Focal Pointe Observatory
Astrophotography by Bob Franke

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ARP 31 and Friends


Click the image for a higher resolution view. (2100 x 1400 - 1.12 MB)


12.5" RCOS @  ~f/9 (2880 mm fl) at 0.64 arcsec/pixel. Shown at 2.77 and 0.99 arcsec/pixel.


Paramount ME


SBIG STL-11000 w/ FW8 filter wheel, AstroDon Gen-2 Filters

Acquisition Data

10/21/2014 to 11/27/2014 Chino Valley, AZ... with CCDAutoPilot, CCD Commander & CCDSoft, AOL guided.



360 min. (24 x 15 min.)   Bin 1x1


810 min. (18 x 15 min. each)  Bin 2x2

Software & Processing Notes

  • CCDSoft, CCDStack, PixInsight & Photoshop CS6.

  • eXcalibrator v4.25 for (g:r) color balancing, using 50 stars from the SDSS-DR9 database.

  • CCDBand-Aid to repair KAI-11000M vertical bars.

  • CCDStack to calibrate the sub exposures.

  • PixInsight processing includes sub exposure registration and stacking, RGB creation, gradient repair and non-linear stretching with HistogramTransformation.  Selective use of HDRMultiscaleTransform, with various layer counts, was used to individually enhance the detail of the four galaxies.

  • PhotoShop for combining the images with varying galaxy detail, creating the LRGB and final touch up.


The image is shown with north to the top.

This field of view, in the constellation Aries, is a great example of galaxy diversity. From left to right, the galaxies are ARP 31, NGC 691, NGC 680 and NGC 678. Their respective distances from Earth are 118, 106, 118 and 113 million light years.

ARP 31 is in an irregular barred spiral galaxy with only two arms. NGC 691 is a smoother than normal face on Sc spiral galaxy. NGC 680 is an asymmetrical elliptical that also shows the characteristics of a shell galaxy. Deeper exposures revealed two tidal tales with one extending towards the nearby galaxy, NGC 678. This suggests that the two are an interacting pair. Finally, NGC 678 is an edge view of an SBb spiral galaxy with an interesting dust lane.