Abell 773 and Abell 782 are two distant galaxy clusters in the constellation Ursa Major not far in RA/Dec from the bright galaxy NGC 2841.  The “final” revision shows Abell 773, the “B” revision shows Abell 782, and the “C” revision shows their positions relative to one another with a wider field of view.

Abell 773 is presently thought to have a redshift of z=0.22,[1] placing it at about 930 Mpc or 3 billion light years if one assumes H0 = 70.8 km/s/Mpc.  It was placed in Abell richness class 2 (80-129 members) and distance group 6 (out of 7), and is listed as having 108 members. [2]  Abell 773 has attracted attention due to gravitational lensing of an “exceptionally bright,” distant background galaxy with z = 5.2429. [3] The overall visual magnitude of the entire cluster was estimated to be 17.5 in the 1989 Abell catalogue paper. [2] 

There is less published information available regarding Abell 782, which has 107 members and an overall visual magnitude of 17.4. [2]  It was also placed in distance group 6 by Abell et al. [2]

While it seems rather inappropriate to use a little 100 mm refractor to image some of the more distant Abell galaxy clusters, I was able to capture images of these seldom-seen deep sky objects as a “free bonus” at the edge of the field of view after spending 19 hours on NGC 2841.  I stretched the image to nosebleed levels and applied minimal noise reduction, so you’ll have to excuse the grainy images until I get myself a 1 m 'scope on the top of a mountain in New Mexico.  The image captured objects down to magnitude 21.9 according to analysis performed in ASTAP.

Some of the stars in this image have a hexagonal shape that is due to the slightly pinched optics in my Esprit 100ED.  I just have to accept the hexagons in cold weather and keep telling myself that these artifacts are no worse than diffraction spikes.

References

1.  Barrena, R., Boschin, W., Girardi, M. and Spolaor, M., 2007. Internal dynamics of the radio halo cluster Abell 773: a multiwavelength analysis. Astronomy & Astrophysics, 467(1), pp.37-48.

2.  Abell, G.O., Corwin Jr, H.G. and Olowin, R.P., 1989. A catalog of rich clusters of galaxies. Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 70, May 1989, p. 1-138., 70, pp.1-138.

3.  Pérez González, P.G., 2012. A bright z= 5.2 lensed submillimeter galaxy in the field of Abell 773 HLSJ091828. 6+ 514223.