NGC 1931
NGC 1931
Emission and Reflection Nebula in Auriga

Click here for higher-resolution, uncropped versions:  40% (1606x1614)  65% (2610x2623) 100% (4016x4036)


NGC 1931 is a small nebula containing both emission components (the reddish stuff) and reflection components (the blueish stuff). As is the case with most emission nebulae, NGC 1931 is a star-forming region. The emission nebula is very predominantly red, because (i) ionized hydrogen emits in the red part of the spectrum; (ii) the vast majority of the matter in the universe is hydrogen, and (iii) the hydrogen is being ionized (stripped of its electron) by a highly-energetic young star in the center of the nebula.

NGC 1931 is about 7,000 light years away from Earth, and has an apparent diameter of about 6 arcminutes (1/5 of the diameter of the full moon), giving it an actual diameter of about 12 light years.

This object reminds me a lot of the Cocoon Nebula.

If you look at the uncrooped version, you will see lots of faint nebulosity/dust in the image.


Technical Information:

Ha:L:R:G:B: 630:780:255:180:180 (a total of almost 34 hours of light-frame exposure time); luminance, red and green exposures were all 15-minute exposures; blue all 20-minute exposures; Ha were all 30-minute exposures. I took lots of OIII data, but it would not have added anything, so I didn't use it. The luminance layer consisted of a blend of: (i) 36 fifteen-minute images through the luminance filter, (ii) 48 five-minute images through the luminance filter, and (iii) 21 thirty-minute images through the Ha filter. The red channel is a blend of the red-filtered data and the Ha-filtered data.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chretien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 camera with internal filter wheel (SBIG filter set), guided by an SBIG AO-X, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X.

Processing: All images calibrated (darks, bias and sky flats), aligned, combined and cropped in Pixinsight. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, NB blend, deconvolution, multiscale linear transform, HDR multiscale transform, and noise reduction) done in Pixinsight; some cleanup finish work was done in Photoshop CC.

Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights in February, March and April of 2022. Image posted June 2, 2022.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally good; luminance images varied in FWHM from 1.7 to 2.8 arcseconds; luminance master was deconvolved to 1.5 arcsecond FWHM.

CCD Chip temperature: -25C

Copyright 2019, 2020 Mark de Regt

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