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History:

Two years after Isaac Newton built the Newtonian reflector, in the year 1670; Johannes Hevelius created a refracting telescope that was a 150 feet long. After almost a decade in 1781, planet Uranus was discovered by Sir William Herschel via a hand-made reflecting telescope. Not too long after, the “Leviathan of Parsontown” was created in 1845. Lord Rosse’s “six-foot diameter primary motor” discovered the first spiral nebulae; “a galaxy having a spiral structure”. Many years passed by until the largest refracting telescope was ever built. The 40 inch telescope was built in 1897 at the Yerkes Observatory.

In the 1940’s, Lyman Spitzer proposed the idea of having an observatory system in space. This idea became a reality on April 25, 1990 when the Hubble Space Telescope was sent into space. Originally, the telescope was supposed to be launched in 1985 but due to the explosion of the space shuttle Challenger, all flights were stopped.The Hubble Space Telescope has made various important discoveries regarding planets, stars and the universe. Many years after the Hubble Space Telescope, the twin-mirrored Large Binocular Telescope was created in 2005. This telescope delivered images 10 times faster that Hubble Space Telescope.

Future The telescope planned to be launched in the year of 2018 is said to “find the first galaxies that formed in the early Universe, connecting the Big Bang to our own Milky Way Galaxy. This large, infrared- optimized telescope is known as the James Webb Space Telescope.

The telescopes main goal will be to observe objects beyond the reach of the universe. Future plans consist of the telescope being placed on the far side of Earth where it will orbit the sun. The James Webb Telescope’s intended use will be for scientific research purposes. Its aim will be to search for stars that were formed after the Big Bang, to study the evolution of galaxies and understand how the planet and the first stars formed.

Impact:

The invention of the telescope had considerable impact on human development and society. The telescope has played an integral role in scientific advancements. The use of the telescope led to the discovery of the planets, as well as playing a pivotal role in determining the shape of the earth, among other things The telescope has allowed human beings to look beyond the earth and provide a clearer picture of the universe. Without the telescope, our understanding and appreciation of the solar system would be much different.

Das, S. (n.d.). 10 Telescopes That Changed Our View of the Universe [Slide Show]:

Scientific American.Science News, Articles and Information | Scientific

American. Retrieved August 7, 2012, from

http://www.scientificamerican.com/article.cfm?id=ten-telescopes-galileo

Types of telescopes

The name "telescope" covers a wide range of instruments. Most detect electromagnetic radiation, but there are major differences in how astronomers must go about collecting light (electromagnetic radiation) in different frequency bands.

Telescopes may be classified by the wavelengths of light they detect:

• X-ray telescopes, using shorter wavelengths than ultraviolet light
• Ultraviolet telescopes, using shorter wavelengths than visible light
• Optical telescopes, using visible light
• Infrared telescopes, using longer wavelengths than visible light
• Submillimetre telescopes, using longer wavelengths than infrared light

Light Comparison
Name	Wavelength	Frequency (Hz)	Photon Energy (eV)
Gamma ray	less than 0.01 nm	more than 10 EHZ	100 keV - 300+ GeV	X
X-Ray	0.01 to 10 nm	30 PHz - 30 EHZ	120 eV to 120 keV	X
Ultraviolet	10 nm - 400 nm	30 EHZ - 790 THz	3 eV to 124 eV
Visible	390 nm - 750 nm	790 THz - 405 THz	1.7 eV - 3.3 eV	X
Infrared	750 nm - 1 mm	405 THz - 300 GHz	1.24 meV - 1.7 eV	X
Microwave	1 mm - 1 meter	300 GHz - 300 MHz	1.24 meV - 1.24 µeV
Radio	1 mm - km	300 GHz - 3 Hz	1.24 meV - 12.4 feV	X

As wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation (although it is possible to make very tiny antenna). The near-infrared can be handled much like visible light, however in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope. For example the James Clerk Maxwell Telescope observes from wavelengths from 3 μm (0.003 mm) to 2000 μm (2 mm), but uses a parabolic aluminum antenna. On the other hand, the Spitzer Space Telescope, observing from about 3 μm (0.003 mm) to 180 μm (0.18 mm) uses a mirror (reflecting optics). Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe from about 0.2 μm (0.0002 mm) to 1.7 μm (0.0017 mm) (from ultra-violet to infrared light).

• Fresnel Imager, an optical lens technology
• X-ray optics, optics for certain x-ray wavelengths

Another threshold in telescope design, as photon energy increases (shorter wavelengths and higher frequency) is the use of fully reflecting optics rather than glancing-incident optics. Telescopes such as TRACE and SOHO use special mirrors to reflect Extreme ultraviolet, producing higher resolution and brighter images than otherwise possible. A larger aperture does not just mean more light is collected, it is collected at a higher diffraction limit.

Telescopes may also be classified by location: ground telescope, space telescope, or flying telescope. They may also be classified by whether they are operated by professional astronomers or amateur astronomers. A vehicle or permanent campus containing one or more telescopes or other instruments is called an observatory.

Optical telescopes

50 cm refracting telescope at Nice Observatory.

Main article: Optical telescope

An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum (although some work in the infrared and ultraviolet). Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness. In order for the image to be observed, photographed, studied, and sent to a computer, telescopes work by employing one or more curved optical elements, usually made from glass lenses and/or mirrors, to gather light and other electromagnetic radiation to bring that light or radiation to a focal point. Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits), spotting scopes, monoculars, binoculars, camera lenses, and spyglasses. There are three main optical types:

• The refracting telescope which uses lenses to form an image.
• The reflecting telescope which uses an arrangement of mirrors to form an image.
• The catadioptric telescope which uses mirrors combined with lenses to form an image.

Beyond these basic optical types there are many sub-types of varying optical design classified by the task they perform such as Astrographs, Comet seekers, Solar telescope, etc.

Radio telescopes

The Very Large Array at Socorro, New Mexico, United States.

Main article: Radio telescope

Radio telescopes are directional radio antennas used for radio astronomy. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed. Multi-element Radio telescopes are constructed from pairs or larger groups of these dishes to synthesize large 'virtual' apertures that are similar in size to the separation between the telescopes; this process is known as aperture synthesis. As of 2005, the current record array size is many times the width of the Earth—utilizing space-based Very Long Baseline Interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite. Aperture synthesis is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and aperture masking interferometry at single reflecting telescopes. Radio telescopes are also used to collect microwave radiation, which is used to collect radiation when any visible light is obstructed or faint, such as from quasars. Some radio telescopes are used by programs such as SETI and the Arecibo Observatory to search for extraterrestrial life.

X-ray telescopes

Einstein Observatory was a space-based focusing optical X-ray telescope from 1978.

Main article: X-ray telescope

X-ray telescopes can use X-ray optics, such as a Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to reflect the rays just a few degrees. The mirrors are usually a section of a rotated parabola and a hyperbola, or ellipse. In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror. Examples of an observatory using this type of telescope are the Einstein Observatory, ROSAT, and the Chandra X-Ray Observatory. By 2010, Wolter focusing X-ray telescopes are possible up to 79 keV.

Gamma-ray telescopes

Higher energy X-ray and Gamma-ray telescopes refrain from focusing completely and use coded aperture masks: the patterns of the shadow the mask creates can be reconstructed to form an image.

X-ray and Gamma-ray telescopes are usually on Earth-orbiting satellites or high-flying balloons since the Earth's atmosphere is opaque to this part of the electromagnetic spectrum. However, high energy x-rays and gamma-rays do not form an image in the same way as telescopes at visible wavelengths. An example of this type of telescope is the Fermi Gamma-ray Space Telescope.

The detection of very high energy gamma rays, with shorter wavelength and higher frequency than regular gamma rays, requires further specialization. An example of this type of observatory is VERITAS. Very high energy gamma-rays are still photons, like visible light, whereas cosmic-rays includes particles like electrons, protons, and heavier nuclei.

A discovery in 2012 may allow focusing gamma-ray telescopes. At photon energizes greater than 700 keV, the index of refraction starts to increase again.

High-energy particle telescopes

High-energy astronomy requires specialized telescopes to make observations since most of these particles go through most metals and glasses.

In other types of high energy particle telescopes there is no image-forming optical system. Cosmic-ray telescopes usually consist of an array of different detector types spread out over a large area. A Neutrino telescope consists of a large mass of water or ice, surrounded by an array of sensitive light detectors known as photomultiplier tubes. Energetic neutral atom observatories like Interstellar Boundary Explorer detect particles traveling at certain energies.

Other types of telescopes

• Gravitational wave detector, aka gravitational wave telescope
• Neutrino detector, aka neutrino telescope

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