This spooky Halloween-themed image from the NASA/ESA Hubble Space Telescope, resembles fog lit by a streetlamp and a curiously shaped ‘hole in space’. When the dark patch was first seen, it was assumed to be a very cold, dense cloud of gas and dust, totally opaque in visible light and blocking all light behind it. But thanks to ESA’s Herschel space telescope, which looked for any hints of star formation at infrared wavelengths, it turned out to be a truly empty patch of sky. See http://www.esa.int/spaceinimages/Images/2017/10/Reflection_nebula_NGC_1999
