Herschel's Ghosts

by Mel Bartels

Visual discovery of the Integrated Flux Nebulae (galactic cirrus) and InterStellar Medium (ISM)

The task isn't to see what's never been seen before, it is instead to think about what nobody has yet thought about that which everyone sees (adapted from Erwin Schrodinger).

“Nothing ever becomes real ‘til it is experienced.” - John Keats

Check out my article in the April issue of Sky and Telescope Magazine, "Herschel's Ghosts". I share my visual discovery of Integrated Flux Nebulae and my investigation into little known observations of earlier visual observers extending all the way back to William Herschel.

See Integrated Flux Nebulae in a small telescope? Impossible! Surely it is imagination or extraneous light or Zodiacal Light. That's what I thought until first light in my 6 inch [15cm] F2.8 Richest Field Telescope in 2013. After convincing myself that the Pleiades Bubble and Andromeda Shelf were aspects of the Milky Way and not extraneous light or Zodiacal Light (the Zodiacal Light is very broad, very gradually brightening and devoid of detail), I presumed that the faint patches of light I was seeing were part of the ISM (InterStellar Medium). One night I tried the impossible, to see and sketch an IFN. To my utter surprise, the IFN in the M81/82 was bright and detailed. I embarked on researching and discovering more IFN and ISM. My total is up to 52; I expect that to triple or quadruple by the time I've surveyed the skies visible from 44 degrees north latitude.

Dust and gas in the plane or disk of the Milky Way that resides between the stars is called the InterStellar Medium (ISM). Faint streamers of gas and dust that extend far above and below the galactic plane all the way to the galactic pole is called galactic cirrus or Integrated Flux Nebulae, since the dust glows dimly from the integrated light of countless millions of Milky Way stars.

I'm creating a catalog of my visual IFN and ISM discoveries that includes sketches and descriptions - everything you need to see these faint glows for yourself except the dark skies!

Here is the PDF version
Here is the Excel version

Why am I able to see IFN and ISM? First because I look for them, secondly because my Richest Field Telescope design has higher luminance or etendue. Luminance or etendue is the flux or light throughput of an telescope, measured in aperture times area (cm^2deg^2). Think of my 6 inch [15cm] F2.8 with its 4.3 degree field at low power. It fills my eye's pupil with 6 inches of aperture across 100 degrees of apparent field. I can zoom in closer, magnifying dim objects to a greater extent, yet have room to fit the entire object into the field of view so that I can see its edges. All this combines to make detection much easier. IFN can be seen in common telescopes, but in many cases, their detection is more difficult. For more on luminance, see my telescope optimizer.

Want to track down IFN? Discover new IFN? Alan Sandage analyzed the brightest portions of the IFN to be 24.5 mag/arcsec^2. If you observe from 21.4 mag/arcsec^2 skies, then you have a 6% contrast ratio, sufficient to see the IFN and dimmer detail when magnified to fit a very wide angle apparent field eyepiece. My observations suggest that only the brightest portions of the IFN can be seen when the sky is at 21.2 mag/arcsec^2. IFN visibility depends critically on very dark, contrasty, transparent skies.

Arndt Latussek describes the fascinating history of personal discovery followed by community disbelief with William Herschel in the late 1700's, Father Johann Hagen, Director of the Vatican Observatory in the 1920's and Marcel de Kérolyr in the 1930's. Other observers include Hermann Goldschmitt who discovered the Pleiades Bubble in 1863 and Walter Scott Houston who mentioned the Pleiades Bubble in an early Sky and Telescope Gleanings article.

References

Andreo, Rogelio Bernal, RBA Premium Astrophotography. http://www.deepskycolors.com/
Bartels, Mel, Observing Dark Nebulae. http://www.bbastrodesigns.com/dneb/Observing Dark Nebulae.html
Bartels, Mel, Reflecting Telescope Optimizer Suite. http://www.bbastrodesigns.com/telescopeCriteriaCalc.html
GaBany, R.J., Integrated Flux Nebulae Surround Our Galaxy. http://www.cosmotography.com/images/galactic_cirrus.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)
Kato, Hisayoshi, Flickr stream, https://m.flickr.com/#/photos/hiroc/6754827529/
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) http://www.narit.or.th/en/files/2008JAHHvol11/2008JAHH...11..235L.pdf
Mandel-Wilson, Unexplored Nebulae Project. http://www.galaxyimages.com/UNP1.html (2005)
Microsoft, World Wide Telescope. http://www.worldwidetelescope.org/webclient/ (e.g., the Plank thermal map)
Plantureax, Serge, La Peur Du Noir,
http://plantureux.fr/wp-content/uploads/2013/10/20.05.2005-Afraid-of-the-Dark.pdf