Optical observatories study the visible radiation (light) from objects in space, and most are located high up on mountaintops where the air is thinner, drier, and less polluted than at lower altitudes. But there are also observatories with telescopes that can detect invisible forms of radiation, such as gamma rays, infrared rays, and radio waves. Observatories in space are also used to detect these rays, as well as X-rays and ultraviolet rays.
The most powerful telescope on Earth is the Very Large Telescope (VLT) of the European Southern Observatory in Chile. The VLT is made up of four telescopes working together. Each has a mirror 8.2 m (27 ft) across – a billion times more powerful than the naked eye. The VLT is returning some of the best images of the Universe seen so far.
Mauna Kea Observatory in Hawaii sits on the summit of an extinct volcano. Inside the open dome is one of the giant Keck telescopes. There are two Keck telescopes, each with a mirror 10 m (33 ft) across. A single mirror of this size would bend under its own weight. Instead, the mirrors are made up of 36 hexagonal (six-sided) sections which can be adjusted to get the best views of space.
In New Mexico, USA, there is a group of 27 radio telescopes called the Very Large Array. The telescopes work together, acting as one big dish around 27 km (17 miles) across. Radio signals are collected by the dish and reflected onto a central antenna. The signals are then fed to a receiver and are processed to produce pictures, called radio images.