NGC 2371 and NGC 2372: This is a small (about 2.6 arcminutes across the semi-major axis; about three times the angular size as Jupiter at its closest to earth) planetary nebula in the constellation Gemini. It is not very bright (overall magnitude of about 13), but the central part is bright enough to be seen through a 6" telescope); the wide dynamic range of the object makes it a bit of a challenge to process.

It oddly carries two entries in the NGC catalog, NGC 2371 and NGC 2372, probably because, visually, it seems to be two separate objects.

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 estimated to be approximately 4400 light years from earth, which would give it a diameter of about 3 light years.

Technical Information:

(L)(R+Ha)(G+OIII)(B+OIII): Ha-780, OIII-570, L-555, R-240, G-180, B-240 (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 26 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.

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 STX guider, 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 2025 and January and February of 2026. Image posted August 2, 2026.

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

Seeing: Highly variable, most often poor

CCD Chip temperature: -25C

Copyright 2025, 2026 Mark de Regt

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