... Mariner's Mercury . ... Mercury, the closest planet to the Sun, remains the most mysterious of the Solar System's inner planets. ... Nebula Nova Cygni Turns On . ... Light flooded the local interstellar neighborhood, illuminated this existing gas cloud, excited the existing hydrogen, and hence caused the red emission. ... Here a very distant QSO happened to be placed right behind a massive galaxy. ... A typical place is an area of dense nebular gas common to arms in spiral galaxies. ...