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Observation by Dean Ashton: A one-armed galaxy

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Dean Ashton


Dean Ashton


2021 Apr 15 - 22:00


2021 Apr 17 - 09:51



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Coma Berenices

Field centre

RA: 12h50m
Dec: +25°29'
Position angle: +0°58'

Field size

0°33' × 0°21'

  • Celestron 9.25 EdgeHD
  • QHY268C Camera
  • Celestron CGEM Mount
  • Optolong L-Pro Filter

54x600 light frames; /f10; focal length 2,350mm, Camera High Gain Mode, Gain-56


St Austell, Cornwall

Target name



A one-armed galaxy

About this image

NGC4725 in Coma Bernices is clearly a barred spiral galaxy.  Very unusually though, it has a single spiral arm.  A large galaxy, 111,000 light years in diameter and 39 million light years distant, it presents with a good 10x7 arc minutes size in the sky.

Also in the image is NGC4712 that is larger with a diameter of 130,000 light years, but is 288 million light years away from us.

A total of 9-hours integration taken as 54x600s light frames on the 11th, 12th and 15th April 2021.

Camera TEC at -25C.  100x flat frames taken on the night.  Camera sensor overscan area used to correct for bias drift in the IMX571 sensor; camera sensor dark-black area used to calibrate for dark/thermal current.

Image capture and telescope control with SGP.

All calibration and processing with PixInsight.

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