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: 16h 35' 57"
DEC center: +66° 13' 4"
Pixel scale: 0.512 arcsec/pixel
Orientation: 0.861 degrees
Field radius: 0.197 degrees
Resolution: 1957x1963
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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