NGC 7331 and Stephan's Quintet

Object Information:

NGC 7331:

NGC 7331 (also known as Caldwell 30) is a unbarred spiral galaxy about 40 million light-years (12 Mpc) away in the constellation Pegasus. It was discovered by William Herschel in 1784. NGC 7331 is the brightest member of the NGC 7331 Group of galaxies. The other members of the group, visible to the left of NGC 7331 in the main image, are lenticular or unbarred spirals NGC 7335 and 7336, barred spiral galaxy NGC 7337 and elliptical galaxy NGC 7340. These galaxies lie at distances of approximately 332, 365, 348 and 294 million light years, respectively. In both visible light and infrared photos of the NGC 7331, the core of the galaxy appears to be slightly off-center, with one side of the disk appearing to extend further away from the core than the opposite side.

The galaxy is similar in size and structure to the galaxy we inhabit, and is often referred to as "the Milky Way's twin", although recent discoveries regarding the structure of the Milky Way may call this similarity into doubt, particularly because the Milky Way is believed to be a barred spiral, compared to the unbarred status of NGC 7331.

Stephan's Quintet:

Stephan's Quintet in the constellation Pegasus is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered. The group was discovered by Édouard Stephan in 1877 at Marseille Observatory. The group is the most studied of all the compact galaxy groups. The brightest member of the visual grouping is NGC 7320 that is shown to have extensive H II regions, identified as red blobs, where active star formation is occurring.

These galaxies are of interest because of their violent collisions. Four of the five galaxies in Stephan's Quintetform a physical association, Hickson Compact Group 92, and are involved in a cosmic dance that most likely will end with the galaxies merging. Radio observations in the early 1970s revealed a mysterious filament of emission which lies in inter-galactic space between the galaxies in the group. This same region is also detected in the faint glow of ionized atomic hydrogen seen in the visible part of the spectrum as the magnificent green arc in the picture to the right. Two space telescopes have recently provided new insight into the nature of the strange filament, which is now believed to be a giant intergalactic shock-wave (similar to a sonic boom but traveling in intergalactic gas rather than air) caused by one galaxy (NGC 7318B) falling into the center of the group at several millions of miles per hour.


Exposure Information: 6h40 minutes exposure

Lights: 40x600" 1600ISO
Darks: 19
Flats: 30
Bias: 50

Temperature 19ºC
Moon phase 13%
Imaged at: Prades, Tarragona, CATALUNYA - SPAIN

Optics - GSO- 200/1000 Newtonian f/5
Camera - Canon 450D moded (IR filter removed)
Mount - Sky-Watcher Neq6 PROII
Guiding scope – EZG 60/230
Guiding and planetary camera – ASI 174MC

Software: APT, PHD2, DSS, PIX

Image date: August 6th and 7th, 2016