![Picture](/uploads/7/5/0/9/75097535/published/1084px-abell-ngc2218-hst-big.jpg?1635867245)
Abell 2218 is a cluster of galaxies about 2 billion light years away in the constellation as a powerful lens, its gravity magnifies and distorts all galaxies lying behind the cluster core into long arc. The lensed galaxies are all stretched along the cluster’s center and some of them are multiply imaged. Those multiple images usually appear as a pair of images with a third – generally fainter – counter image, as is the case for the very distant object. The lensed galaxies are particularly numerous, as we are looking in between two mass clumps, in a saddle region where the magnification action is quite large. I thought that it would be interesting to see if the RCOS RC-20 could see the arcs.
Abell 2218 was used as a gravitational lens to discover the most distant known object in the universe as of 2004. The object, a galaxy some 13 billion years old, is seen from earth as it would have been just 750 million years after the Big Bang.
The color of the lensed galaxies is a function of their distances and types. The orange arc is an elliptical galaxy at moderate redshift (z=0.7). The blue arc are star-forming galaxies at intermediate redshift (Z=1 – 2.5)
- Right Ascension: 16h 35m 54s: Declination: +66d 13m 00s
- Constellation: Draco
- Number of galaxies: approx. 10,000
- Distance: 2,345 Mly
- Date: July – August 2014
- Exposure: Lum 7 hours, Red 3.0 hours, Geen 4.0 hours, Blue 3.0 hrs
- Instrument: RCOS 20 inch at f8.2 (fl=4116mm), SBIG ST8-XME (1 pixel=0.4509 arc-sec)
- Processing: MaxIm DL & Photoshop