Pictured here passing between Hercules and Bootes is a green comet. It last appeared near Earth 50,000 years ago. I wonder if the Neanderthals noticed it? This was just visible to the naked eye when I took the image. Comets are made of ice, gas and dust which get released in a visible tail.

1hr 51mins total exposure, using LRGB filters with 60" exposures and an additional set for the stars in its field of view.