towards the left of material in the supernova remnant pushing J0617's cometary tail aside.



Seeing conditions and atmospheric clarity were excellent on this particular evening. I was able to grab 16 hydrogen alpha frames before the dreaded "meridian flip" (where the object crosses the east/west line, requiring the telescope to be spun round to prevent it hitting its own pier).  This is a pain and requires the telescope to be re-targetted, although fortunately my set-up usually gets the object back on the CCD chip after the flip, requiring only minor adjustments to re-frame the object on the CCD chip.

Given that the weather forecast was threatening clouds, I decided to grab the RGB frames rather than get more H-alpha data, although 16 subs isn't really enough to beat the background noise down.  My luck held, and I got the last of the blue subs just as a few clouds started to roll in at around midnight.

Colour processing was conducted using the same methods as I used for the Cave Nebula.

Tuesday 29 January 2019

IC 410: The "Tadpoles" Nebula...

IC 410 and NGC 1893... 
Object: IC 410 (nebula), with NGC 1893 (star cluster)
Type: Emission nebula with open cluster
Constellation: Auriga
Distance: 12000 light years
Date: January 29th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 16 x 600s H-alpha, 10 x 600s OIII, 6 x 150s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

IC 410 is an emission nebula partly obscured by dark, dense molecular clouds, and forms part of a larger star forming region that also contains the Flaming Star Nebula (IC 405, which lies approximately 1.5 degrees to the west of IC 410).  The cluster within, NGC 1893, was discovered in 1827 by John Herschel, but the surrounding nebula IC 410 was not detected until 1892, by German astronomer and astrophotographer Max Wolf.

The nebula occupies an area in the sky approximately 40 arc-minutes in diameter (a bit larger than the full moon). In reality, the nebula is approximately 100 light years across. Visually,I was once lucky enough to just about make out the brightest areas of IC 410 in an 9.25-inch SCT on a night of excellent transparency from a suburban sky. The cluster NGC 1893 appeared to be enmeshed in a faint haze of nebulosity, with fainter lobes to the west and south of the cluster that required a low power (40mm) eyepiece and an OIII filter to provide the necessary contrast. It is not surprising that John Herschel missed it visually.  

IC410 is illuminated by fluorescence caused by the excitation of its gaseous atoms by radiation from the hot stars of the open star cluster (NGC1893) that lies in the centre of the nebula that gave birth to it.  This star cluster is about 4 million years old, but in astronomical terms it is still very young. 

The "tadpoles" of IC 410 (detail from main image)
At the top-left of the star cluster in the image, two columns of dust and gas left over from the formation of the star cluster can be seen.  These objects are designated as Simeis 130 – the lower of the two – and Simeis 129 (the rather obscure Simeis catalogue of nebulae arises from the Crimean Astrophysical Observatory, which has a facility in the town of Simeis in the Ukraine) and are popularly referred to as “the tadpoles”. These structures are thought to contain embryonic stars hidden in the dust and gas that enshrouds them.  As can be seen in the image, the heads of the “tadpoles” are outlined by bright ridges of ionised gas, while their tails trail away from the cluster's central region, evidence of the stellar winds and intense radiation pressure from the stars of NGC 1893.


IC 410 can be found high in the Orion Milky Way in the constellation Auriga, as indicated in the Stellarium sky chart below:

The striking green/blue colour visible in the main image arises from the fluorescence of triply-ionised oxygen atoms (OIII) which seems to be unusually strong in this particular nebula (the orange/red is from ionised hydrogen – Hydrogen alpha emission – which is the principle light given off by most emission nebulae).

Atmospheric stability and clarity were rather poor when I acquired data for the image, but this was the first clear spell that I had been able to make use of in the last six weeks, so beggars can’t be choosers.  The guiding wasn’t brilliant (about 1.2 arc-seconds RMS) and the resultant sub-frames were also very “noisy” due to a high haze of moisture that cut my gathering of OIII subframes short.

Fortunately, the signal was pretty strong in both Ha and OIII and the image stacks, although few in number, did not require much of a stretch.  

The narrowband colour data was RGB combined in Astroart (red = Ha, green =70/30 OIII/Ha, blue = OIII).  The RGB frames were also RGB combined and the result blended with the narrowband stack in PSP to give star colours.