In 1704 Isaac Newton wondered if the force of gravity would deflect "light corpuscles". Albert Einstein calculated the amount of this deflection in 1915 and he speculated that multiple images of a distant object might be seen as light passed around a star closer to us, but he thought that this would be a very unlikely occurrence. In 1937 Fritz Zwicky suggested that a cluster of galaxies might be massive enough to make this phenomenon more likely. Such a gravitational lens was discovered in 1979 when two identical appearing quasars were seen (SBS 0957+561). Since then hundreds of gravitational lenses or Einstein rings have been identified.
LRG3-757, also called the Cosmic Horseshoe, was discovered in 2007. The foreground galaxy (LRG stands for luminous red galaxy, a type of very massive galaxy with high infrared emission) is 5.6 Gly away and the background lensed galaxy is 18.9 Gly away. HST image below:
So, I wondered if it would be possible for me to image this. LRG3-757 is visible in my 5h 42m LRGB exposure. It is a magnitude 20.3 target. This image was made with a 5-inch refractor, in a Bortle 6 sky, with my neighbor's new LED flood light shining on me (I blocked it with a piece of cardboard). The first inset is magnified 2x. The second inset is magnified about 8x. The target has a different appearance from other dim stars with some contour complexity and maybe a few red and blue pixels.
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