IC 239 is a barred spiral galaxy, about 35 million light years from us, presenting to us almost fully face-on. At that distance, it is only about 50,000 light years in diameter, small for a spiral galaxy. It is extremely dim, along with being small and positioned in our sky close to some very bright stars, making it a challenge to image effectively.

I always enjoy looking at the small background galaxies in many of my images; there are many throughout the uncropped image. Perhaps most priminent among them is PGC 2802360, the smudge above the bright yellow/orange star to the right of IC 239 (in the uncropped images). There are a number of bright, blue stars in the upper part of the uncropped images, highlighted by the mag 5.91 star to the left of center at the top. Like all the individual stars in the image, the stars in the immediate vicinity of the galaxy in my image are foreground stars, in our own galaxy. The brightest is the yellow/orange star just above and to the left of the galaxy, at mag 8.6 (very bright for a long exposure).

The entire field of the uncropped version of the photo is about the same width as a full moon.

Technical Information:

(HaL)(HaR)(G)(B): Ha:L:R:G:B: 660:540:180:180:260 (a total of ovr 30 hours of light-frame exposure time); here's a chart showing the various subexposures I used in the image:

Hydrogen Alpha: 22 twenty-minute
Luminance: 24 twenty-minute (14 of the 38 I kept were discarded during processing), and 20 three-minute
Red: 12 fifteen-minute
Green: 12 fifteen-minute
Blue: 13 twenty-minute
The luminance layer is a mix of the luminance-filtered images and the Ha-filtered images; the red channel is a mix of the red-filtered images and the Ha-filtered images; the green channel is only green- filtered images; the blue channel is only the blue-filtered images.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chrétien 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, Noise XTerminater, Blur XTerminator) 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 during October and November of 2025. Image posted February 27, 2026.

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

Seeing: Variable, but generally ok.

CCD Chip temperature: -25C

Copyright 2025, 2026 Mark de Regt

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