An anonymous reader quotes a report from Space.com: After more than 20 years of construction, the James Webb Space Telescope (JWST) is complete and, following in-depth testing, the largest-ever space telescope is expected to launch within two years, NASA officials announced today (Nov. 2). NASA Administrator Charles Bolden hosted a news conference to announce the milestone this morning at the agency's Goddard Space Flight Center in Maryland, overlooking the 18 large mirrors that will collect infrared light, sheltered behind a tennis-court-size sun shield. JWST is considered the successor to NASA's iconic Hubble Space Telescope. The telescope will be much more powerful than even Hubble for two main reasons, Mather said at the conference. First, it will be the biggest telescope mirror to fly in space. "You can see this beautiful, gold telescope is seven times the collecting area of the Hubble telescope," Mather said. And second, it is designed to collect infrared light, which Hubble is not very sensitive to. Earth's atmosphere glows in the infrared, so such measurements can't be made from the ground. Hubble emits its own heat, which would obscure infrared readings. JWST will run close to absolute zero in temperature and rest at a point in space called the Lagrange Point 2, which is directly behind Earth from the sun's perspective. That way, Earth can shield the telescope from the sun's infrared emission, and the sun shield can protect the telescope from both bodies' heat. The telescope's infrared view will pierce through obscuring cosmic dust to reveal the universe's first galaxies and spy on newly forming planetary systems. It also will be sensitive enough to analyze the atmospheres of exoplanets that pass in front of their stars, perhaps to search for signs of life, Mather said. The telescope would be able to see a bumblebee a moon's distance away, he added -- both in reflected light and in the body heat the bee emitted. Its mirrors are so smooth that if you stretched the array to the size of the U.S., the hills and valleys of irregularity would be only a few inches high, Mather said.