Abell 78 is a small, fairly bright planetary nebula, visually located in the constellation Cygnus.

This pretty nebula is thought to be about 2800 light years from us, and covers about 2 arcminutes of the sky; at that distance, the nebula is about 1.6 light years across.

The blue-green is the emission from doubly-ionized oxygen atoms; red is the emission from ionized hydrogen atoms. The purple is where there are both OIII emissions and Ha emissions.

There are about thousands of stars in the uncropped field, which is slightly larger than a full moon; there are a lot of stars in the sky that we don't see!

I have photographed this nebula once before, 19 years earlier. To see the benefit of better equipment; better software; better location and better skills, click here

Technical Information:

(HaOIIIL)(HaR)(OIIIG)(OIIIB): Ha:OIII:L:R:G:B: 600:630:582:180:165:240 (a total of almost 40 hours of light-frame exposure time); here's a chart showing the various subexposures I used in the image:

Hydrogen Alpha: 20 thirty-minute
Oxygen III: 21 thirty-minute
Luminance: 34 fifteen-minute, and 24 three-minute
Red: 12 fifteen-minute
Green: 11 fifteen-minute
Blue: 12 twenty-minute

The luminance layer is a mix of the luminance-filtered images, the Ha-filtered images and the OIII-filtered images; the red channel is a mix of the red-filtered images and the Ha-filtered images; the green channel is a mix of the green-filtered images and the OIII-filtered images; the blue channel is a mix of the blue-filtered images and the OIII-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 (using NormalizeScaleGradient) in Pixinsight. Color combine in Pixinsight. Narrow-band data blended into the luminance and color layers in Pixinsight. Some finish work (gradient correction, background neutralization, color calibration, NoiseXTerminator, BlurXTerminator, done in Pixinsight; some finish work (LRGB combination, 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 September and October of 2025. Image posted January 26, 2026.

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

Seeing: Variable; often good, but often not at all good.

CCD Chip temperature: -25C

Copyright 2025, 2026 Mark de Regt

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