Imagine taking a picture of a scene that required a long exposure that strayed into hours, say 50 days (or a total exposure of 2 million seconds). Fortunately, it was not one long exposure but more than 2,000 images taken over the course of 10 years, staring at the same tiny patch of southern sky. The eXtreme Deep Field (XDF) contains about 5,500 galaxies with the faintest galaxies at about one ten-billionth the brightness of what the human eye can see.
“The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen. XDF allows us to explore further back in time than ever before”
Read the article at: NASA.