Before 1990, our view of space came from ground-based light telescopes. The images were interesting, but not very clear, and the optics couldn't see far enough to give us the views astronomers had in mind. Earth's atmosphere, with all its clouds, water and gas vapors, isn't terribly conducive to conducting light, a requirement for capturing clear images.
The solution was clear: Put a telescope on the other side of Earth's atmosphere, where the light would travel to distant objects and bounce back unhindered. Named after astronomer Edwin Hubble, the telescope offered the first clear views of the universe beyond our galaxy. Hubble developed a theory based on the changing nature of stars light years away. The Hubble Space Telescope would let astronomers prove his theory that the universe is expanding.
The work began in 1975. It took 15 years to launch Hubble. Scientists spent eight years assembling and testing the telescope's 400,000 parts and 26,000 miles (41,843 km) of wiring. It would have been in orbit in the late '80s, but the Challenger disaster in 1986 pushed the launch date back to 1990.
The Hubble Space Telescope lets us watch the expansion of the universe in a way never before imagined. Not only does it have 10 times the resolution of a ground-based telescope and 50 times the sensitivity, but another development around the same time made its unprecedented views of the universe more accessible than any previous scientific advance. With the advent of the Internet, people could sit at home and watch the universe unfold in all hi-resolution, full-color glory. Hubble revealed the world, going out billions of light years from Earth, to anyone who cared to see it.
Of course, Hubble was only state-of-the-art for a short time. As is typical with scientific innovations, it was outdated in less than a decade. The Chandra telescope uses X-rays instead of visible light to capture the most amazing views of the universe to date.