Astronomy Picture of the Day

Explanation: How do planets, stars, and galaxies form? How do they evolve? The International Ultraviolet Explorer (IUE) satellite was launched in 1978 and operated by NASA/ ESA/ PPARC to help provide answers to some of the most fundamental questions about the contents of our universe. IUE served as a geostationary orbiting observatory for the next 18 years acquiring over 100,000 observations with its onboard ultraviolet spectrographs. Its prodigious scientific output is only hinted at by the all-sky plot above which shows the locations of IUE's many pointed observations over its long operational history. The brightness of a point on the sky represents the the number of IUE observations. The plot is in galactic coordinates (the plane of our Galaxy runs horizontally through the middle) and reveals the positions of distant quasars, galaxies, stars, star clusters, nebulae, novae, and supernovae - testifying to IUE's broad range of capabilities. The ecliptic plane is also visible running diagonally through the centre, traced out by many observations of solar system objects. After over 18 years, IUE's science operations officially end today as the final commands are transmitted to the aging satellite by controllers at NASA's Goddard Space Flight Centre. Astronomers from around the world whose careers have been touched by IUE have expressed their fond farewells to this most productive and longest lived astronomical satellite and their thanks to all who have made IUE's remarkable voyage of exploration possible.