Hemisphere:  Southern  ·  Constellation: Eridanus (Eri)
Getting plate-solving status, please wait...
Arp 187, 


            Gary Imm
Arp 187, 


            Gary Imm

Arp 187

Getting plate-solving status, please wait...
Arp 187, 


            Gary Imm
Arp 187, 


            Gary Imm

Arp 187

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:Feb. 19, 2021Feb. 20, 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: 7.58 days

Avg. Moon phase: 52.06%

Astrometry.net job: 4281777

RA center: 5h 4' 53"

DEC center: -10° 14' 54"

Pixel scale: 0.282 arcsec/pixel

Orientation: -3.158 degrees

Field radius: 0.146 degrees

Resolution: 2946x2305

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

Data source: Backyard


This Astrobin Debut Object is a deformed spiral galaxy located 560 million light years away in the constellation of Eridanus at a declination of -10 degrees. This magnitude 15.0 galaxy spans 1 arc-minute in our apparent view, which corresponds to a diameter of 145,000 light years. This galaxy was classified by Dr. Arp into the category of Galaxies with Narrow Filaments.

Dr. Arp produced 338 identical sized images for his catalog, all 115mm by 90mm in portrait. These images used a range of magnifications and 2 telescopes (200 inch and 48 inch). As a result, the corresponding field size on these images ranged from 68 arc-minutes for the Leo Triplet, all the way down to 2.2 arc-minutes for the 58 smallest Arp objects. Arp 187 is one of those 58 smallest objects.

Sometimes it is difficult for me to reconcile my image with the Arp image. In Arp’s image, a sharp white thin stream (“filament”) extends down from the object. In my image, faint wider star streams extend above and below the object. I don’t understand how the stream in Arp’s image could be so sharp and thin. I don’t recall seeing a star stream like that anywhere else.

In addition to the star streams, another sign of disturbance is the asymmetric strong arm which extends upwards for Arp 187.

What is causing the disturbance of Arp 187? There is a galaxy (LEDA 98046 that looks suspicious just to the right, but I could find no distance information on this galaxy. Like many of these DSOs, the mystery will remain.