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Arp 20, 


            Gary Imm

Arp 20

Getting plate-solving status, please wait...
Arp 20, 


            Gary Imm

Arp 20

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

Dates:Jan. 15, 2021Jan. 16, 2021

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

Integration: 5.0 hours

Avg. Moon age: 2.87 days

Avg. Moon phase: 9.25%

Basic astrometry details job: 4240936

Resolution: 2150x1762

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

Data source: Backyard


This Astrobin Debut Object is a disturbed spiral galaxy located 200 million light years away in the constellation of Taurus at a declination of +2 degrees. This 14.4 magnitude galaxy spans 1 arc-minute in our apparent view and has a diameter of 70,000 light years.

This galaxy was classified by Dr. Arp into the category of Spiral Galaxies – Three Armed. The galaxy arms are clearly disturbed. But does this galaxy actually have 3 arms, as classified by Dr. Arp? It actually looks like 2 arms to me, with the “third arm” at upper right being an extension of the arm at left as it wraps around the galaxy.

When comparing this to other undisturbed barred galaxies, it looks like this one started as a barred galaxy with an arm extending from each end of the bar, and then became disturbed by a companion cutting across the bottom right of the galaxy. Is this companion still visible, or was this a "hit and run"? We are too far away to tell whether any of the bright regions in the disk is a small companion galaxy vs. a bright star forming cluster, although the bright blue area below the core looks different from the other regions and a bit suspicious to me.