Astronomy Picture of the Day . A Rusty Sunset on Mars . ... The unusual color is partly due to rust: oxidized iron from Martian dust circulating in the Martian atmosphere. ... 15,000 years ago a star in the constellation of Cygnus exploded -- the shockwave from this supernova explosion is still expanding into interstellar space! ... The Cat's Eye Nebula . ... This image from the Hubble Space Telescope reveals "The Cat's Eye Nebula" to be one of the most complex planetary nebulae known. ...