In 1609, Galileo became the first astronomer to use a telescope to observe the night sky. His optical telescope picked up light waves from previously indistinct stars and planets. Since then, scientists have developed telescopes to detect other objects in space, such as pulsars, quasars, neutron stars and black holes, which emit different types and intensities of wavelength. Ground-based instruments can measure some of these, but others are observed more effectively from space.
Types of ground-based telescopes
Astronomers mainly use optical or radio telescopes terrestrially. Optical telescopes collect and focus light waves from stars, planets and galaxies, using either refraction from a concave glass surface or reflection from mirrors. Radio telescopes measure the long-wavelength radio waves produced at specific frequencies by all objects in space. These can include things invisible to optical telescopes, such as the cold clouds of hydrogen associated with the inception of stars, and the hot gases surrounding black holes. To sharpen the resolution, computers combine the signals from an array of two or more radio telescopes through the process of interferometry. Certain ground-based telescopes, such as those at Mauna Kea in Hawaii, can also detect infra-red activity from red giants (huge burning-out stars).
Ground-based telescopes are less expensive to build and operate than instruments on satellites or space stations. They can be continually maintained and updated by engineers on the ground without the dangers and complications of sending astronauts into space. The range of research available through ground-based sites is continually developing through international collaboration -- for example, to co-ordinate the results from arrays of radio telescopes in different countries -- and through advanced technology allowing high-resolution imagery from optical telescopes.
Cloudy weather, air pollution and light spill from towns and cities limit the capabilities of ground-based optical telescopes. Radio telescopes extend the range of astronomical research using low-frequency wavelengths; they can operate by day or night and are unaffected by atmospheric pollution or dust particles in space. However, scientists need space telescopes to detect other types of electro-magnetic radiation, which are blocked by the Earth’s atmosphere; for example, ultra-violet radiation from quasars, X-rays from neutron stars and gamma rays from black holes.
The most favourable locations for ground-based observatories are those with clear skies, calm weather and an atmosphere free from dust, moisture and light pollution; in other words, at a distance from deserts, mountain ranges and cities. Combining data from telescopes in the northern and southern hemispheres enables the rapid development of astrophysics worldwide.