Comet C/2022 E3 (ZTF)...

Comet C/2022 E3 (ZTF)...

Object: Comet C/2022 E3 (ZTF)
Type: Comet
Constellation: Ursa Minor
Distance: 48.9 million miles (at 20.15, Jan 27th 2023)
Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD

Date: January 27th. 2023.
Subframes: 18 x 200s each for LRGB (comet): 6 x 20s each RGB for stars, flats, bias as dark frames.

Astronomers discovered Comet C/2022 E3 (ZTF) using the 48-inch (1.2-meter) Samuel Oschin robotic telescope (part of the Zwicky Transient Facility (ZTF), located at Mt. Palomar in southern California). Once confirmed as a comet, the standard naming convention for it was adopted: it was the 3rd such object discovered in the fifth half-month (A, B, C, D, E) of the year, hence the label 2022 E3 (ZTF).

Comet C/2022 E3 (ZTF) was in the morning sky, in the direction of the constellation Aquila when astronomers with the Zwicky Transient Facility first spotted it.

The ZTF program images the whole Northern Hemisphere every two nights looking for supernovae, variable stars, binary stars, flashing merging neutron stars, asteroids and comets. Overall, it has discovered 10 comets in the past three years.

When astronomers first detected C/2022 E3 in March 2022, the comet was around 400 million miles from the sun, or just within the orbit of Jupiter. At that time the comet was a very faint 17th magnitude, initially appearing as a stellar object until its proper motion showed it moving against the sky background.

The solid, core structure of a comet is known as the nucleus. Cometary nuclei may be up to 20 miles across (Hale-Bopp was one such monster) but are generally much smaller: the nucleus of Comet C/2022 E3 (ZTF) has been estimated to be only a mile across. Because of their low mass, comet nuclei do not become spherical under their own gravity and often have irregular shapes.

Cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. As such, they have been popularly described as "dirty snowballs". The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick. In addition to the gases already mentioned, the nuclei contain a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde, ethanol, ethane, and other, more complex molecules such as long-chain hydrocarbons and amino acids.

These nuclei normally orbit the Sun at an immense distance right on the very edge of the Solar System as part of a sphere of such objects surrounding it, known as the Oort Cloud, Occasionally, one such nucleus will undergo a gravitational encounter, perhaps with the distant giant planet Neptune, one that will send it spiralling in towards the Sun.

As the frozen nucleus approaches the Sun, solar radiation increasingly releases a huge and extremely thin atmosphere around the comet called the "coma". It is this coma that we see, rather than the nucleus of the comet itself. The force exerted on the coma by the Sun's radiation pressure and solar wind cause a cometary "tail" to form pointing away from the Sun. Both the coma and tail are illuminated by the Sun and start to become visible when a comet passes into the inner Solar System. Cometary dust reflects sunlight directly while the gases glow from ionisation by the Sun's intense radiation.

It was it this point that the researchers made out the distinct tail, or coma, proving that C/2022 E3 (ZTF) was indeed a comet rather than an asteroid.

The green colour of Comet C/2022 E3 (ZTF) is typical of comets and is believed to be due to the presence of an unstable form of carbon molecule (“dicarbon”) formed by the photolysis of the carbon compounds present in the nucleus, and which fluoresce with a green light under solar irradiation in the vacuum of space.

Occasionally a comet may experience a huge and sudden outburst of gas and dust, during which the size of the coma greatly increases for a period of time. This happened in 2007 to Comet 17P Holmes.

The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet's orbit in such a manner that it often forms a curved tail called the type II or dust tail.  At the same time, the ion or type I tail, made of gases, always points directly away from the Sun because this gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory.  On occasions - such as when Earth passes through a comet's orbital plane, an “anti-tail”, pointing in the opposite direction to the ion and dust tails, may be seen.  This has been observed for Comet C/2022 E3 (ZTF) and can be seen in my image.

By Jan. 12, 2023, the comet had travelled nearly another 300 million closer to Earth, becoming visible in the night sky near the northern constellation Corona Borealis. As stated earlier, solar radiation ionises the gas emitted from the comet, giving rise to complex magnetic fields around it. While making its closest approach to the Sun, a blast of radiation and solar particles (called a “coronal mass ejection”) swept over the comet, squeezing its magnetic field lines together and leading to a disruption in the flow of gas from the comet – a "tail disconnection event" which was clearly observed from Earth.

On February 1 and 2, Comet C/2022 E3 (ZTF) will have reached its closest point to Earth (27 million miles) and can be seen overhead against the background of the rather obscure constellation of Camelopardalis, close to the borders of the better-known constellations Ursa Major and Ursa Minor. A map of the comet's progress is shown below:

Track of comet C/2022 E3 (ZTF) during February 2023...

A few days later, on Feb. 5 and 6, the comet will pass across the night sky to the west of the bright star Capella and then pass across the constellation Auriga. On Feb. 11th, it lies just to the east of Mars. From there, it will descend toward Taurus, becoming ever dimmer as it moves away from Earth, back out toward the edge of the solar system. 

The last time Comet C/2022 E3 (ZTF) passed near the sun was 50,000 years ago. However, the latest orbital element calculations suggest that the comet’s recent close approach to the Sun has changed its orbital path to a parabolic orbit, rather than an elliptical one. Such an orbit is not “closed”, so after it sweeps around the sun C/2022 E3 will move back out into deep space, never to return again.

Much blather has been written by the excitable English press (particularly the Daily Mail) about poor old Comet C/2022 E3 (ZTF), with headlines hyping it up to be an eyeball-searing, “one-in-a-lifetime event”. The truth, on the odd occasion that it can ever be found, is much often more mundane and is usually buried in the depths of the article. I can, however, reassure you that the comet will not affect house prices, cause cancer or lead to a rapprochement with the EU, whatever the Daily Mail may say in future.

The reality is that bright comets — the kind that can be seen easily without binoculars or telescopes — appear on average perhaps two or three times every 15 to 20 years. The last such comet to do that was Comet NEOWISE (C/2020 F3) in July 2020 – hardly a “once-in-a-lifetime” event.

Then there are the common comets, of which most are only visible either with good binoculars or a telescope. If you look at my blog (both old and new) indexes, you will find several examples of ones I have imaged over the years.

The vast majority of comets fall into this category, but C/2022 E3 (ZTF) may end up ranking as “slightly brighter than common”, since for a short while it may hover at around “fifth magnitude”, the limit of naked-eye visibility (and only for those fortunate enough to be blessed with dark, non-light polluted night skies). Additionally, the light from a comet is not a bright point, but a fuzzy, diffuse spot, one that will be increasingly difficult to pick up from a night sky containing a bright waxing moon that will be full on February 5^th.

I was able to pick up the comet in 7x50 binoculars as a tiny fuzzy blob, but only because I knew exactly where to look (and I am also a fairly experienced night-sky observer armed with a computer-controlled camera set-up that was pointing the way!)

My image shows the comet displaying a distinct greenish colour and sprouting two faint tails, the gas tail being the long one to the right on the image. Sadly, such long-exposure images tend to be quite deceptive. For one thing they bring out colours and levels of detail that are not readily evident to the eye, even through binoculars or telescopes.

My CCD camera is a monochrome device, which is more sensitive than colour cameras. To get colour data, I have to take multiple exposures through colour filters. This works just fine with most celestial objects, which don’t move against the sky background.

Comet C/2022 E3 (ZTF) was “motoring” in celestial terms against the background sky, however. My set-up was able to “guide” the camera, locking it on to the comet, but this meant that the stars became trailed on the long cumulative exposures as the comet was moving quite perceptibly across the sky background. You will see the stars as faint grey (luminance), red, green then blue lines on the above image as the filters were placed in sequence during the imaging session.  

To capture stars for the image that allow a frame of positional reference, I just shot a few short exposures with the camera guiding on a star as usual. Combining the separate LRGB exposures together gave the colour image of the comet, with the stars overlaid in “screen mode” to give the view you see above.

"Starless" monochrome version....

Just as an experiment, I ran the individual luminance sub-frames through Starnet and then stacked them. Although a bit noisy, the cometary tails do seem to stand out a bit better, with the "fan" of the dust tail spread out across the comet's orbital plane and the twin tail gas clearly visible off to the right.

IC 410 and IC 405: Tadpoles and the Flaming Star...

IC 410 and IC 405...

Object(s): IC 410 and IC 405
Type: Emission nebulae
Constellation: Auriga
Distance: 12,000 light years (IC 410) and 1500 light years (IC 405)
Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: January 21st. 2023
Subframes: 18 x 300s each for Ha (1x1 binned) and OIII (2x2 binned), 12 x 200s (2x2 binned) for RGB: flats, bias as dark frames.

Location of the field of view in the night sky...

This particular area of the Orion Milky Way, beneath the constellation of Auriga, offers a rich zone of targets for any astrophotographer.  It is an area that I have visited several times before, but the 5 degree field of the Samyang f2 lens offers a chance to place many targets in the same field of view, to show their proximity to each other.

At the top left of the field of view lie the two open clusters, M38 and NGC 1907. I imaged these back in 2010: these clusters lie at around 4500 light years away, in between IC 410 and IC 405. 

Below these clusters lie "The Spider and the Fly", IC 417 and NGC 1931. I imaged these nearly three years ago . 

Discovered by Max Wolf on September 25th 1892, IC 417 ("the Spider") is a star cluster with an associated emission nebula, and lies about 7500 light years away. A wider area of hydrogen alpha emission extends from it and is classified as Sharpless 2-234. The smaller but brighter NGC 1931 was discovered by William Herschel on February 4th 1793, and is also an emission nebula with an associated cluster, as well as an element of reflection nebula. It, too, has a Sharpless designation (Sh2-237) and lies at a similar distance to IC 417.

Designations of the objects in the image field of view...

IC 410 is very much a background object, lying over 12,000 light years away. It is often called the "Tadpoles" nebula, after the two blobs of star-forming dust and gas within it, designated as Simeis 129 and 130 respectively, and which just about show up on the main wide field image above. I pictured these back in January 2019. The nebula IC 410 was discovered by Max Wolf on September 25th. 1892, and strictly speaking the IC 410 designation refers to the brightest area of nebulosity surrounding open cluster NGC 1983, an earlier John Herschel discovery from January 22nd 1827. These days, IC 410 is taken to be the entire nebula, which also has the Sharpless designation Sh2-236.

IC 405 (also designated Caldwell 31 by Sir Patrick Moore in his own catalogue of deep sky objects) is the "Flaming Star" nebula, which I pictured back in December 2019.  It was discovered on March 21st. 1892 by John Schaeberle. IC 405 also has a wider area of H-alpha nebulosity associated with it, designated as Sh2-229, although they all tend to be regarded as "IC 405" these days. At a mere 1,500 light year distant, it is a foreground object compared to the others in this field of view.

The whole area is designated as Sharpless 2-230.  I did take a wide field image of Sh2-230 back in January 2009, but since then both my equipment, software and processing techniques have improved (though the mount is still the same!)

In terms of processing, the biggest problem is that the nebulae are overwhelmed by a blizzard of the Milky Way stars. The magic of the "Starnet" software was used to "de-star" the various narrowband and colour image stacks, allowing me to replace just the brighter stars and clusters back into the image at a more visually aesthetic level.

Messier 45: The Pleiades...

Messier 45: The Pleiades...

Object: Messier 45
Type: Open cluster with reflection nebula
Constellation: Taurus
Distance: 440 light years
Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: January 8th. 2023
Subframes: 12 x 300s each for LRGB, flats, bias as dark frames.

Set high in the winter sky as part of Orion’s glittering retinue, the Pleiades have certainly been known to Man ever since prehistoric times, ever since the first glimmerings of human intelligence compelled our ancestors to look upwards to the night sky in awe and wonder.

At a distance of about 440 light years, the Pleiades is one of the nearest star clusters to Earth. It is certainly the nearest Messier object to Earth, and is the most obvious star cluster to the naked eye in the night sky.

Location of image field of view in the night sky...

In Greek mythology, the Pleiades were the seven daughters of the Titan, Atlas, who was condemned by Zeus to forever bear the weight of the heavens as punishment for rebelling against the Olympian gods. Without their father to protect them, the Pleiades attracted the amorous attentions of the nearby hunter, Orion, and so to save them, Zeus transformed them into the stars we see today. Atlas and his wife, Pleione, also became part of the starry retinue of the Pleiades: “Pleiades” means “the daughters of Pleione”, and Mum and Dad keep watch over their daughters as the two stars closely adjacent stars on the eastern side of the cluster.

The Pleiades have been traditionally known as a group of seven stars. In various Greek and Roman writings, they are referred to as The Starry Seven, The Seven Virgins or the Seven Atlantic Sisters. These ancient descriptions come from days long before the advent of telescopes or binoculars, yet today, only six Pleiads are easily visible to the unaided eye. This state of affairs is supported by modern measurements of the brightness of the stars of the Pleiades. Only six of them are above “fifth magnitude”, the accepted threshold for naked eye visibility.

Magnitudes of the nine brightest members of the Pleiades are shown in the greyscale image below:

Magnitudes of the nine brightest Pleiads...

With an apparent magnitude of +2.85, the brightest star in the cluster is Alcyone, a blue-white B-type giant, similar in type to the other bright B-type stars in the Pleiades cluster. Alcyone has a mass of 6 times that of the Sun, and an effective radius of almost ten times that of the Sun, but the actual radius is lesser at poles and greater at the equator due to its high rotational velocity, which causes it to have an ellipsoidal shape. Its temperature is approximately 12,300 K (over twice as hot as our Sun) with the actual temperature being greater at the poles and lesser at the equator. Its luminosity is 2,030 times that of the Sun.

The light of the cluster is dominated by hot blue luminous stars that have formed comparatively recently in astronomical terms. Ages for star clusters can be estimated by comparing the Hertzsprung–Russell diagram for the cluster with theoretical models of stellar evolution and using this technique, ages for the Pleiades of between 75 and 150 million years have been estimated.

One of the oldest traditions concerning the cluster is the persistent myth of a “lost Pleiad”. The Greeks identified her as Electra, who is said to have veiled her face at the burning of Troy. Another story casts Merope in the role, as she reputedly hid her face in shame at having married a mortal, the King of Corinth, while all her other sisters were wedded to gods.

The Greek poet Aratus (310-240 BC) refers to the tradition of the “Lost Pleiad” when he wrote:

“…Their number seven, though the myths oft say
And poets feign, that one has passed away…”

This tradition is not confined to Greek mythology. The story of a lost Pleiad also appears in Japanese lore: the cluster is mentioned under the name Mutsuraboshi ("six stars") in the 8th-century Kojiki (an early Japanese chronicle dating from the early 8th century), and is now known as Subaru. A similar theme figures in the legends of Australian aborigines, natives of the Gold Coast of Africa and the head-hunters of Borneo:

“Their Sister Stars that were once seven
Mourn for their missing mate in Heaven…”

It seems that the legend of the lost Pleiad may have a basis in fact, however. Those modern brightness measurements have revealed that the mythical mother of the Pleiades, Pleione, is variable in brightness by at least half a magnitude, and may well once have been above the threshold of naked eye visibility.

Galileo was the first astronomer to view the Pleiades through a telescope. He discovered that the cluster contains many stars too dim to be seen with the naked eye. He published his observations, including a sketch of the Pleiades showing 36 stars, in his treatise Sidereus Nuncius in March 1610.

Today, we know that the cluster is about 80 light-years across and contains over 1,000 statistically confirmed members, a figure that excludes an unresolved number of binary stars, which make up over 50% of the total stars in the cluster.

Curiously, the 11^th century Talmud (the central text of Rabbinic Judaism) uses the term kimah to describe the number of stars in the Pleiades, a word which means “over one hundred”.

Another thing revealed by long exposure photography is that the Pleiades are veiled in fine, dense threads of nebulosity, like cirrus clouds or interstellar cobwebs. It is questionable whether these are truly visible to the naked eye today, yet some translations of the biblical Book of Job refer to the “Chains of the Pleiades”. The seventh century Arabian poet Amr al Kais also hints at the nebulosity:

“The hour when the Pleiades appeared in the firmament
Like the folds of a silken sash variously decked with gems…

Perhaps the most famous reference to the Pleiades nebulosity in English literature occurs in Tennyson’s Locksley Hall…

“Many a night from yonder ivied casement, ere I went to rest
Did I look on great Orion, sloping slowly to the west
Many a night I saw the Pleiads, rising thro’ the mellow shade
Glitter like a swarm of fireflies tangled in a silver braid…”

Charles Messier measured the position of the cluster and included it as M45 in his catalogue of comet-like objects, published in 1771. Messier's inclusion of the Pleiades has been noted as curious, as most of Messier's objects were much fainter and more easily confused with comets. The brightest area of nebulosity (called “Tempel’s Nebula) lies to the south of Merope does indeed look comet-like in appearance, however, so perhaps that is why Messier included the Pleiades in his famous catalogue.

These reflection nebulae can clearly be seen in the main image above, and more detailed photographs of the area show a mass of fine filaments that glitter with reflected starlight.

They are included in the 1966 catalogue of reflection nebulae compiled by Sidney van den Bergh, and are shown marked on the grey scale image below:

van den Burgh reflection nebulae in the Pleiades...

This dust was once thought to be left over material from the cluster star formation, but is now considered likely to be an unrelated dust cloud in the interstellar medium through which the stars are currently passing. The dust cloud is estimated to be moving at a speed of approximately 18 km/s relative to the stars in the cluster.  

The long exposures used in this image show up the interstellar dust around the Pleiades as a brownish cloudy background.

The total mass contained in the cluster is estimated to be about 800 solar masses and is dominated by fainter and redder stars, although its visible light is dominated by young, hot blue stars. The cluster contains many brown dwarfs, which are objects with less than about 8% of the Sun's mass, not heavy enough for nuclear fusion reactions to start in their cores and become proper stars. They may constitute up to 25% of the total population of the cluster, although they contribute less than 2% of the total mass.

The Pleiades have long been known to be a physically related group of stars rather than just a chance alignment. When studies were first made of the stars' proper motions, it was found that they are all moving in the same direction across the sky, at the same rate, further demonstrating that they were related. The cluster itself is moving at the leisurely pace of 32 km/sec towards the south of what is currently the constellation of Orion. Like most open clusters, the Pleiades will not stay gravitationally bound forever. Astronomers estimate that the cluster will survive for about another 250 million years, after which it will gradually disperse due to gravitational interactions with its galactic neighbourhood.

The Heart and Soul Nebula...

IC 1848 and IC 1805: The "Heart and Soul" nebula...

Objects: IC 1848 and IC 1805 (Sh2-199 and Sh2-190)

Type: Emission nebula

Constellation: Cassiopeia

Distance: 6,500 light years

Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD

Date: December 10th. 2021 (Ha frames), December 26th. (SII and OIII frames)

Subframes: 18 x 300s each for Ha (1x1), SII and OIII (2x2 binned), flats, bias as dark frames.

High overhead on winter’s evenings lies the constellation of Cassiopeia, an area of sky rich in star clusters and nebulae. A particularly large area of nebulosity lies on the Cassiopeia/Perseus border, the so-called “Heart and Soul” nebula (IC 1805 and IC 1848).

Stellarium map showing image field of view...

The complex covers an area of the sky over ten times as wide as the full moon and eight times as high (5.5 x 3.9 degrees). Despite its size, it is very faint and can only really be fully detected by long-exposure photography. Indeed, only the brightest portion (called NGC 896, a little knot of nebulosity on the north-western edge of the complex) was spotted by the eagle-eyed William Herschel in 1787 during his compilation of what became the NGC catalogue of "deep sky" objects. Edward Barnard latterly observed a larger area of nebulosity in the area, and gave it the designation of IC 1795 which includes the earlier Herschel discovery

In the late 1890’s, Barnard discovered IC 1805, describing it as “a cluster, considerably open, extremely large nebulosity extends following (to the east).” The star cluster he recorded (today usually referred to as Melotte 15) is that at the centre of the extended area of nebulosity that we today call IC 1805, although from his description there is no doubt that he also saw at least some of the surrounding glow.

Similarly, IC 1848 was discovered by Barnard at around the same time and was described as "a cluster, stars faint, extends …. to the east, in faint nebulosity." As with IC 1805, the entire nebula of IC 1848 has come to be regarded by the designation originally given to the star cluster and its immediate nebulosity.

The Heart and Soul complex are emission nebulae that form a vast star-forming complex that resides in the Perseus spiral arm of our Milky Way galaxy. The complex is 580 light-years across and comprises of giant bubbles of intensely hot, rarefied gases that are being blown into the dust surrounding the central cluster stars and rendered fluorescent by the intense radiation emitted by these hot young stars. These stars are less than a few million of years old; youngsters in comparison to stars like the sun, which is nearly 5 billion years old.

Annotated image showing designations of objects shown...

The annotated image above shows the designations of some of the objects visible.

The Soul Nebula complex (IC 1848) is also designated by its Sharpless catalogue number of Sh2-199. I have no idea what a “Soul” is supposed to look like: some U.S. astrophotographers refer to it (rather ghoulishly, I think) as the “Embyro” nebula: personally, it rather reminds me of the little Space Invaders from the 1980’s arcade game.

Within the Soul Nebula is a small patch of bright nebulosity designated at IC 1871 (Lynds Bright Nebula 637), that itself contains a dark dust nebula sometimes referred to as the “Whirling Dervish” nebula (a name also given to NGC 3247 in the southern hemisphere). A small knot of nebulosity to the south of IC 1848 has been designated at Sh2-198, with a similar knot to the north designated as Sh2-196. Just to the south-west of Sh2-196, a group of three other tiny Sharpless nebulae can be seen, Sh2-193, Sh2-192 and Sh2-194. The bright star cluster NGC 1027 (discovered by Herschel in 1787) lies just to the south-west of these.

The Heart Nebula, IC 1805, is also designated as Sh2-190, which includes NGC 1795/NGC 896, an area of nebulosity referred to by some astrophotographers (with their usual lack of imagination) as the “Fish-head” nebula.  The central cluster Melotte 15 is evidenced, with some of the associated dust columns. The small but bright star cluster Markarian 6 is visible on the south-western border of IC 1805.

Of particular interest are the two faint galaxies at the bottom of the above image, Maffei 1 and 2. These galaxies form part of a local galaxy group some 10 million light years away. Both were originally thought to be galactic nebulae, with Maffei 2 even being given a Sharpless designation (Sh2-195/197). Their light is heavily masked by dust lying in the galactic plane of our own galaxy, and they were only recognised in 1968 by infra-red observations.

In terms of my own imaging, the colour image was compiled from data obtained from narrowband Ha, SII and OIII images. The Ha signal is quite strong and indeed, was actually obtained through high haze without too much “noise” creeping in. Unfortunately, my polar alignment was a bit off and I had to manually stack the Ha images using an old AIP4Win programme (which can handle field rotation, unlike the version of Astroart that I normally use). This doesn’t let you remove hot pixels as part of the stacking process though, so some faint “streaks” can be seen in the final image if you look closely.

The SII and OIII signals are considerably fainter and required 2x2 binning.

I removed the stars from the narrowband channels using Starnet, then combined them as RGB (Ha/SII/OIII) in PSP7. This gave a rather greenish image, one that I corrected by over-laying a red mask of the Ha channel as a “colour” layer at around 20%.

The stars were added back in using unstretched narrow-band data as above, with a similar red correction.

A final overlay of the Ha data (stars reduced by the “erode” function in PSP) was added as a luminance layer to improve the detail in the nebulosity.

The Cygnus Loop...

The Cygnus Loop (Sharpless 2-103)...

Objects NGC 6992-5, IC1340 (the Eastern Veil), NGC 6960 (the Western Veil or "Witches Broom"), "Pickering's Triangle" (wedge of nebulosity at "one-o-clock" position above): also NGC 6974 and NGC 6979 (knots of nebulosity to the left of Pickering's Triangle)

Type: Supernova remnant
Constellation: Cygnus
Distance: 2,400 light years

Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: August 8th. 2022

Subframes: 18 x 300s for Ha, 12 x 300s for OIII, flats, no darks (hot pixel removal in Astroart). 

High overhead on a summer’s evening can be found the constellation of Cygnus (The Swan), whose brightest star (Deneb) is the top left star of the isosceles triangle of bright stars that dominates the UK summer night-time skies called the Summer Triangle.

Tucked under the Swan’s eastern wing is an enigmatic object, a supernova remnant called the Cygnus Loop. It consists of a bubble of dust filaments and fluorescent gas over 120 light years in diameter, or about 3 degrees across (6 moon diameters) as viewed from Earth, the remains of a supernova that occurred some 15,000 years ago.

The shock wave from that event is ploughing through and compressing the patchy interstellar medium of gas and dust that surrounded the exploding star, causing the rarefied gasses to fluoresce, hence the nebula we see today.

The brighter sections of the Cygnus Loop, NGC 6992-5 (the Veil Nebula) and NGC 6960 (The “Witches Broom”) are just visible through a large (8-inch aperture or more) telescope on clear, moon-free nights. Details of the central area of the bubble can only be detected on long exposure photography.

The five-minute subframes I used here weren’t really long enough to show up all of the available detail, and the stacks required a hefty tangential stretch to show the wispy central areas of nebulosity.

I used Starnet+ to remove the fog of stars in the stacked hydrogen-alpha and OIII images, which allowed some selective stretching and sharpening of the nebulosity. I then used the PSP “erode” function (“magic wand” to select background > invert > feather (3 pixels) > effects > edge > erode) to reduce the star sizes on the “normal” images, and combined the “starry” and “non-starry” images in “blend lighten” mode to give sharp nebulosity and small stars.

To make the colour image, I used the Ha channel as red, the OIII channel as blue and made an artificial green channel of 60/40 OIII/Ha. Combining the three as an RGB image gave the result at the top of this post.

The Great Orion Nebula...

Messier 42; The Great Orion Nebula...

Object: M42/NGC 1976/(Sharpless 2-281)

Type: Emission nebula
Constellation: Orion

Distance: 1,350 light years

Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: February 1st. 2022

Subframes: 24 x 30s, 24 x 60s, 12 x 300s for Ha, 12 x 300s for RGB each, flats, no darks (hot pixel removal in Astroart). 

NGC 1499: The California Nebula...

NGC 1499 (Sh2-220): The "California" Nebula...

Objects: NGC 1499 (Sharpless 2-220)
Type: Emission nebula
Constellation: Perseus
Distance: 1,450 light years

Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: January 5th. 2022

Subframes: 24 x 300s for Ha, 9 x 300s for SII, 12 x 600s (2x2 binned) for OIII each, flats, no darks (hot pixel removal in Astroart). 

Discovered on November 3, 1885 by Edward Barnard, the California Nebula (NGC 1499) is a large emission nebula and star-forming cloud approximately 100 light-years in length, located in the Orion spiral arm of the Milky Way galaxy (where our Solar System is also located) in the constellation of Perseus. It is believed to be one of the nearest H II emission regions to Earth. It is so named because it allegedly resembles the outline of the US State of California. It has a very low surface brightness and it is very difficult to observe visually.

Stellarium map showing the location of NGC 1499

The nebula can be found on winter evenings high in the northern hemisphere sky in the “tail” of the constellation of Perseus, just above the Pleiades and right next to the bright star Xi Persei.

This hot blue-white star is the brightest star in the above image, just right of centre. Xi Persei is indeed one of the hottest stars visible in the night sky; its surface temperature is about 37,000 Kelvin (about 66,000 degrees Fahrenheit, or more than six times hotter than the Sun). Because of its high temperature, it appears blue-white to the human eye. It has about 40 times the mass of the Sun and gives off 330,000 times the amount of light. Xi Persei is a runaway star, and the fast stellar wind it blows is piling up in front of it to create a shock wave. This shock wave is heating up dust.

Xi Persei, which is receding from us at about 20 kilometres per second, is a member of an association of very hot stars that were born within the California nebula only a few million years ago. These massive and luminous stars are lighting up the nebula, as well as heating and ionizing it. In visible light, the ionized gas glows red, while in infrared light we see the heated dust. 

Conditions were quite good, with a clear, dark, moonless sky for once, although the Ha frames were interrupted by some transient clouds for an hour or so, which put the sequence back a bit.  As a result, I only got nine SII frames before the target went behind my house. 

24 x 300s H-alpha stack, starless

12 x 600s 2x2 binned stack OIII stack, starless...

9 x 300s SII stack, starless...

The OIII data was quite faint and noisy (hence the 600s binned frames) and a good flat field was an absolute must in pulling out what faint signal there was from the background. Even then I was a bit sceptical that what I had wasn’t just a result of vignetting, but it seemed to match the OIII area in other people’s images. 

I removed the stars from the stacked and stretched channel images with Starnet++ which allowed some selective stretching and sharpening.  I then RGB combined the starless images in PaintShop Pro to give a colour starless image. I added the Ha luminance frame back over the colour image at around a 25% blend level, which helped to sharpen the whole thing up a bit without washing out the colour too much. Subtraction of the starless images from their respective original frames gave RGB channels for a star field.  Once combined, I pasted them back into the starless RGB frame in “screen” mode.  

I had not realised just how much this nebula tails off to the south-east and so it wasn’t particularly well-centred in the frame, hence a fairly heavy crop to give the final image above.

Reference: 

http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/the-california-nebula-ngc-1499/

Messier 31: The Great Andromeda Galaxy...

M31: The Great Andromeda Galaxy...

Object: Messier 31 (The Great Andromeda Galaxy, M31, NGC 224)

Type: Spiral galaxy (classification SA(s)b)
Constellation: Andromeda
Distance: 2.54 million light years

Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: November 4th. 2021
Subframes: 12 x 300s and 12 x 20s for Luminance, 200s for RGB each, flats, no darks (hot pixel removal in Astroart).

This object has always been a bit of a nemesis for me, and this image still shows my struggle with it. It is noisy and the star shapes are appalling, but it will have to do for now until I have another go next year. In many ways, my earlier monochrome image of it is better.  Nevertheless, it does show the spiral structure and the two satellite galaxies M32 and M110 (the two white ovals at 7 o’clock and 1 o’clock respectively, relative to the centre of the main galaxy).

Messier 31 (M31), better known as the Andromeda Galaxy, is a large spiral galaxy located in the constellation Andromeda and is the nearest major galaxy to our own.

The Andromeda Galaxy is one of the most distant deep sky objects visible to the naked eye. It is relatively easy to find high in the autumn Northern hemisphere sky as it is one of the brightest Messier objects.

Stellarium map showing location of M31...

The earliest record of M31 comes from the Persian astronomer Abd al-Rahman al-Sufi, who mentioned the object as being in the constellation of Andromeda (the Chained Maiden) in his Book of Fixed Stars in 964, describing the galaxy as a “small cloud.”

The first documented telescopic observation of the galaxy was provided by the German astronomer Simon Marius on December 15, 1612. He described the object as resembling “the flame of a candle as seen through transparent horn”.

Charles Messier credited Marius for the discovery of M31, unaware of the Persian astronomer’s earlier observations.

In 1887, Welsh engineer and amateur astronomer Isaac Roberts took the first photographs of the Andromeda Galaxy from Sussex, England. His long-exposure images revealed the galaxy’s spiral structure for the first time.

Binoculars and small telescopes reveal only the galaxy’s bright core, but larger instruments show its full size, which is six times larger than the apparent diameter of the full Moon. The Andromeda Galaxy has a total of 14 satellite galaxies, of which Messier 32 and Messier 110 are the largest and easiest to observe.

Messier 31 is inclined at about 77 degrees relative to Earth. As a result of gravitational interaction with the nearby galaxies, it has a notable S-shaped warp rather than a flat disk.

Messier 31 is the largest and most massive member of the Local Group of galaxies, which also includes our Milky Way, the Triangulum Galaxy (M33) and more than 40 smaller galaxies. The Andromeda Galaxy contains a trillion stars, more than twice as many as the Milky Way, which is home to 200 to 400 billion stars. In 2005, M31 was discovered to have a large extended stellar disk, spanning more than 220,000 light years in diameter. The galaxy was previously thought to have a diameter between 70,000 and 120,000 light years.

The Andromeda Galaxy was long believed to be a nebula in our own galaxy and was known as the Great Andromeda Nebula. It wasn’t until 1917 that this belief started to be questioned. American astronomer Heber Curtis saw a nova within the galaxy and, after going over the photographic record, found 11 more novae in the region. He noticed that the novae within M31 were about 10 magnitudes fainter than those observed elsewhere in the sky and came up with a new distance estimate for the object: 500,000 light years.

Curtis became a proponent of a new theory which introduced the idea that the objects known as spiral nebulae were in fact independent galaxies. The theory was known as the “island universes” hypothesis. The term “island universes” came from German philosopher Immanuel Kant, who also believed that spiral nebulae were not part of our galaxy.

In 1920, Curtis debated the nature of spiral nebulae and the size of the universe with Harlow Shapley in what is known as the Great Debate or the Shapley-Curtis Debate. The debate took place on April 26 at the Smithsonian Museum of Natural History. Shapley argued that spiral nebulae were part of the Milky Way and that the universe was composed of only one large galaxy, while Curtis contended that spiral nebulae were separate galaxies and that the Milky Way was just one of many galaxies.

The true nature of M31 was not proven until 1923, when Edwin Hubble established the intergalactic distance between Andromeda and the Milky Way. Using the 100-inch Hooker Telescope at Mount Wilson Observatory in Los Angeles, Hubble identified Cepheid variable stars on astronomical images of M31.

Hubble’s original estimate placed M31 at an approximate distance of 750,000 light years from Earth, which finally proved that the object resided outside of our galaxy.  Further observations by German astronomer Walter Baade identified that the stars within the galaxy fell into two population types: Type I and Type II, with each type having a distinct kind of Cepheid variable and which led to distance estimates for M31 doubling.

Messier 31 is approaching the Milky Way at about 110 km/s. It is one of the few blue-shifted galaxies (moving toward us) from our point of view. The two galaxies are roughly equal in mass and will collide in about 3.75 billion years. The collision will most likely result in a merger of the two large galaxies into a giant elliptical galaxy, and possibly even a large disk galaxy. 

IC 1396 (Sharpless 2-131)...

IC 1396....

Objects: IC 1396 (Sh 2-131)

Type: Emission nebula
Constellation: Cepheus
Distance: 2,450 light years
Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: July 18th. 2021
Subframes: 12 x 300s for Ha, SII and OIII each, no flats, no darks (hot pixel removal in Astroart).
 

Discovered in August 1893 by Edward Barnard, IC 1396 is a large HII region in the constellation Cepheus, spanning 3 full degrees (170 by 140 arc-min), the same angular distance of 6 full moons. It formed at the southern edge of an enormous 400 light year bubble of molecular gas known as the Cepheus bubble.

Stellarium map showing image field of view

The IC 1396 complex fluoresces from the intense radiation of the 4th-magnitude variable star near its centre, the class O6 star HD206267, a blue supergiant. HD206267 is a member of the cluster, known as Trumpler 37, believed to be the core of the expansive Cepheus OB2 association. HD206267 is a trapezium type stellar system with HD206267 as the dominant ultraviolet energy source with a smaller UV contribution from three cooler companion B0 type stars. The stars of the entire Trumpler 37 cluster are about 7 million years old, although HD206267 formed more recently about 4 million years ago.

A distinct feature of IC 1396 is the radial arrangement of several bright rimmed globules that form a loose and slowly expanding ring around the illuminating stars. The ring of loosely arranged dark globules has a radius of about 40 light years with HD206267 at its centre. Although several of the globules are optically conspicuous, the most prominent is catalogued as IC 1396A, nicknamed the “Elephant’s Trunk” (previously imaged here). IC 1396A contains the well known reflection nebula vdB 142. Low and intermediate mass stars appear to be actively forming within the globules. The star formation within the globules has been induced by a process known as "radiation driven implosion" where the ultraviolet flux from a massive star like HD206267 compresses the cold molecular gas within the globules, thus triggering collapse of the cloud and subsequent formation of lower mass stars.

The history of IC 1396 suggests a complex interplay of sequentially-triggered star formation and cloud-cloud interactions. An initial burst of star formation occurred between 13 and 18 million years ago and gave rise to the first generation of stars, which includes the existing nearby cluster NGC 7160. The more massive members from that first generation of stars went on to destroy themselves in supernovae explosions and no longer exist today. About 7 to 8 million years ago the effects of the first generation of supernova driven shock fronts and powerful stellar winds from existing stars created a huge 400 light year diameter bubble known as the Cepheus bubble. The expanding bubble compressed and flattened surrounding molecular clouds triggering a second burst of star formation which went on to form the Cepheus OB2 association some 7 million years ago.

Also formed in this second generation of star formation were Trumpler 37 and its dominant star, HD206267 some 4 million years ago. Under the influence of the ionizing radiation field from the new star cluster, the HII cloud IC 1396 and its globules formed some 2 to 3 million years ago. Triggered by the expanding Cepheus bubble, many well known HII regions have formed along its perimeter including IC 1396, Sh2-129, 133, 134, and 140.

As IC 1396 expanded from the stellar winds of HD206267, surviving fragments of molecular clouds in the form of globules formed into an expanding ring around the central exciting star. The third and youngest generation of lower mass stars is currently forming within the dark globules of IC 1396A by the process of radiation driven implosion (see above).

The bright orange star just to the north of IC1396 is the supergiant μ (mu) Cephei. It formed during the first generation of stars which created the Cepheus bubble. It has the distinction of being one of the most luminous stars in our galaxy, emitting 350,000 times the power of our sun. Also known as Herschel's Garnet Star, it is the prototype of  μ-Cephei type variables. It is a red supergiant of irregular brightness, varying from about magnitude 3.5 to 5 over a period of two to two and a half years. Its mass is estimated at 15 times that of the Sun, and it is one of the largest stars known (the best part of two billion miles across at maximum size). It is a very cool star (only about 3700°C), so most of its radiation is in the infrared. Its visible radiation is about 40,000 times that of the Sun, and taking into account absorption of its light by interstellar dust and the large proportion of infrared radiation it must give off, its total luminosity must be nearly ten times greater, or about 350,000 solar luminosities. The star is near the end of its life, having already begun to fuse helium into carbon in its core, and within a few million years will expire in a supernova explosion, leaving behind nothing but (most likely) a black hole or (less likely) a neutron star.

The image above is a 1:1:1 RGB compilation of the narrowband data (Ha=R, SII=G, OIII=B).  I did do a Starnet version with RGB stars added back in but it looked essentially like the image above, but with muted stars, and I think the star-strewn field looks more natural in this case. There was a bad dose of field rotation in the stacked frames and my polar alignment must have been off, something I will check next time out.

Curiously, the IC 1396 complex itself doesn’t have a popular nickname, often being regarded as merely an extension of its “Elephant’s Trunk” component.  I always think it looks like a large figure-of-eight. For some reason, it reminds me of one of those sickly ice-cream lollies from the early Eighties, “Funny Faces”, though the thought of IC 1396 being called the “Funny Face nebula” is too awful to contemplate.

References:

http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/ic-1396/

http://www.starrywonders.com/ic1396NBsmall.html

https://cseligman.com/text/atlas/ic13a.htm

http://www.robgendlerastropics.com/IC1396text.html

IC 1318...

IC 1318, the Gamma Cygni nebula...

 

Objects: Gamma Cygni nebula (also designated as IC 1318, Sharpless 2-108) 
Type: Emission nebulae
Constellation: Cygnus
Distance: 4,500 light years
Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: July 17th. 2021
Subframes: 12 x 300s for Ha, SII and OIII each, no flats, no darks (hot pixel removal in Astroart).

High overhead on summer evenings in the UK lies the Summer Triangle of bright stars comprising of Altair, Vega and Deneb. Deneb marks the tail of the celestial swan, Cygnus, through which runs the silvery streak of the Milky Way, down past Altair to the horizon. The area of Cygnus is particularly rich in star clouds, dark patches of interstellar dust and nebulae. One such area is clustered around the central star of the Northern Cross of Cygnus, and is called IC 1318.

Map showing field of image view... 

Discovered in August 1893 by Edward Barnard, IC 1318 is an emission nebula with an apparent size of 50 x 30 arc-min (or two full moons, side by side).

IC 1318 (Sh2-108) is commonly referred to as the “Gamma Cygni nebula” because of its apparent proximity to the F8Iab supergiant star (also called Sadr). γ Cygni is in fact a foreground object, lying 1,800 light-years from Earth. The nebula lies far beyond Gamma Cygni, in the depths of the Cygnus X complex of star formation regions some 4,500 light years away.

The nebulosity appears to contain a supernova remnant. Drake (1959) discovered a nebula about 3' southeast of γ Cygni in a pass-band centred near Ha. He also found that it was absent on a well-exposed blue-sensitive plate, and suggested that it is an H II region and not a reflection nebula. This “γ Cygni nebula” is buried in the photographic halation of the star so that it is not apparent on many plates such as the Palomar Sky Survey plate of the region, and it is not identical with an HII region 3° in diameter, S108 (Sharpless 1959), also called the “γ Cygni nebula.” Following Drake’s discovery, Mathewson, Large, and Haslam (1960), found a non-thermal radio source, or a component of confused sources, near the position of the small γ Cygni nebula, and they called it the “γ Cygni source.” It is the fourth-brightest supernova remnant at 400 MHz in the catalogue of Downes (D4, 1971). The nebula is also called DWB 63 and is the location of the radio source W66. According to Russian astronomer Veta Avedisova, DWB 63 is ionised by Gamma Cygni, the O8 V class HD 229202 and the B2 Ib supergiant HD 193946.

Avedisova also includes Sh 2-108 in star formation region SFR 78.18+1.82 along with infrared star cluster [BDB2003] G077.46+01.76 and numerous other nearby HII regions.

A band of dust runs across the region, appearing to divide part of the emission nebulosity in two and giving rise to the areas sometimes referred to as IC 1318A and IC1318B, also known as the “Butterfly Nebula”.

Tucked down at the bottom right-hand side of the above image can be seen the NGC 6888, the Crescent Nebula, which I have previously imaged in a much narrower field of view.

The above image is a blend of 1:1:1 RGB from Ha/SII/OIII narrowband data, with a starless (“Starnetted”) version with stars (20 x 15s each for RGB) added back in, to reduce the “starfog” caused by the background Milky Way.

References:

https://cseligman.com/text/atlas/ic13.htm

http://articles.adsabs.harvard.edu/pdf/1974ApJ...194..337J

http://galaxymap.org/cat/list/sharpless/101