Bartel har varit ute med sina små snabba teleskop.
Betänk vad man kan se med teleskop som är i den här storkeken man kan ta under armen.
I've finished my research project on the history of IFN Integrated Flux Nebula observations. I find it quite interesting.
Herschel's Ghosts by Mel Bartels
Waiting for my eyes to dark adapt, I pace back and forth under the crisp winter sky that’s punctuated by brilliant blue- white stars. The constellation Cassiopeia shepherds the remnants of the summer Milky Way to the northwest horizon, Orion ascends from the southeast horizon and the Pleiades, the seven sisters of mythology, first viewed through a telescope by Galileo, are nearly overhead. My newly minted 6 inch F2.8 telescope sits on a table, ready for first light. The 21mm Ethos 100 degree eyepiece dominates the tiny scope; indeed, I offset the scope’s center of gravity with this massive eyepiece in mind.
After a few minutes my eyes sufficiently dark adapt and I decide on the Pleaides as my first target. How will the little scope perform? I center on the star cluster and begin looking. Wow, the incredibly wide 4.5 degree field of view swallows the cluster. The Pleiades’ stars shine brilliantly through the eyepiece; the Merope nebula looks like a waterfall. My eye notices a smudgy ring of grayness surrounding the cluster at the edge of the field. What? Is there something wrong with my baffling? Is there some sort of fog in the eyepiece or coma corrector? I move the scope back and forth; the bubble stays painted on the sky. Maybe the stars are casting some sort of glow? I follow the ring all the way around, keeping the cluster near the edge. No, it’s real, a real mystery.
Afterwards I search online for images of the Pleiades. I find a particularly deep digital image many hours long that shows the bubble. I share the view with others: they too can see it. Walking back to their scopes, it’s visible too, albeit not as easy with the narrower field and higher magnifications. Howard Banich points out that the German astronomer Wilhelm Tempel observed the bubble in the late 1800’s. Later Walter Scott Houston in his Deep Sky Wonders column in Sky and Telescope magazine mentions that “on really exceptional nights the glow swells out to encompass the entire cluster in a big cocoon."
For many years amateurs have disagreed over the Andromeda Galaxy’s extent, claiming widths from three to five degrees. Through my little telescope the Andromeda Galaxy’s edges merge with the Milky Way. If the ghostly Milky Way extensions are visible, then the galaxy appears five degrees wide; if not, then the Andromeda Galaxy appears three degrees wide. Further, I discovered that the most prominent feature is a shelf that shows up below M32, such that the companion galaxy appears to float on an ocean of faint gray-white nebulosity.
Familiar with the astonishing images by Steve Mandel and Rogelio Berlal Andreo of galactic cirrus that Steve calls the Integrated Flux Nebula, or IFN, I find myself contemplating the unthinkable. Could I see some portion of the IFN? The IFN next to M81 and M82 is bright and well imaged, so I have an idea of what to expect. I select my 10.5 inch F2.7 Richest Field Telescope, aim the red dot finder at the area of M81 and M82 as I have so many times over the decades and place my eye at the eyepiece. Holy cow! Not only can I see it but it is bright. My elation is unbounded. Am I the first to observe and sketch the IFN? I sketch the ‘Angel Integrated Flux Nebula’, an area not associated with an object. Beautiful, bright, subtle, deeply gratifying – an observation I will never forget. The sky is filled with IFN, awash in faint cirrus with surprising detail.
Hershel and others talked about noticing that 'this field' is ever so slightly brighter than 'some other field'; in other words, they didn't see structure or form. The IFN next to M81, M82 according to Sandage has brightness of 24.5 mag/arcsec^2. I estimate the faintest portions visible are in 25.5 mag/arcsec^2, or a contrast of a scant several percent, taking into account good nights with SQM reading of the sky background at 21.4 mag/arcsec^2.
The Milky Way extension that reaches M33 the Triangulum Galaxy is surprisingly bright. How could I have missed it all these years? Serendipitously, I find galactic cirrus in the fields of the globular cluster M15, the Beehive cluster M44, the Leo Triplet of galaxies (M65, M66, NGC 3628) and the Virgo Cluster of Galaxies, Markarian’s Chain. I am tuned to subtle variations in background brightness from sketching 243 dark nebulae; nebulae that fascinate me not only in their beauty through the eyepiece but also the history of their discovery and gradual understanding that they are not holes in the sky.
What is galactic cirrus? Faint streamers of gas and dust extend far above and below the galactic plane all the way to the galactic pole. The gas and dust reflects blue light from the glow of countless millions of Milky Way stars and the dust glows dimly in red light.
Steve Mandel noticing the glow associated with M81 and M82 began imaging the clouds as his Unexplored Nebula Project (UNP) in 2004. It is his images that I use to explore the IFN visually. Steve Mandel was awarded The Chambliss Award for Amateur Achievement for 2008 for his achievements.
The discovery story you’ll read goes something like this. Galactic cirrus was first noticed on glass plates using the Schmidt telescope at Palomar Observatory, one of the most productive telescopes of the modern age. Cataloged by B. T. Lynds, in 1965, their infrared properties were discovered in the early 1970’s and studied in detail by IRAS, the Infrared Astronomical Satellite. David Malin also found cirrus on images from the UK Schmidt telescope at Siding Spring Observatory, Australia. Allan Sandage wrote about the nebula in 1976.
The discovery story you won’t read is quite interesting and goes back another 150 years to perhaps the greatest visual astronomer of all time, William Herschel. He became aware of very faint nebulosity affecting large areas of the sky. What we call the sky background he called the sky’s ‘bottom’. From 1783 to 1811 he cataloged 52 nebulous regions including the Horsehead Nebula in 1786 (the discovery is commonly attributed to Williamina Fleming in 1888, one of Edward Pickering’s human computers and popularized by Edward Barnard’s astrophotographs in 1884). Herschel‘s observations also point to the North American Nebula and Barnard’s Loop plus the IFN associated with M81 and M82.
Herschel initially believed that astronomical objects were resolvable, that is, nebulosity could be explained by aggregations of stars too faint to be seen individually, so he did not judge differences in sky ‘ground’ important – after all, there were no stars to be counted. So his catalog of 52 diffuse nebulae never made it into his well-known catalogs. Eventually Herschel came to believe that nebulous material was very common. He published his catalog of extensive diffused nebulosities in 1811, at the end of his career. However, neither his son John Herschel, nor John Dreyer (New General Catalog), chose to include Herschel’s nebulosities in their catalogs. Thus Herschel’s diffuse areas became historical and observational ghosts.
These ghostly nebulous regions did not interest astronomers of the day. Herschel acknowledged that they “can only be seen when the air is perfectly clear, and when the observer had been in the dark long enough for the eye to recover from the impression of having been in the light.” These regions are difficult to see, and frankly, there were no telescopes equal to his for nearly a century.
The British amateur Thomas Backhouse in 1891 took up the cause of observing Hershel’s diffuse nebulae. His judgment was that while he could see wispy clouds, they largely didn’t coincide with Hershel’s regions. In 1986 Isaac Roberts began systematically photographing Herschel’s 52 nebulous regions, using an exposure time of 90 minutes. The result was vastly negative: only four regions showed any hints of nebulosity. Roberts concluded that Herschel observations were illusions. Reaction was harsh: Max Wolf and Edward Barnard criticized Roberts saying that 90 minutes was not long enough (Barnard had photographed some of Herschel’s regions that we now call Barnard’s Loop, nebulosity that Roberts claimed did not exist).
Herschel’s observations were next taken up by the Austrian American Jesuit astronomer, Johann Hagen, Directory of the Vatican Observatory in Rome. He began systematically visually surveying the sky for so called ‘cosmic clouds’ using the 6 inch F15 refractor. He eventually claimed to have observed all 52 of Herschel’s nebulae; results that met with derision because his clouds were not photographically detectable. Hagen continued to compile his faint clouds up until his death, coming to believe that faint clouds cover much of the night sky. Hagen was a true visual observer, favoring the visual record over photographs, saying that many hours of long exposures couldn’t match watch he could see in minutes. He advised astronomers to put away their cameras and look through the telescope, lamenting that visual skills were a dying art.
The French amateur Marcel de Kérolyr, one of the greatest astrophotographers of all time, well known violinist, whose home the American dancer Isadora Duncan left only to suffer her fatal accident, but unknown today, became involved, successfully photographing some of Herschel objects and publishing visual observations of most of them.
Curiously, Robert’s widow, the leading French astronomer Dorothea Klumpke Roberts, collaborated with Hagen, perhaps to resuscitate her husband’s reputation, which had suffered with his harsh criticism of Herschel. Her photographs received attention and applause, even Edward Hubble, a sharp critic of Hagan, in a turnabout, suggested more photographs. With Hagen’s death in 1930, interest in Herschel’s and Hagen’s observations ceased. The astronomical world lost this fascinating thread reaching back to Herschel, one of humanity’s greatest visual observers.
Perhaps the illusive nature of these ephemeral nebulae and their forgotten observations will capture your interest in imaging and sketching Herschel’s ghosts. It’s captured mine.
Andreo, Rogelio Bernal, RBA Premium Astrophotography. http://www.deepskycolors.com/
Bartels, Mel, Observing Dark Nebulae. http://www.bbastrodesigns.com/dneb/Observing Dark Nebulae.html
GaBany, R.J., Integrated Flux Nebulae Surround Our Galaxy. http://www.cosmotography.com/images/gal ... irrus.html
Hommage a Mercel Bonnemain de Kerolyr, https://www.youtube.com/watch?v=UGGPi0WtEbY (2015)
Hughes, Stephen, Catchers of the Light, the Forgotten Lives of the Men and Women Who First Photographed the Heavens (2015)
Latussek , Arndt, William Herschel’s Fifty-Two Fields of Extensive Diffused Nebulosity – A Revision. Journal of Astronomical History and Heritage, 11(3), 235-246 (2008)
Mandel-Wilson, Unexplored Nebulae Project. http://www.galaxyimages.com/UNP1.html (2005)
Mörka obsplatser, beskrivningar etc.
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Man behöver inte ens teleskop utan det räcker med blotta ögonen. Ljusgrejen mellan det Stora Magellanska Molnet och vår vintergata i Triangulum Australe misstänker jag kan vara en Integrated Flux Nebula. Bara en handfull människor har sett ljuset med egna ögon. Varför studerar inte astronomerna fenomenet? Min sydafrikanske vän, Dana de Zoysa, studerar det. Han är den ende personen (vad jag vet) som bor på södra halvklotet som ser ljuset regelbundet från sin farm i Great Karoo. Det behövs i princip en SQM-L 22.0 himmel för att notera ljusbryggan. Hoppas han kan trigga igång forskningen om min LMC materiebrygga.
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