Optical telescopes

At the top of Mount Hamilton, near San Jose, California, Lick Observatory looks out over the dense sprawl of the San Francisco Bay Area. On a clear day from the 4,200-foot summit, you can see San Francisco to the north, as well as the entrance to Yosemite Valley, 120 miles east, as the crow flies. At night you can see even farther — millions of light-years into space.

Scientists and engineers from three space agencies worked for 20 years to complete the $10bn telescope

Though assessments are still continuing, the telescope still appears to be operating well enough

In 1610, Galileo used a telescope to discover the four largest moons of Jupiter, and for more than two hundred years the only way to get a better look at the night sky was to build a bigger telescope. In the 19th century, astronomers began hauling telescopes up mountains to reduce the amount of atmospheric interference blurring their observations.