In 18 eventful years, the Hubble Space Telescope has lived up to its namesake, one of the greatest astronomers in history. Considering its famous rocky birth, breathtaking postcards home, and world-renowned discoveries, it would be hard to argue that a single other scientific instrument has had more widespread impact than Hubble. Frank Summers, an astronomer and outreach scientist at the Space Telescope Science Institute in Baltimore, puts it this way: "I often say to audiences, how many of you can name a particle accelerator? Or a scanning electron microscope? Those are other instruments that have made discoveries on par with Hubble. But they haven't made it into the public vernacular." Maybe it was the mirror flaw, or its triumphant repair; maybe it was the images of the Pillars of Creation, or the Deep Field. Hubble has captured the public's imagination like no other scientific instrument, and has provided unparalleled scientific revelations; it's the source of more than 6,000 research papers. A sampling of Hubble discoveries in the past 18 years: determining the age of the universe; verifying that dark energy is speeding up the universe's expansion; taking photographs of planets outside our solar system, and the chemicals in their atmospheres. Hubble Servicing Mission 4, part of the space shuttle's STS-125 mission, is scheduled for next month. It will be the last time humans visit the orbital observatory; if STS-125 is successful, astronomers hope Hubble will last another 10 years. But they know the telescope's legacy will live far longer. "We've done a lot of looking back over 400 years," Summers said. "Hubble is a fitting successor to the Galileo telescope, because it helped us see things that we've never seen before ... Hubble did play a huge role in transforming people's visions of the universe."

NASA via Hubblesite.org