There are many galaxies in the Universe, and sometimes two of them will come close enough to start interact between them. But it may be more than two, and that is the case of Hickson 92 galaxy group also known as Stephan’s Quintet. In the small area of the sky there are five visible small galaxies, but only four of them are actually interacting. NGC7320 – the one with blueish outskirts – is actually much closer to us. Distance to other four is about 250 million light years.

Stephan's Quintet compact galaxy group
Stephan’s Quintet compact galaxy group

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Stephan’s Quintet is first compact galaxy group ever discovered. It happened in 1877 at the Marseille Observatory, and Édouard Stephan was the discoverer. It is clearly visible, that galaxies form physical association – they are distorted, and also long tidal tail is visible. Scientists believe, that small galaxy NGC7320C (PGC69279) seen to the left of the main group also belongs to Hickson 92. It has similar redshift, and tidal tail seems to connect it with NGC7319.

Arp 319 annotated image
Annotated image

I have collected subframes to this image over one September night at my suburban backyard. Conditions were decent – good transparency and good seeing, but due to incoming clouds the total amount of data is not large. But still some details of the group were recorded, and tidal tail as well 🙂

Stephan's Quintet galaxy group - inverted luminance channel
Stephan’s Quintet galaxy group – inverted luminance channel

Large version

Clear skies!

Image technical data:

Date:       4 September, 2019
Location:   Nieborowice, Poland
Telescope:  Meade ACF 10"
Corrector:  AP CCDT67
Camera:     QHY163M, gain 100
Mount:      SW EQ6
Guiding:    SW 80/400 + ASI290MM
Exposure:   L 120x2 minutes, RGB 50:30:40 x 1 minute
Conditions: seeing good, transparency good