Hemisphere:  Northern  ·  Constellation: Ursa Major (UMa)  ·  Contains:  NGC 5278  ·  NGC 5279  ·  NGC5278  ·  NGC5279
Getting plate-solving status, please wait...
Arp 239, 


            Gary Imm
Arp 239, 


            Gary Imm

Arp 239

Getting plate-solving status, please wait...
Arp 239, 


            Gary Imm
Arp 239, 


            Gary Imm

Arp 239

Imaging telescopes or lenses: Celestron EdgeHD 11

Imaging cameras: ZWO ASI 294 MM Pro

Mounts: Astro-Physics Mach1GTO

Guiding cameras: ZWO ASI 174 MM Mini

Software: Main Sequence Software Sequence Generator Pro  ·  Pixinsight  ·  Stark Labs PHD2 2.6.3

Filters: Astrodon Green 31mm Gen2 I-Series  ·  Astrodon Blue 31mm Gen2 I-Series  ·  Astrodon Lum 31mm Gen2 I-Series  ·  Astrodon Red 31mm Gen2 I-Series

Accessory: Celestron OAG  ·  ZWO EFW 2″X7  ·  MoonLite Focuser for EdgeHD 11

Dates:March 3, 2021March 4, 2021

Astrodon Blue 31mm Gen2 I-Series: 30x120" (1h) (gain: 120.00) -20C bin 2x2
Astrodon Green 31mm Gen2 I-Series: 30x120" (1h) (gain: 120.00) -20C bin 2x2
Astrodon Lum 31mm Gen2 I-Series: 60x120" (2h) (gain: 120.00) -20C bin 2x2
Astrodon Red 31mm Gen2 I-Series: 30x120" (1h) (gain: 120.00) -20C bin 2x2

Integration: 5h

Avg. Moon age: 19.91 days

Avg. Moon phase: 72.80%

Astrometry.net job: 4275898

RA center: 13h 41' 41"

DEC center: +55° 40' 21"

Pixel scale: 0.343 arcsec/pixel

Orientation: -0.112 degrees

Field radius: 0.118 degrees

Resolution: 1896x1606

Locations: Backyard (Mag 20.8 - Bortle 4.5), Onalaska, Texas, United States

Data source: Backyard


This object is a pair of interacting spiral galaxies located 375 million light years away in the constellation of Ursa Major at a declination of +56 degrees. The data shows them to be about 2 million light years apart, but that data has a range of uncertainty larger than that. NGC 5279 is on the left and NGC 5278 is on the right.

This object was classified by Dr. Arp into the quizzical category of Galaxies – Appearance of Fission. Its appearance has been described as similar to M51, although I find the galaxies of M51 to be more superimposed than interacting.

The smaller magnitude 15.0 galaxy on the left spans 30 arc-seconds in our apparent view and has a diameter of 50,000 light years. The brighter 13.6 magnitude galaxy is about twice as large.

The top arm of each galaxy is the “strong” arm. To me, they seem to be clearly interacting. The two strong arms are connected by a beautiful star stream bridge. I have included this object in my Stellar Bridges Collection.

Distortion is seen in the asymmetric arms of each galaxy. For the smaller galaxy, the top arm is much longer than the bottom. For the larger galaxy, the distortion is so severe that it appears to have only one arm.

We are fortunate to have a face-on viewing perspective of this object. Can you imagine what it would look like if our view was from the side?

The galaxy further to the right (MCG+09-22-094) is 540 million light years away and obviously not interacting with the pair. The galaxy to the lower right (UGC 8671) is 350 million light years away and could have interacted with this pair in the past.