The Gamma Cassiopeiae nebula...

 

IC63 and IC59

Object: IC59, 63 (Sharpless 2-185)
Type: Emission and reflection nebulae 
Constellation: Cassiopeia
Distance: 600 light years

Date: November 2nd, 3rd, 4th, 15-16th. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 47 x 600s Ha, 10 x 600s each for RGB (2x2 binned), flats, no darks (hot pixel removal in Astroart).

IC63 (the bright, pointed object near the middle of the image) and IC59 (the fainter bluish area above and to the upper right) are the brightest areas of the nebulosity known as Sharpless 2-185 (Sh2-185). They were discovered independently by Max Wolf (Dec 30, 1893) and Edward Barnard (Feb 2, 1894). 

Together, the nebulae occupy an area of space approximately 10 light-years across. 

The bright, hot star Gamma Cassiopeia (seen at the bottom right of the above image) is located only 3 or 4 light-years from the nebulae, and it may have shed this nebulous material into the space around it. The edges of the nebulae glow brightly from this intense radiation that is slowly evaporating and lighting up these flowing shapes of gas and dust 

Gamma Cassiopeia has a radius 14 times greater than our Sun and is 55,000 times more luminous, 19 times more massive, and rotates at about 300 km/hour, or 150 times more rapidly than our Sun. It is known as an eruptive blue-white sub-giant variable star. (Eruptive variable stars vary in brightness because of violent processes and flares in their coronae and chromospheres.) 

This star is an erratic variable that reached a maximum brightness in 1937, but then unexpectedly dropped in surface temperature from 12,000°K to 8500°K. It is encircled by a surrounding gaseous disk of material thrown off by its rapid rotation. Mass loss is apparently related to the brightness variations. 

Stellarium map showing image field

The constellation of Cassiopeia can be found virtually overhead during late autumn evenings (see map opposite). IC 63 (the brighter of the two and slightly closer to Gamma Cassiopeia than IC 59) is a combination of an emission and reflection nebula. Unlike a reflection nebula which appears blue, the glowing hydrogen gas appears red. IC 59 is primary a refection nebula, showing much less red hydrogen, and is appearing blue of dust reflected starlight that is passing through it. 

As can be seen above, the two nebulae have very different visual appearances. IC63 can be referred to as a "cometary cloud", is pointing toward Gamma Cas, and is narrower and more sharply defined than IC59. Spectral measurements suggest that IC59 is slightly cooler at 590K and less dense than IC63 at 630K. They are not actually separate nebulae, but are part of a much larger nebulous region surrounding Gamma Cas based upon the WHAM (Wisconsin H-alpha Mapper) survey. IC63 has bright filaments, visible in the image above, that are believed to be ionized fronts of gas created by Gamma Cas, and seen by us as nearly edge-on. 

Both nebulae exhibit spectroscopic evidence from the mid-infrared of molecular hydrogen and polycyclic aromatic hydrocarbons (PAH). The contrast in appearance between IC63 and IC59 is consistent with a difference in actual distances from Gamma Cas and small differences in temperature and column density..

There is some discussion in professional circles as to whether the H-alpha signal that we pick up in our images is actual emission from the nebula, or a reflection of the H-a emitted from Gamma Cas that is scattered by the dust in IC59 and IC63. This light scattering and reflection is called ERE, (Extended Red Emission). Gamma Cas is the prototype B0 IV star, emitting significant H-a. It is above the main sequence with a more extended atmosphere. Being somewhat cooler than a BO V star, it is only marginally capable of ionizing molecular hydrogen in its vicinity. Thus, it is possible that the H-a we pick up in our images is a mixture of both processes; direct H-a emission from ionization, and ERE. 

H-alpha data was gathered on the bright moonlit evenings of 2-4 November. The bright (and damp!) conditions were not ideal for the imaging of what is quite a faint nebula, but given that the previous month’s skies had been completely clouded out, it seemed best to make do.  All three evening sessions were ended at around midnight due to high haze and mist setting in, and the resultant image stack suffered from background noise. 

Application of Starnet++ to the Ha stack allowed the nebulosity to be stretched and smoothed, with stars from the “unstretched” stack being pasted back in in “screen” mode to avoid star bloat. 

Colour data was acquired on 15-16^th November, with the moon mercifully absent: the imaging session was still stop-start due to clouds and was finally clouded out at around 2.00 am. 

The blue reflection nebulosity was pretty faint but once again Starnet++ allowed separation of the nebulosity from stars for processing purposes.  The Ha data was blended in with the red channel and the blend used in an RGB composite in PSP.  A partial luminance overlay of Ha was used to sharpen the image up a bit. 

References: 

1.         Astrodon imaging 

2.         NASA APOD 

3.                Anne’s Astronomy News 

4.         https://cseligman.com/text/atlas/ic0a.htm

Mars...

 

Mars, showing rotation over 90 minutes

Object: Mars
Type: Planet 
Constellation: Pisces
Distance: 45 million miles

Date: November 7th. 2020
Equipment: Phillips TouCam Pro, x2 barlow, Celestron C9.25, Vixen GPDX mount

Subframes: 15 images, each compiled from 1000 frames shot at 30 fps and aligned/stacked/wavelet processed in Registax v2.

The above gif is made from a series of images of Mars, and shows the rising of the feature of Martian geography known as Sirtis Major over the eastern limb of the planet over a period of about 90 minutes.

The evening of November 7^th was a foggy, soggy one, but Mars was very visible above the vapours and the evening represented one of the few opportunities I had to try and photograph the planet during its current opposition. 

Mars made its most recent close approach to Earth on October 6^th, when it was 38.5m miles away and appeared around 23 arc-seconds across in the sky. It won’t get that close again until September 2035, an event I am unlikely to witness. 

The closest Mars ever gets to Earth is about 34.5 millions miles and thus never appears to be more than around 25 arc-seconds across, effectively still looking like a bright star. Bear in mind that the full Moon is around 30 arc-MINUTES across and you can see how stupid social media stories of “Mars as large as the full moon” really are. 

Although a month past opposition, Mars was still a respectable 18.8 arc-seconds across and at magnitude -1.9, was brighter than any star and nearly as bright as Jupiter, which was setting in the west. 

To photograph Mars, I set up my old Celestron C9.25 SCT, and used an ancient (c. year 2000) Phillips TouCam Pro webcam as the image capture device. 

Planetary details are extremely small and views are constantly distorted by atmospheric fluctuations. Using a video camera to record 20 or 30 frames a second for a minute or so gives a bank of thousand or so pictures that can be processed by software (I use Registax) that selects the sharpest few frames and stacks them together to give a detailed result – in theory. In addition, Mars has a day that is about the same length as Earth’s and it therefore rotates quite quickly: a video longer than about a minute will suffer from blurring caused by the movement of planetary features as the planet spins on its axis. 

In practice, achieving a sharp focus on an image that is bouncing around your laptop screen like a demented ping-pong ball is a pretty tall order, and conditions have to be exceptional to get images that show much detail. This wasn’t one of those evenings, and indeed, I gave up at around 8.30 because the dew was dripping off of everything and was worried it would get into the electrics! 

Nevertheless, the individual processed image stacks showed up recognisable features when compared with the BAA’s Mars mapper…    

 

Mars at 19.30 compared to BAA map (click on image to enlarge)

My image shows a hint of the Martian phase at the time (97%) which is not shown on the Mars map above.

NGC 6960: The Western Veil Nebula...

NGC 6960 in HOO

Object: NGC 6960 
Type: Supernova remnant
Constellation: Cygnus
Distance: 1,470 light years
Date: September 23rd. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD
Subframes: 10 x 300s Ha, 10 x 300s OIII, no flats, no darks (hot pixel removal in Astroart).

Stellarium map showing location of field of view

Tucked under the eastern wing of Cygnus, NGC 6960 (also nicknamed the “Witches’ Broom”) is a remnant of a supernova that is believed to have occurred approximately   8,000 years ago.  It is part of a larger nebula covering nearly 3 degrees of sky, and which includes the Eastern Veil nebula NGC 6992-5.  The link to my earlier image of the other half of this nebula gives more information about the object.

The image above is an HOO composite. Both seeing and transparency were not good during the evening of September 21st. and the resultant sub-frames were rather noisy, a sure sign of high altitude haze. I was also too lazy to take more or longer ones, although I may revisit this object in the near future. After grappling with a series of objects with very weak OIII signal, at least that of NGC 6960 is reasonably strong and facilitates image processing.

NGC 7000: The North America Nebula...

NGC 7000/IC 5070 in H alpha

Objects: NGC 7000 (North America nebula), IC 5070 (Pelican Nebula)
Type: Emission nebulae
Constellation: Cygnus
Distance: 1,500 light years
Equipment: SX Pro 694, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: September 14th. 2020
Subframes: 6 x 300s Ha, no flats, no darks (hot pixel removal in Astroart).

Stellarium map showing field of view

On October 24, 1786, William Herschel, observing the area of sky around Deneb (the alpha star of the constellation Cygnus) from Slough, England, noted a “faint milky nebulosity scattered over this space, in some places pretty bright.” The most prominent region was catalogued by his son John Herschel on August 21, 1829. It was listed in the New General Catalogue as NGC 7000, where it is described as a "faint, most extremely large, diffuse nebulosity.” 

On December 12, 1890, the German astrophotographer Max Wolf noticed the characteristic shape of the eastern part of the nebula on a long-exposure photograph, and dubbed it the North America Nebula. In addition, in a paper of June 10, 1891 he described the region near that nebula as photographed on a 3 hour plate taken on June 1 of that year.  However, an accurate position of the Pelican Nebula had to wait until Sep 7, 1899, where the object was described by British astronomer Thomas Espin. 

In his study of nebulae on the Palomar Sky Survey plates in 1959, American astronomer Stewart Sharpless realised that the North America Nebula is part of the same interstellar cloud of ionised hydrogen as the Pelican Nebula, separated by a dark band of dust, and listed the two nebulae together in his second list of 313 bright nebulae as Sh2-117.  American astronomer Beverly T. Lynds catalogued the obscuring dust cloud as L935 in her 1962 compilation of dark nebulae. Dutch radio astronomer Gart Westerhout also detected the HII region Sh2-117 as a strong radio emitter, 3° across, and it appears as W80 in his 1958 catalogue of radio sources in the band of the Milky Way. 

One of the most famous bright nebulae in the heavens, the North America Nebula is shaped very much like its namesake. Despite its relative brightness, its large size and low surface brightness make it undetectable with the unaided eye except in very dark skies, and even then only by using special filters to increase the contrast of its line radiation. The North America and Pelican nebulae (IC 5070) are part of an approximately 100 light year-wide ionised hydrogen region. Their shapes and apparent separation are due to clouds of obscuring dust lying between us and them. 

What star or stars are responsible for heating the gas has long been unknown, but recently the 2MASS infrared telescope, concentrating on the area obscured by dust, has shown that there is a massive O-type star in the general area of the nebulae, which is the most likely source of their radiation. Estimates of the distance of the North America and Pelican nebulae vary considerably, ranging from as little as 1500 light years to as much as 2200 light years. 

The image above maps the hydrogen alpha emissions of the region.  This represents “first light” of my new wide-field imaging system, comprising of a Samyang F2 135mm focal length lens coupled to a Starlight Xpress SX PRO-694 camera.  This gives a 5 x 4 degree field of view. 

To carry the lens and camera, I refurbished my old Vixen GPDX mount, re-greasing it and carefully adjusting the RA and declination worm drives to try and eliminate the horrendous backlash that had always plagued it. I also (reluctantly) retired its old and increasingly unreliable Skysensor control unit, replacing it with a Skysensor EQ5 upgrade kit which allows me to control the mount via EQASCOM.

Although such a short focal length system probably doesn’t need auto-guiding, I had a spare guide camera and a Vixen 450mm focal length guide scope, so I thought I may as well use them. 

The set-up is intended to be a portable one, although I will be setting it up in the same position in my garden.  I Araldited three steel washers to the hard-standing where I would be setting up the tripod, and used the GPDX’s excellent polar-scope to polar align. 

It all seemed to work pretty well first time. PHD reckoned the polar alignment error was only around 1.5 arc-minutes, with an RMS guiding accuracy of around 0.6”, way better than needed (and better than my observatory Avalon mount!), so I think the mount refurb went pretty well. 

At the moment I am manually focussing the lens but at F2, it is extremely sensitive and I may need some engineered assistance.  Spacing between the lens and the CCD camera is also critical. Fortunately I managed to find an assembly of various adaptors that connected the lens to the camera via my old ATIK manual filter wheel that manage to land the Ha focus point exactly on the “infinity” point of the lens. 

Manual focussing required a deft touch but was relatively easy using the focus indicator on the Astroart camera control module. For starters, I shot 6 x 300 second exposures in Ha at F2 (via an old 12nm Ha Astronomik filter) and was very pleased with the sharpness and detail in the single subs. There was a small amount of flaring around the brighter stars that I attributed to the filter and some small distortion of the stars in one corner of the image field, but nothing disastrous. 

OIII flares around stars

Attempting to use an old Baader filter for OIII imaging was a complete washout however, as the flaring around all stars made the sub-frames unusable. That filter will have to be replaced, hence the mono image above. 

I used Starnet to remove the stars from the stacked Ha data as I found the snowstorm of the Milky Way to be distracting. This allowed some minor selective sharpening and stretching of the nebulosity, although the data was pretty good even though I only had 30 minutes-worth of subs.  I restored the stars by layering a “de-stretched” and slightly Gaussian-blurred version of the original stack over the Starnet version in “blend” lighten mode. 

References: 

1. https://apod.nasa.gov/apod/ap171201.html 

2. https://en.wikipedia.org/wiki/North_America_Nebula 

3. https://cseligman.com/text/atlas/ngc70.htm 

4. https://cseligman.com/text/atlas/ic50a.htm#ic5070

Sharpless 2-115: The Troll Nebula...

Sharpless 2-115

Object: Sh2-115 (containing star cluster Berkeley 90)
Type: Emission nebula with open cluster
Constellation: Cygnus
Distance: 7,500 light years

Date: September 13th/14th. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 12 x 600s Ha, 12 x 600s OIII (3x3 binned), flats, no darks (hot pixel removal in Astroart).

High overhead during early autumn evenings flies the constellation of Cygnus. The Milky Way forms a star-strewn backdrop to the celestial swan, where many deep-sky objects can be found. One such object is Sharpless 115, an emission nebula that can be found 2 degrees north-west of Deneb, the alpha star of Cygnus the Swan and easternmost star of the Summer Triangle.

Stellarium map showing location of field of view

Noted in his eponymous 1959 catalogue by astronomer Stewart Sharpless, this faint nebula lies along the edge of one of the outer Milky Way's giant molecular clouds, about 7,500 light-years away. Fluorescing with the light of ionized atoms of hydrogen, sulphur and oxygen, the nebulous glow is powered by hot stars in star cluster Berkeley 90 (the cluster of small stars just below left of centre in the field of view above). The cluster stars are thought to be only 100 million years old or so and are still partly embedded in its parent nebula. 

To the northwest of Sh-115 can be seen dim streaks of nebulosity catalogued as LBN 362 (the LBN designation referring to the Lynd’s Bright Nebula catalogue). Embedded within that is a small bright circular emission nebula given the designation SH2-116. This object was first classified as a planetary nebula (hence its alternative designations of Abell 71 or PK85+4.1) but recent studies show it to be an HII emission region instead. 

The evening of September 13^th offered good “seeing” (the air was steady) but less than perfect transparency. Hydrogen alpha data of this faint object showed up well, but was slightly blurred by what seemed to be very faint high-altitude haze. The stars were a little bloated, even though guiding and focus seemed good. Nevertheless, the miracle of Starnet allowed me to remove the stars from the image so that I could polish up the nebula (mild stretch, denoise, despeckle, unsharp mask) and then add the stars back in afterwards.

(I used a “destretched” version of the Ha stack that just showed the brighter stars, although I did paste in a bit of stretched stack to show up the Berkeley 90 cluster).

"Starnet" version of Ha data, stars restored

Needless to say, anything less than perfectly clear air hamstrings any attempt to gather OIII data on such weak sources such as Sh2-115.  Indeed, only a trace of signal could be found on 600 second exposures binned at 3x3. As a result, even a stack of 12 of such frames looked pretty awful. 

Raw OIII data stack

I ran this though Starnet and was surprised to find that it worked though, just leaving behind some of the more bloated stars that I could manually clean up. A combination of the 3x3 binning and weak signal still left a very grainy stack, so I applied a strong Gaussian blur (radius 5) to the starless frame before adding a star layer back (made from the original OIII stack, with brightness and contrast strongly adjusted to leave just the brightest stars, which were then Gaussian blurred, radius 2 to remove the binned “blockiness”) in “blend lighten” mode.

Final OIII stack

An HOO composite from the Ha (as red), OIII (as blue) and a 70/30 OIII/Ha blend was then used to give an RGB colour image, which I sharpened up a bit by adding the Ha data back over as a 50% luminance layer. At first I couldn’t turn a strong magenta hue in the nebula into the more pleasing OIII-related blues without getting weird colours elsewhere. Eventually, I took the OIII layer and pasted it over a blue background in “hard light” mode, that gave blue OIII nebulosity and white stars on a dark background. This got pasted over the colour frame in “dodge” mode at around 20%, which succeeded in bringing out the blue without overly affecting the rest of the colour balance.  

A bit of selective tweaking in curves gave the final colour image above, such as it is. 

After I put this post up, an acquaintance showed it to their astronomy-mad grand-daughter. She thought that the nebula looked like a troll, a horned and bearded beast who was trying to grab the Berkeley 90 cluster in two giant paws. 

I can see where she was coming from, hence the amended title of this post… 

Sh2-115 with extra added troll...

References: 

https://apod.nasa.gov/apod/ap130614.html 

http://www.astromaster.org/oggetti/sharpless_data/Sharpless_r.pdf 

https://jthommes.com/Astro/SH2-115_116.htm 

https://heasarc.gsfc.nasa.gov/db-perl/W3Browse/w3hdprods.pl

NGC 6820...

Ha/Ha/SII/OIII = LRGB

Object: NGC 6820, Sh2-86 (containing star cluster NGC 6823)
Type: Emission nebula with open cluster
Constellation: Vulpecula
Distance: 6,000 light years

Date: July 10th/11th, 18th/19th. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 16 x 600s Ha, 8 x 600s SII, OIII (2x2 binned) no flats/darks (hot pixel removal in Astroart).

Strictly speaking, NGC 6820 is a small reflection nebula near open cluster NGC 6823, discovered on August 7, 1864 by Albert Marth. The reflection nebula and cluster are embedded in a large faint emission nebula called Sh2-86, but the whole area of nebulosity is usually referred to as NGC 6820. Cluster NGC 6823 was discovered on July 17, 1785 by William Herschel

Map showing approximate image field of view

The rather obscure constellation of Vulpecula lies overhead during UK summer evenings, bounded within the three bright stars of Deneb, Vega and Altair, together called the "Summer Triangle". The whole area is rich in deep sky objects, lying as it does on the plane of the Milky Way, which itself can be glimpsed as a faint hazy band of light on those rare clear summer evenings. Vulpecula itself, although small, contains several objects of note, including M27, the Dumbbell Nebula.

Open star cluster NGC 6823 is about 50 light years across and lies about 6000 light years away. The centre of the cluster formed about two million years ago and is dominated in brightness by a host of bright young blue stars packed in a Trapezium-formed region about 1.3 x 0.7 light-years across. Outer parts of the cluster contain even younger stars. It forms the core of the Vulpecula OB1 stellar association.

The most striking feature in the image above is the trunk-like pillar of dust and gas protruding from the eastern side of the nebula towards the adjacent star cluster. The huge pillars of gas and dust are formed by surrounding gas and dust being pushed and eroded away by stellar winds and radiation from the brightest cluster stars. Dark globules of gas and dust (Bok globules) are also visible in the nebula.

Bok globules, named after the Dutch astronomer Bart Bok (who proposed their existence in the 1940′s) are dark clouds of dense cosmic dust and gas within star-forming regions in which usually star formation takes place. They most commonly result in the formation of double or multiple star systems.

I nearly didn’t bother processing the Ha data. The seeing on the night of July 10^th/11^th was terrible, and it was very hard to get a sharp focus on a star. The nebula itself also wasn’t as bright as I thought it might be and so retrospectively, 600 second unbinned exposures against a less-than-dark summer sky was perhaps rather optimistic. Sure enough, the nebula itself was faint and rather fuzzy due to poor focus and required a hefty stretch such that the result was overwhelmed by bloated stars (see below)...

Original Ha stack, with bloated stars

Just as an experiment, I decided to run the above image through Starnet, a piece of freeware that has the ability to remove stars from images of nebulae. I was rather surprised and pleased with the result (below).

Starnet rendition of stretched Ha stack...

I think that completely starless images of nebulae do look a bit weird however, so I blended it with an unstretched copy of the original stack that just more or less showed stars. The lack of stretching meant the starts hadn’t blown out and after a mild Gaussian blur (0.8, just to avoid a “painted-in” look), I dropped the star layer back onto the starless version in PSP "lighten" mode to produce what became the luminance/red channel (see image below).

NGC 6820 (Hydrogen alpha only)...

I finally got the SII and OIII subframes (600s binned) last nightin between a few clouds (18th/19th July) that enabled me to complete a colour rendition of this object. Colour RGB image was produced in Astroart (red - Ha, green - SII, blue - OIII) and finished in PSP, layering the Ha stack back over the RGB image as a luminance layer as the OIII/SII stars were a bit blown out. There wasn't much in the way of SII data at all, just a sort of general glow in the central area of the nebula.

References:

https://en.wikipedia.org/wiki/NGC_6820_and_NGC_6823

http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/ngc-6820-6823-by-robert-gendler/

https://cseligman.com/text/atlas/ngc68.htm#6820

Comet C/2020 F3 (NEOWISE)...

Object: Comet C/2020 F3 (NEOWISE)
Type: Comet
Constellation: Lynx
Distance: 134 million miles

Date: July 11th. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount

Subframes: 10 x 60s and 3 x 120 sec each for luminance and RGB, stacked and colour combined in Astroart, final processing in PaintShop Pro

It was with faint optimism that I swung the telescope down to this target at the end of a long imaging session. Initially the scope was pointing at a hedge, but the comet soon cleared my local obstacles and starting at around 3 a.m, I rattled off some exposures before the comet was quickly drowned out by the brightening dawn twilight.

Mk1 NEOWISE image...

The subs were messy (to say the least!), full of weird gradients and blobs brought on by the rapidly changing twilight conditions and some local horizon objects crossing the field as the telescope tracked the comet.

I processed the one minute frames to give (after a lot of work) a cleanish image, but still plagued with psychedelic background colours (see opposite). I was going to leave it at that, but today I thought I'd layer in the sky background from my first image of this comet, plus some data from the 120 second subs which showed a hint of the blue ion tail. The eventual result is the main image above, which I'm rather pleased with...

This comet is probably the most striking since Hale-Bopp back in 1997. Recent infra-red studies show that NEOWISE's nucleus is quite large, at around 5 km in diameter, hence its brightness. Hopefully it will remain as bright as it moves into the south-western evening sky (at a more civilised time!) over the course of the next few weeks...

Moon...

Waxing gibbous Moon...

Object: Moon (77% of full)
Constellation: Aquarius
Distance: 399523 km (248252 miles)

Dates: 11th. July 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount
Subframes: 100 x  H-alpha (0.001s)

From the same session as the previous image, this one also nearly didn't make it on screen. I thought I'd grab a few subs of the moon as an afterthought, so I just slewed the telescope from my previous target (NGC 6820) down to the moon, which was lurking low down in the sky at about 16 degrees above the south-eastern horizon.

I made the mistake of not checking the focus before acquiring the subframes, and no amount of messing around in Registax or PaintShop will ever get back that missing detail...

I've put the final image up anyway, if only as a reminder of my own carelessness.

Comet C/2020 F3 (NEOWISE)...

Comet NEOWISE...

Object: Comet C/2020 F3 (NEOWISE)
Type: Comet
Constellation: Auriga
Distance: 160 million miles

Date: July 6th. 2020
Equipment: Canon 450D, Vixen 600mm 114 ED refractor, GPDX mount

Subframes: 34 x 1 sec @ ISO400,  processed in Registax.

Comet C/2020 F3 NEOWISE’s unusual name comes from NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), which discovered the comet on March 27, 2020.  It is a retrograde comet with a near-parabolic orbit.  It survived its closest approach to the Sun on July 3, 2020 at perihelion 0.29 AU (43 million km) from the Sun, some 14 million km closer on average than the planet Mercury, an encounter that causes many comets to disintegrate.  Solar heating of this ball of ice and rock subjected it to temperatures of nearly 600C, causing it to dramatically brighten and shed gas and dust, giving rise to a cometary tail.  

My image above gives a fair representation of what the comet looks like through 6 x 30 binoculars before the dawn twilight gets too bright. 

Closest approach to Earth will occur 23 July 2020 at a distance of 0.69 AU (103 million km). This perihelion passage will increase the comet's orbital period from about 4500 years to about 6800 years.

Originally, NEOWISE was not expected to get much brighter than ninth or 10th magnitude, making it accessible only to those with good binoculars or small telescopes. During the spring, observers in the Southern Hemisphere followed the very rapid brightening of this object as its distances from both the sun and Earth decreased.  A consensus of observations placed it at magnitude +9.9 on May 10. Just under a month later, on June 7, the comet was on the far side of the sun, 73 million miles (117 million km) distant from the star and 147 million miles (236 million km) from Earth. It had increased 12-fold in brightness to a magnitude +7.2. As projected on the sky, the comet was scarcely 24 degrees from the sun (a closed fist at the end of an outstretched arm covers 10 degrees of the sky) and the two were rapidly closing together. Shortly thereafter, the comet was lost to earth-based observers in the increasing glare of the sun.

From June 22 through to June 27 however, the comet was within the range of the Solar and Heliospheric Observatory (SOHO). SOHO is a cooperative mission between the European Space Agency (ESA) and NASA. The spacecraft is stationed in a halo orbit around the sun-Earth L1 Lagrangian point, a position roughly 930,000 miles (1.5 million km) sunward of Earth. At this point in space, the orbital period of SOHO exactly matches the orbital period of Earth. From this orbit, SOHO is able to observe the sun 24 hours a day.

Using its Large Angle and Spectrometric Coronagraph (LASCO-3, which uses an occulting disc to block out the glare of the sun's disc from its images), NEOWISE could be monitored as it passed near to the sun.  During this time, the comet appeared to significantly brighten, just before it passed out of the field of the LASCO-3 camera. Comet NEOWISE also appeared to have developed a rather bright, albeit short and stubby forked-shaped dust tail.

Comets fall into two categories. "Common" comets are faint fuzz-balls that are visible only with the help of good binoculars or telescopes. At any time there may be perhaps eight or 10 such comets in our sky. Then there are the "Great" Comets, those that become bright enough to be plainly visible with the naked eye and accompanied by a striking tail of dust and gas. Unfortunately, such objects do not come around very often. In the average human lifespan, you may get a chance to see perhaps four if you are very fortunate.

The last great comet visible from the Northern Hemisphere was Comet Hale-Bopp in 1997, but is NEOWISE developing into one right now? Based on the very latest brightness estimates, Comet NEOWISE might fall just short of the criteria, though once it becomes evident in darker skies it should be quite obvious, especially away from light polluted cities.

Catching this comet required an early morning start, to see it emerge above the horizon for about 40 minutes before the glare of the rising Sun drowns it out.  At 3.45 a.m. the comet was a mere 8 degrees above the horizon and had just got above the roof of my next door neighbour's house.

Position of Comet NEOWISE on the morning of July 6th. 2020

The chart opposite shows its position in the sky that morning.

I was able to rattle off about 40 exposures, with one second ISO 400 exposures seeming to offer the best contrast between the comet and the rapidly brightening morning sky. The comet, with just a hint of its tail, was just visible to the naked eye in the morning twilight, but only because I knew exactly where to look, thanks to a laptop looking after the telescope pointing!  Through small binoculars, the tail was very evident and the jets on either side of the comet head could be seen.

I estimated its magnitude to be around 2, though its low elevation in the morning twilight makes such assessments difficult. It is certainly the brightest comet I have seen in the UK since Comet 17P Holmes back in October 2009.

Over the next few weeks, the comet draws away from the Sun, becoming an early evening object towards the end of July (see chart below).  It will be interesting to see if NEOWISE continues to remain bright as it passes by the Earth.

Track of Comet NEOWISE during July in 2020.

References:

1)  https://en.wikipedia.org/wiki/C/2020_F3_(NEOWISE)

2)  https://www.space.com/comet-neowise-july-2020-night-sky-forecast.html

Messier 16: The Eagle Nebula...

M16: the Eagle Nebula...

Object: Messier 16 (NGC 6611: nebula catalogued as IC 4703, Sh2-49)
Type: Open cluster with nebula
Constellation: Serpens Cauda
Distance: 6,000 light years

Date: June 22nd. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 12 x 300s Ha, 12 x 300s + 6 x 300s (2x2 binned) OIII, no flats/darks (hot pixel removal in Astroart).

The sixteenth entry in Charles Messier’s famous catalogue of deep sky objects has a long and interesting history. The star cluster itself was first discovered by Swiss astronomer Jean-Philippe de Cheseaux in 1745–46, and was subsequently “rediscovered” on June 3, 1764 by Messier (who listed it as M16 in his own catalogue).

Messier described M16 as a “cluster of faint stars mingled with faint luminosity” although it is not clear that he actually observed the nebula itself, as Messier often accredited star clusters with nebulosity (a product of the poor quality of his telescopes rather than his undoubted ability as an observer).

French astronomer Etienne Trouvelot subsequently observed the nebula and described it in detail (nicknaming it “the Fan”) prior to British astronomer Issac Roberts photographing it in 1894. 

For the IC catalogue, John Dreyer treated M16 as being primarily the cluster itself, listed it as NGC 6611, and added the IC entry for the nebula lit by the cluster.

M16 has had various popular monikers, but the “Eagle nebula” seems to have stuck (although I think Trouvelot’s name is the most sensible). The occasionally-used "Star Queen Nebula" was introduced by Robert Burnham, Jr., in his lyrical description of the object in his classic Celestial Handbook, reflecting his characterization of the central pillar as the "Star Queen", shown in silhouette. 

Location of image field, looking south on June 22nd

Messier 16 can be found in the constellation of Serpens Cauda, low in the southern mid-Summer sky from UK latitudes (see map opposite) where, on rare evenings, the faint glow of the centre of our Milky Way can be glimpsed. M16 is best seen visually in a low-powered, wide field telescope. 4-inch instruments will resolve about 20 stars against several regions of faint nebulosity. The brightest portion of the nebula (which I imaged back in 2006) spans about 20 arc-seconds (a bit less than the diameter of the full moon) although my latest image above shows that it is just the brightest part of a whole expanse of faint nebulosity lurking in the distant Sagittarius arm of our galaxy.

Unfortunately, the general public’s expectations of night sky observing have been raised by the Hubble Space telescope and its iconic images of the Pillars of Creation, and folk are often disappointed by the faint, monochromatic real life views of nebulae such as M16 through amateur telescopes

The pillared, dust-strewn heart of M16 is a stellar nursery, where stars are being born inside dense clouds of cold gas. The detailed Hubble images of several of these natal cocoons led to their naming as the “Pillars of Creation”. The images show these clouds bathed in intense ultraviolet light from M16’s cluster of young, massive stars, with jets of gas streaming off the pillars as the intense radiation heats and evaporates it into space. Denser regions of the pillars are shielding material beneath them from the powerful radiation.

Imaging from the Medway valley with a 4-inch refractor, one is at a slight disadvantage compared to the Hubble telescope. Instead of the vacuum of space, my telescope is attempting to peer through a haze of dust and light-polluted air, particularly as M16 never rises greater than 25 degrees above my southern horizon.  Also, at this time of year, the sky has no true astronomical darkness as the sun never sets more than about 14 degrees below the horizon, although to me the sky looked as dark as it ever does when I started out taking sub-frames at around 23.30 on a warm summer’s evening. 

Auto-guiding wasn’t brilliant given that I was trying to image through warm air low in the sky, but it was good enough.  The Ha data was reasonable and given that I only had about 3 hours of darkness to play with, I swapped over to gathering some OIII frames after I had a dozen Ha frames in the electronic bag. 

Whilst the true colour of deep sky celestial objects is a fairly subjective thing, I am no fan of the “Hubble pallet”, a colour scheme used by NASA to render its images (and which as a result is now fashionable with amateur astro-imagers) whereby H-alpha light is assigned to the green channel and S-II to the red, with OIII as the blue. 

To me, hydrogen emission nebulae should be red, not lurid psychedelic yellows, greens or blues.  However, the plethora of such images of M16 led me to expect a much stronger OIII signal than I was actually getting. Fortunately, I had logged on to Stargazers Lounge and was able to ask the question, with veteran astro-imager Carole Pope suggesting that I take 2x2 “binned” exposures (where four adjacent pixels are bulked together to act as one on the camera chip, increasing sensitivity and reducing background “noise”). I don’t like the way this sometimes makes smaller stars a bit blocky, but it seemed to work OK this time and I was able to grab a few brighter images before an owl sat on my telescope (I think!).

Earlier, when I walked down the garden slope to my observatory to set up, a barn owl had swooped just in front of me, a white flash in my head-torch light that had startled me no end.  I have been visited by the local tawny owls in the past and indeed, one had once flown into the open dome hatch while I was in the observatory, giving me another late-night heart attack experience.

On this occasion, I was keeping an eye on the equipment remotely via a Cat 6 cable link from the observatory lap-top to another indoors. Suddenly, the auto-guiding graph shot off-scale and I thought “cable snag”. I dashed down to the observatory, where everything fortunately seemed normal, although the target was now off-centre. Looking around though, there were a couple of pale feathers on the floor (no other “debris”, luckily…) and I suspect I may have had another avian intruder. Whether the faint light of various LEDs or the gentle ticking of the mount tracking motors attracts them, I don’t know, but I decided to quit while I was ahead. By this time, it was around 3.00 am and the sky was starting to brighten anyway.

It was nice to see Jupiter and Saturn, low together towards the south in the peaceful darkness, with the bright baleful orange of Mars rising over my south-eastern horizon. I toyed with the idea of dragging my C9.25 out for a closer look but thought better of it, and went to bed instead. I am getting old.

Hubble image compared with centre crop from main image, showing "The Pillars of Creation"...

I colour-combined the separate Ha and OIII stacks in both PaintShop Pro and Astroart (with Ha as RED and OIII as blue, with a 60:40 blend of OIII and Ha as a green channel), and got two strikingly different results. The AA version was very red, the PSP a more subdued orange. In the end, I settled for a blend of the two that you see here.

For amusement, I thought it would be interesting to compare the detail in the Hubble image to that obtained by my more modest set-up (see above). Whilst I think it is possible to tell which is which, I was surprised to find that most of the prominent features can be found in my version.

Update:

There is a bit of freeware kicking around on the internet called Starnet. It uses a clever algorithm to rub out stars from astropics.  I hadn't had much luck with getting it to work until my son came home from university and managed to run it on his computer.

Here's what M16 looks like without stars...

Not sure if I like it. It looks like a Turner painting. It does open up possibilities for image processing as you can mess around with selectively processing areas of the image without messing up stars, which can be added back in afterwards. 

Moonrise over Wouldham Common...

 

Moonrise...

Taken this evening using my nifty and rather under-used Celestron C4SE Mak afocally coupled to a Canon 450D.  Combination of 1/800s exposure for the moon and 1/8 s exposure for the background, layered in PaintShop Pro.

Messier 3...

Object: Messier 3 (NGC 5272)
Type: Globular cluster
Constellation: Coma Bereneces
Distance: 34,000 light years

Date: April 25th 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 20 x 150s (2x2 binned) each for RGB, flats for each channel, bias as darks (hot pixel removal in Astroart).

Globular clusters are some of the oldest objects in the universe. They consist of vast, spherical agglomerations of stars, typically hundreds of thousands in number, and exist in galactic halos in orbit around larger galaxies.  The Milky Way galaxy has around 150 globular clusters in attendance, with more massive galaxies having proportionally larger numbers.

M3 was discovered on May 3, 1764, and was the first object in the Messier catalogue to be discovered by Charles Messier himself. Messier originally mistook the object for a “nebula without stars”. With a larger and better quality telescope, the object was resolved into stars by William Herschel around 1784, who first coined the term “globular cluster”.

Stellarium map showing location of image field

From the UK, M3 can be found high above the southern horizon at around midnight in late April, between the bright stars Arcturus and Cor Caroli. The cluster has a bright core with a diameter of about 6 arcminutes and spans a total of 12 arcminutes (or just under the half the diameter of a full moon). This cluster is one of the largest and brightest of its type, and is made up of around 500,000 stars. It is estimated to be 11.4 billion years old.

I had originally planned to gather both luminance and colour data for this object, but the seeing was very poor and I struggled to get the auto-guiding to run below 1.3” RMS, so I restricted myself to collecting 2x2 binned sub-frames, where the guiding requirements aren’t as demanding.

However, I was quite pleased with the way the RGB image scrubbing up without any additional luminance data, so I’ve decided to let well enough be. 

If you look closely, the image shows up the strange straight lines of stars that appear to run from the edges of the cluster, which Stephen O'Meara illustrated for M3 in his book "Deep-Sky Companions - The Messier Objects".  It also shows up the 16th magnitude spiral galaxy NGC 5263, visible at the centre right of the main image as small fuzzy dash of light and lying some 196 million light years away...