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| Messier 42; The Great Orion Nebula... |
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| NGC 1499 (Sh2-220): The "California" Nebula... |
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| Stellarium map showing the location of NGC 1499 |
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.
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| 24 x 300s H-alpha stack, starless |
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| 12 x 600s 2x2 binned stack OIII stack, starless... |
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| 9 x 300s SII stack, starless... |
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.
http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/the-california-nebula-ngc-1499/
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| M31: The Great Andromeda 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.
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| Stellarium map showing location of M31... |
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
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
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
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.
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| IC 1396.... |
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| Stellarium map showing image field of view |
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
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| IC 1318, the Gamma Cygni nebula... |
High overhead on summer evenings in the
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| Map showing field of image view... |
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
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| NGC 7000 and IC 5070, the North America and Pelican nebulae (Sh2-117)... |
Objects: NGC 7000 (North America nebula), IC 5070 (Pelican Nebula)
Type: Emission nebulae
Constellation: Cygnus
Distance: 1,500 light years
Equipment: Atik 460/EFW 2, Samyang 135mm lens@ F2, Vixen GPDX mount, guiding with Lodestar X2/PHD
Date: July 15th. 2021
Subframes: 12 x 300s for Ha, SII and OIII each, no flats, no darks (hot pixel removal in Astroart).
Information about this object can be found in a previous blog entry here. Since I took that earlier image, the camera to lens spacing has been sorted out and the narrowband filters upgraded to reduce halos around stars. This has allowed me to acquire better quality data to support a colour image.
The above RGB image is from Ha/SII/OIII narrowband data (R=80:20 Ha/SII, G=70:30 SII/Ha, OIII=80/20 OIII/SII).
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| Moon (71% full) at 7.10pm GMT, 23rd March 2021 |
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| Messier 63 |
Messier 63 (M63, also known as the Sunflower Galaxy) was discovered in 1779 by the French astronomer Pierre Méchain and was the first of 24 objects that Méchain would contribute to Charles Messier’s catalogue.
High overhead on late Spring evenings, M63 is tucked away under the tail of the Great Bear in the obscure constellation of Canes Venatici. It can be seen in binoculars as a small, hazy patch of light or an out-of-focus star. The Stellarium sky map below shows M63’s location.
As seen in the sky from Earth, the galaxy occupies an area of 12.6 by 7.2 arc minutes, which corresponds to a spatial diameter of 98,000 light years. This makes it roughly the same size as the Milky Way, having a mass around 140 billion times that of the Sun.
Messier 63 has a distinctive appearance that gives rise to the “Sunflower” nickname, with a yellowish central disc and a number of short spiral arm segments dotted with starburst regions and dust lanes.
M63 is a prototype for a class of galaxies known as “flocculent spirals". Such galaxies seem to have many spiral arms that appear patchy and discontinuous, although infrared observations indicate that M63 is in fact a two-armed spiral structure.
Messier 63 is one of the members of the M51 Group, a group of gravitationally bound galaxies located in Canes Venatici, named after the brightest member of the group, Messier 51 (the Whirlpool Galaxy).
In 2011, astronomers discovered a tidal stellar stream in the galaxy’s halo. The faint giant arc-loop feature had been detected as early as 1979, but not connected to a minor merger with a dwarf satellite galaxy, disrupted as a result of interaction with M63. The stream of stars originated from the accretion of the smaller galaxy within the last 5 billion years. The fate of the dwarf galaxy is unknown, but the colour of the stars indicates that it was probably a galaxy belonging to the Local Group.
The recent and unprecedented run of overcast weather means that this winter’s nebula season has been pretty much clouded out. I have therefore packed away the refractor and decided to try and go for some galaxies using my ancient Vixen VC200L and a x0.71 focal reducer. I am hoping to capture some of the brighter spring galaxies, using short exposures so that I can complete imaging projects in a single night and not have to hope that I can get two or three clear nights to collect enough data.
This was a test run of the concept and it seemed to go OK. The subs appeared slightly vignetted and there were some horrible dust doughnuts, but a combination of flat fields and Astroart’s gradient removal tool seemed to clean up the worst of it all.
The exposures were not deep enough to clearly reveal M63’s tidal halo referenced above, but it was nice to get enough data for a colour image within three hours.
References:
1) https://www.nasa.gov/feature/goddard/2017/messier-63-the-sunflower-galaxy
2) https://www.cosmotography.com/images/small_ngc5055.html
3) https://www.messier-objects.com/messier-63-sunflower-galaxy/
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| Sharpless 2-273 |
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| Map showing image field of view |
At the centre of the nebulosity is the 4th-magnitude open cluster NGC 2264, which was discovered on Jan 18, 1784 by William Herschel.
The surrounding nebulosity is a complex consisting of dark absorption nebulae, emission nebulae, reflection nebulae, and the stars that illuminate or outline their structures. At one end of the brightest central area, the “Cone Nebula” is a dense cloud of gas and dust sculpted by stellar winds from an extremely hot, bright star which is completely hidden in visible light by the gas and dust in front of it. Scattered across the central area are a number of bright stars which look like lights strung on a Christmas tree (hence the cluster’s popular name of the “Christmas Tree cluster”) with the Cone Nebula at the apex of the tree, and the bright star S Monocerotis and the “Fox Fur Nebula” near the base. The Fox Fur nebula is not generally considered a part of NGC 2264, but is certainly an extension of the gas and dust filling the region, as all the stars and clouds of gas and dust lie at about the same distance from us.
I took a narrower field image of the area back in 2019, which shows this colourful area in more detail.
A Hubble Space Telescope view (below left) of the Cone Nebula shows the dense clouds of gas and dust in a region only a couple of light years across. The overall size of the Cone is about 7 light years.
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| Cone nebula in visible light (left), NGC 2264 in IR (right) |
Just to the southwest of the Cone Nebula lies a tiny fan of nebulosity designated as NGC 2261. It appears as a tiny comet-shaped blob on the image above (enlarged below).
Although discovered on Dec 26 1783, by William Herschel, the nebula is named after the American astronomer Edwin P. Hubble, who carried out some of the early studies of this object.
It is a fan-shaped cloud of gas and dust which is illuminated by R Monocerotis (R Mon), the bright star at the bottom end of the nebula. Dense condensations of dust near the star cast shadows out into the nebula, and as they move the illumination changes, giving rise to the variations first noted by Hubble. The star itself, lying about 2,500 light-years from Earth, cannot be seen directly, but only through light scattered off of dust particles in the surrounding nebula. R Mon is believed to have a mass of about 10 times that of the Sun, and to have an age of only 300,000 years. There is probably a symmetrical counterpart of the fan-shaped nebula on the southern side of the star, but it is heavily obscured from view by dust lying between this lobe and our line of sight.
This image was my first in over 3 months, thanks to almost continuous cloud cover in my corner of the world. As always seems the way, the evening of February 26th. was plagued by a high haze and a 100% full moon, but was adequate for H-alpha imaging. Of the 12 x 600 sub-frames I collected before the haze became too dense, I had to discard two due to bright aircraft trails (what lockdown travel restrictions are they subject to, then?). Fortunately, a later bonus (and completely un-forecast) string of clear, moonless evenings in early March allowed me to get some RGB colour data as well.
The subs for each channel were sigma stacked in Astroart, with the result treated with AA’s gradient removal tool and then given a log stretch. Each stacked channel was then run through Starnet and the resultant starless image given an edge preserving smooth and “clarified” in Paint Shop Pro. This proved particularly effective for the R, G and B stacks, where the stars were otherwise overpowering: Starnet allowed the dog to see the rabbit when attempting to pull out nebulosity, especially in the blue channel.
The starless stacks are shown below:
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| Ha channel - stars removed with Starnet |
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| Red channel - starless |
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| Green channel - starless |
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| Blue channel - starless |
The R(R = 70:30 R/Ha), G and B channels were colour combined in PaintShop Pro to give this rather striking RGB starless image...
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| RGB starless combination |
A less aggressively stretched version of each of the R, G and B stacks to exclude nebulosity was given a Gaussian blur to tidy up the rather under-sampled stars, then RGB combined, star-reduced, then given a hefty saturation tweak to produce a colour star layer...
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| RGB star layer |
This was pasted back over the starless HaRGB image in screen mode, with some final selective sharpening and contrast/colour adjustment in PSP to give the final image.
References:
1) https://cseligman.com/text/atlas/ngc22a.htm#2264
2) https://hubblesite.org/contents/media/images/1999/35/904-Image.html
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| Conjunction of M45 and Mars |
