TELESCOPES
Telescopes can be divided into two broad categories - optical and non-optical telescopes. Optical telescopes are used to view visible light and we usually view the image directly with our eyes. However, The Hubble Space Telescope and the VLT (Very Large Telescope) take digital pictures of the images and store them.
Non-optical telescopes view other types of light on the electromagnetic spectrum.
Radio telescopes are large dish antennas used singularly or in an array. Because radio wavelengths are much longer than visible light, radio telescopes must be very large to achieve images which are similar resolution to optical telescopes.
Infrared telescopes detect infrared radiation from warm objects so they need to be shielded from local heat sources. They can be chilled with liquid nitrogen or situated in polar regions. They are used to view radiation sources outside the Earth's atmosphere such as nebulae, young stars, and gas and dust in other galaxies.
Ultraviolet telescopes measure ultraviolet radiation. The ozone layer surrounding the earth blocks most ultraviolet radiation so these types of telescopes must be launched by rockets or positioned on satellites to make observations from above the Earths atmosphere. Some of the hottest stars in the universe are studied with Ultraviolet telescopes.
Xray telescopes are useful for detecting very hot gases such as the space between galaxies in galaxy clusters. Xrays are also affected by the Earths atmosphere so xray telescopes need to be positioned in space.
Gamma-rays are the shortest rays in the electromagnetic spectrum and gamma-ray telescopes are used to view high energy objects such as supernovas and neutron stars. They are fixed to spacecraft to deliver information from well outside the Earth's atmosphere.