mental4astro
03-07-2013, 12:38 AM
Good evening, my fellow "nocturnians",
It has been a very long time since The Challenge was issued. With Scorpio high overhead at this time of the year, I thought it appropriate to delve into the occult side of astronomy - dark nebulae.
These darkest of features of the sky tend to reveal themselves only when one is at a dark site. Their very nature sees them recoil out of view at the mere hint of light pollution, almost skulking way from the light. But their true nature is very diverse - some the cloaking cocoon of proto stars that await the ignition of their nuclear fire, others the remnant gas and dust left over from stellar formation that lingers in the interstellar space like the smoke of an extinguished match.
With the blaze of the Milky Way's hub overhead, these rarely chased features come into a league of their own by obscuring the background glow of our home galaxy. Now is the time to chase these shadows in the sky.
Naked eye
From a dark site, these dark features can be easily seen tracing lines through the band of the Milky Way. They form some very interesting features that resemble terrestrial creatures, such as the "Dark Horse of Sagittarius" (http://en.wikipedia.org/wiki/File:GreatDarkHorse_Nebulae.jpg), and the "Emu in the Sky" (http://aboriginalastronomy.blogspot.com.au/2011/04/coal-sack-and-emu-in-er-i-mean-llama-in.html) from Aboriginal sky lore. The Southern Cross harbours the famous "Coalsack Nebula" (http://www.farnham-as.co.uk/wp-content/uploads/2013/05/2.-SouthernCross-Pointers-Eta-Carinae-Nebula-text.jpg) that actually forms the head of the "Emu".
Binoculars
The inky blackness of the Coalsack is very striking from a dark site. This cloud of molecular gas and dust that never got formed into a star or planet just lingers within the Milky Way, waiting for the chance to be formed into something more than just gas and dust. Panning a pair of binos east from the Southern Cross, the background glow of the Milky Way abruptly stops on entering the Coalsack. And a beautiful juxtaposition of light and dark is had when the Jewel Box is gained into the field of view - It really is a gorgeous sight the brilliance of the Jewel Box with the "rude" blackness of the Coalsack.
The brilliant globular cluster Omega Centauri is surrounded by soft, tenuous fingers of dark nebulosity. These details are rarely noticed for the brilliance of Omega. Binoculars offer the best chance to view these details of variations in the illumination of the background glow.
M7, the giant open cluster at the base of the stinger of Scorpio also is home to some fabulous dark nebulosity, really only noticed with the rich field of binoculars. The cluster is criss-crossed with soft lines of dark, and a fantastic dark ribbon licks the edge of M7 (called B283). This is one of my favourite compositions made by these two DSO's.
Eta Carina, the magnificent emission nebula, is marked by the dark lines that form its lobes. Binoculars here show how expansive this nebula is, and how delineated it is by dark material. It is a fabulous vista this expanse, with so much mottling of the whole field. I'll review Eta a little more in the Telescope section below too.
One last thing with binos and a dark site - slowly scan the heavens, regardless of the time of year. Big binos, 70mm and up, will show a staggering amount of detail in the sky, even in areas that seem devoid of much influence of the Milky Way. Big binos will show the softest of variations in the background sky glow that telescopes will just miss altogether. It is these quietly spoken details that can be so charming.
Telescopes
Here we hunt down the occult demons. Serpent like structures can be teased out in bright nebulae. Splashes of pure black, almost like angles have lifted a tiny veil in the sky to allow us to peer into the beyond. And the tell-tale signs of massive stellar activity as massive shockwave fronts are formed. Here the powers of the occult prevail...
Eta Carina. The super massive star that lends its name to this nebula is in its death throes, experiencing spasmodic eruptions as its spent hydrogen fuel struggles to maintain its balance between equilibrium and cataclysmic collapse. These eruptions have created a shock wave that's rushing out from this star. The wonderful dark structure that is "The Keyhole" (http://imgsrc.hubblesite.org/hu/gallery/db/tours/tour-carina/tour.swf) forms the foreground limb of this shock wave. The dark nebulosity that forms the Keyhole is full of fine soft details. Ironically, right next to the soon-to-happen supernova is an area rich in stellar formation. The sharp edge of the Eta Carina nebula show fantastic dark pillars. The surrounding "light" area of the glowing gas and dust is being open up by the energy of the newly formed star cluster Trumpler 14. Yet the tell tale signs of stellar formation is seen in the dark fingers that form the dark pillars. Here, the gravitational pull of proto stars holds the surrounding gas and dust that is otherwise being blown away by the nearby star cluster. These dark pillars will eventually too be blown away when the nuclear fire of these proto stars kicks in.
"The Ink Spot Nebula" (http://www.waa.at/bericht/2010/07/20100709-11hwp/20100710api2-12-n6520.jpg), aka B86, is a stunning raven black nebula. Immediately next to a brilliant, compact open cluster, NGC 6520, the contrast between light and dark is just stunning. The all pervasive brilliance of this area of the Milky Way just stops with a BANG! It sits on the edge of the densest star cloud in the entire sky, and is truly stunning. Sneaking its way between M7 and M8, it inconspicuously goes about its occult business. Just beautiful.
My last offering is a mix of several distinct objects in the one field of view that can be a little challenging. These objects are on the boundary of Corona Australis and Sagittarius. Dark nebula Be 157 is surrounded by the soft glow of a two distinct reflection nebula (NGC6826/7, NGC 6729 & IC 4812) and the lovely globular cluster NGC 6823. This grouping is a lovely spectacle in just about any scope. Different eyepieces are recommended to be used as this will give a variation in contrast, magnification, and field of view, all combining to enhance different aspects. This amazing image of this area (http://www.martinpughastrophotography.id.a u/images/NGC6726-25pct_Labelled.jpg) was taken by fellow IISer Martin Pugh. It shows the incredible expanse and detail that is area.
I hope this Challenge provides some new targets to chase for you, or a new view on them. Dark nebulae tend to be forgotten, and pushed away from our thoughts due to the colourful brilliance of their loud cousins. But they can provide a lot of insight into the forces that create and change this vast galaxy that is our home. I hope you can add some more dark objects to this listing too.
Mental.
It has been a very long time since The Challenge was issued. With Scorpio high overhead at this time of the year, I thought it appropriate to delve into the occult side of astronomy - dark nebulae.
These darkest of features of the sky tend to reveal themselves only when one is at a dark site. Their very nature sees them recoil out of view at the mere hint of light pollution, almost skulking way from the light. But their true nature is very diverse - some the cloaking cocoon of proto stars that await the ignition of their nuclear fire, others the remnant gas and dust left over from stellar formation that lingers in the interstellar space like the smoke of an extinguished match.
With the blaze of the Milky Way's hub overhead, these rarely chased features come into a league of their own by obscuring the background glow of our home galaxy. Now is the time to chase these shadows in the sky.
Naked eye
From a dark site, these dark features can be easily seen tracing lines through the band of the Milky Way. They form some very interesting features that resemble terrestrial creatures, such as the "Dark Horse of Sagittarius" (http://en.wikipedia.org/wiki/File:GreatDarkHorse_Nebulae.jpg), and the "Emu in the Sky" (http://aboriginalastronomy.blogspot.com.au/2011/04/coal-sack-and-emu-in-er-i-mean-llama-in.html) from Aboriginal sky lore. The Southern Cross harbours the famous "Coalsack Nebula" (http://www.farnham-as.co.uk/wp-content/uploads/2013/05/2.-SouthernCross-Pointers-Eta-Carinae-Nebula-text.jpg) that actually forms the head of the "Emu".
Binoculars
The inky blackness of the Coalsack is very striking from a dark site. This cloud of molecular gas and dust that never got formed into a star or planet just lingers within the Milky Way, waiting for the chance to be formed into something more than just gas and dust. Panning a pair of binos east from the Southern Cross, the background glow of the Milky Way abruptly stops on entering the Coalsack. And a beautiful juxtaposition of light and dark is had when the Jewel Box is gained into the field of view - It really is a gorgeous sight the brilliance of the Jewel Box with the "rude" blackness of the Coalsack.
The brilliant globular cluster Omega Centauri is surrounded by soft, tenuous fingers of dark nebulosity. These details are rarely noticed for the brilliance of Omega. Binoculars offer the best chance to view these details of variations in the illumination of the background glow.
M7, the giant open cluster at the base of the stinger of Scorpio also is home to some fabulous dark nebulosity, really only noticed with the rich field of binoculars. The cluster is criss-crossed with soft lines of dark, and a fantastic dark ribbon licks the edge of M7 (called B283). This is one of my favourite compositions made by these two DSO's.
Eta Carina, the magnificent emission nebula, is marked by the dark lines that form its lobes. Binoculars here show how expansive this nebula is, and how delineated it is by dark material. It is a fabulous vista this expanse, with so much mottling of the whole field. I'll review Eta a little more in the Telescope section below too.
One last thing with binos and a dark site - slowly scan the heavens, regardless of the time of year. Big binos, 70mm and up, will show a staggering amount of detail in the sky, even in areas that seem devoid of much influence of the Milky Way. Big binos will show the softest of variations in the background sky glow that telescopes will just miss altogether. It is these quietly spoken details that can be so charming.
Telescopes
Here we hunt down the occult demons. Serpent like structures can be teased out in bright nebulae. Splashes of pure black, almost like angles have lifted a tiny veil in the sky to allow us to peer into the beyond. And the tell-tale signs of massive stellar activity as massive shockwave fronts are formed. Here the powers of the occult prevail...
Eta Carina. The super massive star that lends its name to this nebula is in its death throes, experiencing spasmodic eruptions as its spent hydrogen fuel struggles to maintain its balance between equilibrium and cataclysmic collapse. These eruptions have created a shock wave that's rushing out from this star. The wonderful dark structure that is "The Keyhole" (http://imgsrc.hubblesite.org/hu/gallery/db/tours/tour-carina/tour.swf) forms the foreground limb of this shock wave. The dark nebulosity that forms the Keyhole is full of fine soft details. Ironically, right next to the soon-to-happen supernova is an area rich in stellar formation. The sharp edge of the Eta Carina nebula show fantastic dark pillars. The surrounding "light" area of the glowing gas and dust is being open up by the energy of the newly formed star cluster Trumpler 14. Yet the tell tale signs of stellar formation is seen in the dark fingers that form the dark pillars. Here, the gravitational pull of proto stars holds the surrounding gas and dust that is otherwise being blown away by the nearby star cluster. These dark pillars will eventually too be blown away when the nuclear fire of these proto stars kicks in.
"The Ink Spot Nebula" (http://www.waa.at/bericht/2010/07/20100709-11hwp/20100710api2-12-n6520.jpg), aka B86, is a stunning raven black nebula. Immediately next to a brilliant, compact open cluster, NGC 6520, the contrast between light and dark is just stunning. The all pervasive brilliance of this area of the Milky Way just stops with a BANG! It sits on the edge of the densest star cloud in the entire sky, and is truly stunning. Sneaking its way between M7 and M8, it inconspicuously goes about its occult business. Just beautiful.
My last offering is a mix of several distinct objects in the one field of view that can be a little challenging. These objects are on the boundary of Corona Australis and Sagittarius. Dark nebula Be 157 is surrounded by the soft glow of a two distinct reflection nebula (NGC6826/7, NGC 6729 & IC 4812) and the lovely globular cluster NGC 6823. This grouping is a lovely spectacle in just about any scope. Different eyepieces are recommended to be used as this will give a variation in contrast, magnification, and field of view, all combining to enhance different aspects. This amazing image of this area (http://www.martinpughastrophotography.id.a u/images/NGC6726-25pct_Labelled.jpg) was taken by fellow IISer Martin Pugh. It shows the incredible expanse and detail that is area.
I hope this Challenge provides some new targets to chase for you, or a new view on them. Dark nebulae tend to be forgotten, and pushed away from our thoughts due to the colourful brilliance of their loud cousins. But they can provide a lot of insight into the forces that create and change this vast galaxy that is our home. I hope you can add some more dark objects to this listing too.
Mental.