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I agreeImaging telescope or lens:9" MK "Santel"
Imaging camera:QSI 640i
Mount:Sky-Watcher EQ8
Filters:Baader L , Baader RGB Filters
Accessories:Starlight Xpress Lodestar, Starlight Xpress Off Axis Guider, Starlight Xpress Fliter Wheel
Resolution: 1957x1963
Dates:April 16, 2018, April 25, 2019, April 27, 2019, May 3, 2019, May 27, 2019, May 29, 2019, May 30, 2019, June 4, 2019, June 6, 2019, June 25, 2019, June 27, 2019, July 2, 2019, July 6, 2019
Frames:
Baader L : 57x1800" bin 1x1
Baader RGB Filters: 87x600" bin 2x2
Integration: 43.0 hours
Avg. Moon age: 17.64 days
Avg. Moon phase: 23.45%
Bortle Dark-Sky Scale: 2.82
Mean SQM: 21.65
Astrometry.net job: 2810723
RA center: 248.990 degrees
DEC center: 66.218 degrees
Pixel scale: 0.512 arcsec/pixel
Orientation: 0.861 degrees
Field radius: 0.197 degrees
Data source: Traveller
Abell 2218 galactic cluster in the constellation Dragon, is about 2.1 billion light years from Earth (cosmological redshift z = 0.17).
The photo shows a set of small yellowish galaxies. For a particular identification of details is very helpful here is this work:
http://iopscience.iop.org/article/10.1086/177995/pdf
No. 289. The brightest and most easily detectable arc. z = 1.03. Visible even on some individual subs.
No. 359 /328. The first is a brighter and more easily detectable red arc, the second is a weaker counter-image of the first arc 359. z = 0.7. The complex itself (plus no. 337/389 visible in the HST image), according to scientists, is an image of a background spheroidal galaxy.
No. 384 /468. The first is still bright, the second is very weak counter-image of the first arc. z = 2.8. The value of the redshift is such that the object will move away from us at a speed of 261,000 km/s, which is already 87 % of the speed of light.
No. 444. Much weaker than its neighbour arc 384. z = 1.1. Magnitude in red 23m.
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