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.
EUROPEAN SOUTHERN OBSERVATORY
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.
