NGC 2392: This is a very small (about 50 arcseconds across; the same angular size as Jupiter at its closest to earth) planetary nebula in the constellation Gemini; although of modest visual magnitude (9.1), its tiny size results in a very high surface brightness, making it a serious challenge to process. A "planetary nebula" (so called because the astronomer who first identified them as nebulae noted the color 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; there also is some ionized hydrogen, which shows a reddish color). It is called the "Eskimo Nebula," because of the resemblance of a person wearing a fur-lined hood. It is estimated to be approximately 4200 light years from earth, which would give it a diameter of about 1 light year.

Technical Information:

(L)(R+Ha)(G+OIII)(B+OIII): Ha-750, OIII-600, L-60, R-225, G-225, B-260 (Luminance layer was a composite of 20 three-minute, luminance-filtered images; Red channel was a blend of 15 fifteen minute red-filtered images and 25 thirty-minute Ha-filtered images; Green channel a blend of 15 fifteen-minute green-filtered images and 20 thirty-minute OIII-filtered images, and the blue channes was a blend of 13 twenty-minute blue-filtered images and the OIII data. All images unbinned. I also took 45 fifteen-minute images through the luminance filter, but did not use any of those, since they resulted in the nebula being too bright.

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 and BlurXTerminator, blending in the narrow-band data) done in Pixinsight; some finish work (LRGB combination, contrast 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 December 2023 and January, February, April, October and November of 2024. Image posted June 13, 2025.

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

Seeing: Highly variable

CCD Chip temperature: -25C

Copyright 2023, 2024, 2025 Mark de Regt

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