1Modern telescopes are enormous scientific instruments, and they are usually built in very remote places.
2Astronomers prefer to build them on high mountains far away from bright city lights.
3At that height the air is thin, dry, and remarkably clear all year round.
4Less air above the telescope means much sharper and clearer images of the stars.
5Some of the largest mirrors in the world measure eight metres across.
6These giant mirrors collect light that has travelled through space for billions of years.
7Fast computers constantly adjust the shape of the mirrors hundreds of times every second.
8This clever technology removes almost all the blur caused by the moving atmosphere.
9Thanks to these telescopes, we have already discovered thousands of planets around distant stars.
10Each new image helps scientists understand how galaxies are formed and how they change.
11Building such a telescope can take more than a decade of work.