NGC 6804: This is a very small (about 66 arcseconds by 48 arcseconds) and dim (magnitude 12) planetary nebula in the constellation Aquila. A "planetary nebula" (so called because the astronomer who first identified them as nebulae noted the color often was similar to the then recently-discovered Neptune) is a structure of gas resulting from the death throes of a star about the size of our sun, when it runs out of fusable material; the color is the result of the gas being ionized by the remnant of the star, a white dwarf (ionized oxygen is the dominant emission in this planetary nebulae, giving off the characteristic blue-green color). It is estimated to be approximately 4200 light years from earth, which would give it a diameter of about 1.2 light years.

The image on this page is full resolution (it's really a tiny nebula). I like dense star fields, and this one meets that description. If you like dense star fields (contrary to the current practice of eliminating stars), click on the links to the uncropped images (there's also a link to a cropped version upsampled to twice full resolution). Interestingly, most of my uncropped images have lots of little background (much farther away) galaxies, but this one does not have any that I could find. I assume that this is because I was imaging into the plane of the Milky Way galaxy, and the light from very distant galaxies isn't going to get through all that dust and all those stars.

Technical Information:

(L+OIII)(R+Ha)(G+OIII)(B+OIII): Ha-1080, OIII-1200, L-615, R-180, G-165, B-240 (a total of 58 hours of exposures that I used in the final photo; Luminance layer was a blend of 37 fifteen-minute and 20 three-minute luminance-filtered images, and 40 thirty-minute OIII_filtered images; Red channel was a blend of 12 fifteen minute red-filtered images and 36 thirty-minute Ha-filtered images; Green channel a blend of 11 fifteen-minute green-filtered images and the same OIII dated blended with the luminance layer, and the blue channes was a blend of 12 20-minute blue-filtered images and the OIII data. All images unbinned.

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 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, and combined in Pixinsight. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, gradient removal, NoiseXTerminator, BlurXTerminator) done in Pixinsight; some finish work (Smart Sharpening, LRGB combination and saturation adjustment) was done in Photoshop CC.

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

Date: Images taken on many nights in June and July of 2023. Image posted November 20, 2023.

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

Seeing: Generally good, with calibrated luminance images varying from 1.6 to 2.3 arcsecond FWHM

CCD Chip temperature: -25C

Copyright 2023 Mark de Regt

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