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A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.
Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits), spotting scopes, monoculars, binoculars, camera lenses, and spyglasses. An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum (although some work in the infrared and ultraviolet).
The point of radio telescopes is to sense radio waves from space—gas clouds, galaxies, quasars. By the time those celestial objects’ emissions reach Earth, they’ve dimmed to near-nothingness, so astronomers build these gigantic dishes to pick up the faint signals. But their size makes them particularly sensitive to all radio waves, including those from cell phones, satellites, radar systems, spark plugs, microwaves, Wi-Fi, short circuits, and basically anything else that uses electricity or communicates. Protection against radio-frequency interference, or RFI, is why scientists put their radio telescopes in remote locations: the mountains of West Virginia, the deserts of Chile, the way-outback of Australia.
Telescopes may also be classified by location: ground telescope, space telescope, or flying telescope.
The earth’s atmosphere is an imperfect window on the universe. Electromagnetic waves in the optical part of the spectrum (that is, waves longer than X rays and shorter than radio waves) penetrate to the surface of the earth only in a few narrow spectral bands. The widest of the transmitted bands corresponds roughly to the colors of visible light; waves in the flanking ultraviolet and infrared regions of the optical spectrum are almost totally absorbed by the atmosphere. In addition, atmospheric turbulence blurs the images of celestial objects, even when they are viewed through the most powerful ground-based telescopes.
Because the Space Telescope will be immune to the blurring effects of atmospheric turbulence it will be able to obtain much sharper images of celestial objects than ground-based telescopes can, even at the same wavelengths that are observable from the ground. The maximum spatial resolution attainable with the Space Telescope will be on the order of a tenth of an arc-second, most astronomical images made with ground-based instruments have a resolution not much better than an arc-second. The tenfold improvement in resolution will make possible more detailed observations of extended objects. It is also expected to enable astronomers to see stars some seven times farther from the solar system than is now possible.
Accordingly the advantages of making astronomical observations from outside the atmosphere have long been recognized. In the past few decades considerable experience has been gained in the remote operation of telescopes that have been carried above most or all of the atmosphere by suborbital rockets, high-altitude balloons and artificial earth satellites. Significant findings have come from these efforts, altering theories of the structure and evolution of the universe.
Telescope technology
The most important aspect of any telescope is its aperture, the diameter of its main optical component, which can be either a lens or a mirror. A scope’s aperture determines both its light-gathering ability (how bright the image appears) and its resolving power (how sharp the image appears)
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 microwave wavelengths that are longer than those of infrared light
- Radio telescopes that use even longer wavelengths
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.
Radio telescopes are directional radio antennas that typically employ a large dish to collect radio waves. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed. Unlike an optical telescope, which produces a magnified image of the patch of sky being observed, a traditional radio telescope dish contains a single receiver and records a single time-varying signal characteristic of the observed region; this signal may be sampled at various frequencies. In some newer radio telescope designs, a single dish contains an array of several receivers; this is known as a focal-plane array.
By collecting and correlating signals simultaneously received by several dishes, high-resolution images can be computed. Such multi-dish arrays are known as astronomical interferometers and the technique is called aperture synthesis. The ‘virtual’ apertures of these arrays are similar in size to the distance between the telescopes. As of 2005, the record array size is many times the diameter 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.
European Southern Observatory (ESO) to be completed in 2024
The €1.1 billion E-ELT is being built on Cerro Armazones, a 3,000-meter peak about 20 kilometers from ESO’s Paranal Observatory. The access road and leveling of the summit have already been completed, and work on the dome is expected to start onsite in 2017. With a main mirror 39 meters in diameter, the E-ELT will be the largest optical/near-infrared telescope in the world when its construction is completed atop a mountain in the northern Chilean Andes in 2024. Upon completion, the E-ELT’s light-collecting area will be larger than all existing optical research telescopes combined.
The contract—with the ACe Consortium, comprising Astaldi, Cimolai and EIE Group—includes not only an 85-meter-diameter rotating dome with a total mass of 5,000 metric tons, but also the telescope mounting and tube structure, with a total moving mass of more than 3,000 tons. Both of these structures will be by far the largest ever built for an optical/infrared telescope. The dome will rise to almost 80 meters in height and its footprint will be comparable in area to a soccer pitch.
It’s 128-foot mirror is composed of 798 individual 1.4-meter segments, allowing it to look further into space than any other astronomical tool in existence. The observatory will use advanced optics to compensate for atmospheric distortion and expected to produce images 16 times sharper than the orbiting Hubble Space Telescope. The telescope is designed to tackle a wide variety of challenging astronomical studies, including detailed studies of subjects including planets around other stars, nearby galaxies, supermassive black holes, and the nature and distribution of the dark matter and dark energy which dominate the universe.
The first six hexagonal segments for the main mirror of ESO’s Extremely Large Telescope (ELT) have been successfully cast by the German company SCHOTT at their facility in Mainz in 2018. These segments will form parts of the ELT’s 39-metre main mirror, which will have 798 segments in total when completed. Marc Cayrel, head of ELT optomechanics at ESO, was present at the first castings: “It was a wonderful feeling to see the first segments being successfully cast. This is a major milestone for the ELT!”
As with the telescope’s secondary mirror blank, the ELT main mirror segments are made from the low-expansion ceramic material Zerodur© from SCHOTT. ESO has awarded this German company with contracts to manufacture the blanks of the first four ELT mirrors (known as M1 to M4, with M1 being the primary mirror) (eso1704). The first segment castings are important as they allow the engineers at SCHOTT to validate and optimise the manufacturing process and the associated tools and procedures.
The casting of the first six segments is a major milestone, but the road ahead is long — in total more than 900 segments will need to be cast and polished (798 for the main mirror itself, plus a spare set of 133). When fully up to speed, the production rate will be about one segment per day. After casting, the mirror segment blanks will go through a slow cooling and heat treatment sequence and will then be ground to the right shape and polished to a precision of 15 nanometres across the entire optical surface. The shaping and polishing will be performed by the French company Safran Reosc, which will also be responsible for additional testing (eso1717).
Among the E-ELT’s primary instruments will be:
· HARMONI (High Angular Resolution Monolithic Optical and Near-infrared Integral) field spectrograph—which will function as the telescope’s workhorse instrument for spectroscopy in the wavelength range 0.47–2.45 µm. HARMONI will be optimized to exploit the best image quality delivered from a post-focal laser tomographic adaptive optics module.
· MAORY (Multi-conjugate Adaptive Optics Relay)—an adaptive optics module designed to help compensate for distortions caused by turbulence in the Earth’s atmosphere. MAORY is designed to work with the imaging camera MICADO to provide stable and sharp images across a large field of view in the near-infrared (wavelengths from 0.8–2.4µm) to allow scientists to make precise measurements of the positions, brightness and motions of stars.
· METIS (Mid-infrared E-ELT Imager and Spectrograph)—which will use the 39-meter main mirror of the telescope to focus on exoplanets, proto-planetary disks, Solar System bodies, active galactic nuclei and high-redshift infrared galaxies.
Astronomers expect at least two of the E-ELT instruments will include a coronagraph that will be used to block out a star’s light in order to directly image and characterize earthlike extrasolar planets in habitable zones around their parent stars. This should enable measure of their physical properties, including their atmospheres.
“The E-ELT will produce discoveries that we simply cannot imagine today, and it will inspire people around the world to think about science, technology and our place in the universe,” says Tim de Zeeuw, ESO’s director general.
James Webb Space Telescope
The James Webb Space Telescope (JWST) is a space telescope designed primarily to conduct infrared astronomy. As the largest optical telescope in space, its greatly improved infrared resolution and sensitivity allow it to view objects too early, distant, or faint for the Hubble Space Telescope. This is expected to enable a broad range of investigations across the fields of astronomy and cosmology, such as observation of the first stars and the formation of the first galaxies, and detailed atmospheric characterization of potentially habitable exoplanets.
The U.S. National Aeronautics and Space Administration (NASA) led JWST’s development in collaboration with the European Space Agency (ESA) and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center (GSFC) in Maryland managed telescope development, the Space Telescope Science Institute in Baltimore on the Homewood Campus of Johns Hopkins University operates JWST, and the prime contractor was Northrop Grumman.
JWST’s primary mirror consists of 18 hexagonal mirror segments made of gold-plated beryllium, which combined create a 6.5-meter-diameter (21 ft) mirror, compared with Hubble’s 2.4 m (7 ft 10 in). This gives JWST a light-collecting area of about 25 square meters, about six times that of Hubble. Unlike Hubble, which observes in the near ultraviolet and visible (0.1 to 0.8 μm), and near infrared (0.8–2.5 μm) spectra, JWST observes in a lower frequency range, from long-wavelength visible light (red) through mid-infrared (0.6–28.3 μm).
The telescope must be kept extremely cold, below 50 K (−223 °C; −370 °F), such that the infrared light emitted by the telescope itself does not interfere with the collected light. It is deployed in a solar orbit near the Sun–Earth L2 Lagrange point— a gravitationally stable location in space, about 1.5 million kilometers (930,000 mi) from Earth, where its five-layer sunshield protects it from warming by the Sun, Earth, and Moon. The James Webb Space Telescope was launched on 25 December 2021 on an Ariane 5 rocket from Kourou, French Guiana, and arrived at the Sun–Earth L2 Lagrange point in January 2022. L2 is a spot in space near Earth that lies opposite from the sun; this orbit will allow the telescope to stay in line with Earth as it orbits the sun
The $10 billion James Webb Space Telescope — NASA’s largest and most powerful space science telescope — will probe the cosmos to uncover the history of the universe from the Big Bang to alien planet formation and beyond. It is one of NASA’s Great Observatories, huge space instruments that include the likes of the Hubble Space Telescope to peer deep into the cosmos.
In July 2022, NASA announced that all 17 of the observatory scientific instrument ‘modes’ have been fully vetted and that the James Webb Space Telescope is ready to begin its epic science mission. Thanks to a successful and precise launch, NASA announced that the JWST should have enough fuel to more than double its minimum mission life expectancy of 10 years.
NSF grant accelerates development for one of the world’s most powerful telescopes in Sep 2020
The Giant Magellan Telescope, of which the University of Chicago is a founding member, has received a $17.5 million grant from the National Science Foundation to accelerate the prototyping and testing of some of the most powerful optical and infrared technologies ever engineered.
These crucial advancements for the Giant Magellan Telescope at the Las Campanas Observatory in Chile will allow astronomers to see farther into space with more detail than any other optical telescope before. The NSF grant positions the telescope to be one of the first in a new generation of large telescopes, approximately three times the size of any ground-based optical telescope built to date.
The GMT and the Thirty Meter Telescope are a part of the U.S. Extremely Large Telescope Program (US-ELTP), a joint initiative with NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab) to provide observing access to the entire sky as never before. Upon completion of each telescope, U.S. scientists and international partners will be able to take advantage of the program’s two pioneering telescopes to carry out transformational research that answers some of humanity’s most pressing questions, such as whether we are alone in the universe and where we come from. “We are honored to receive our first NSF grant,” said Robert Shelton, president of the GMTO Corporation. “It is a giant step toward realizing the GMT’s scientific goals and the profound impact the GMT will have on the future of human knowledge.”
“This telescope will boost virtually every area of astronomy and in many cases, make transformative discoveries,” said Michael Gladders, professor of astronomy and astrophysics at UChicago and member of the GMT’s science committee. “More broadly, the involvement of NSF is a wonderful and important step for the entire astronomical community, as we look to bring access to more astronomers at every U.S. institution.”
Chinese Five-hundred-meter Aperture Spherical Telescope declared fully operational on 11 January 2020
Sky Eye, which is offically known as the Five-hundred-meter Aperture Spherical Telescope (FAST), is the the largest and most sensitive single-dish radio telescope in the world. A engineering marvel, its gargantuan structure is built inside a natural basin in the mountains of Guizhou, China.
The Five-hundred-meter Aperture Spherical radio Telescope (FAST; Chinese: 五百米口径球面射电望远镜), nicknamed Tianyan (天眼, lit. “Sky’s/Heaven’s Eye”), is a radio telescope located in the Dawodang depression (大窝凼洼地), a natural basin in Pingtang County, Guizhou, southwest China. FAST has a 500 m (1,600 ft) diameter dish constructed in a natural depression in the landscape. It is the world’s largest filled-aperture radio telescope and the second-largest single-dish aperture, after the sparsely-filled RATAN-600 in Russia.
The telescope is so huge it can’t be physically tilted, but it can be pointed in a direction by thousands of actuators that deform the telescope’s reflective surface. By deforming the surface, the location of the telescope’s focal point changes, and the telescope can look at a different part of the sky.
The world’s second-largest radio telescope, at the Arecibo Observatory in Puerto Rico, was destroyed when its suspended 900-tonne receiver platform came loose and plunged 140 metres (450 feet) onto the radio dish below. The Chinese installation in Pingtang, Guizhou province, is up to three times more sensitive than the US-owned one, and is surrounded by a five-kilometre (three-mile) “radio silence” zone where mobile phones and computers are not allowed.
It has a novel design, using an active surface made of 4,500 panels to form a moving parabola metal panels in real time. The cabin containing the feed antenna, suspended on cables above the dish, can move automatically by using winches to steer the instrument to receive signals from different directions. It observes at wavelengths of 10 cm to 4.3 m. Construction of FAST began in 2011. It observed first light in September 2016. After three years of testing and commissioning, it was declared fully operational on 11 January 2020.
FAST sifts through enormous amounts of data. The telescope feeds 38 billion samples a second into a cluster of high-performance computers, which then produces exquisitely detailed charts of incoming radio signals. These charts are then searched for signals that look like technosignatures.
With such a large collecting area, FAST can pick up incredibly faint signals. It is about 20 times more sensitive than Australia’s Murriyang telescope at the Parkes Radio Observatory. FAST could easily detect a transmitter on a nearby exoplanet with a similar output power to radar systems we have here on Earth.
FAST detects radiation at radio wavelengths (up to 10 cm) and is used for astronomical research in a wide range of areas. One area is the search for extraterrestrial intelligence or SETI. SETI observations are mainly done in “piggy-back” mode, which means they are taken while the telescope is also running its primary science programs.
The telescope made its first discovery, of two new pulsars, in August 2017. The new pulsars PSR J1859-01 and PSR J1931-02—also referred to as FAST pulsar #1 and #2 (FP1 and FP2), were detected on 22 and 25 August 2017; they are 16,000 and 4,100 light years away, respectively. Parkes Observatory in Australia independently confirmed the discoveries on 10 September 2017. By September 2018, FAST had discovered 44 new pulsars.
Military requirements
The US Strategic Command defines SSA as “The requisite current and predictive knowledge of space events, threats, activities, conditions and space system (space, ground, link) status capabilities, constraints and employment — to current and future, friendly and hostile– to enable commanders, decision makers, planners and operators to gain and maintain space superiority across the spectrum of conflict.”
SSA encompasses surveillance of all space objects, activities, and terrestrial support systems (satellites & debris), more detailed reconnaissance of specific space objects assets (mission identification, capabilities, vulnerabilities, etc.), discerning the intent of others who operate in space, knowing the status of our own forces in real-time, and analysis of the space environment and its effects (solar storms, meteor showers, etc.).
Comprehensive SSA requires a networked system of radars and electro-optical sensors. Low altitude debris is usually observed by radar ground stations while high altitude debris is observed by optical ground stations. Bistatic, multistatic and phased array radars are widely used. The optical telescopes have some disadvantages like they can only track objects that are illuminated while the telescopes are in darkness. Almost without exception, objects are extremely difficult to monitor as they pass between the earth and the sun. Daylight observations, in general, pose a significant challenge for groundbased optical sensors. Space-based sensors can provide observations much closer to the sun, but all space-based sensors are still limited when the target is positioned between the sensor and the sun.
When considering only ground-based optical telescopes, the trade space ranges from large networks of small telescopes to small networks (or single copies) of large telescopes. The Russian International Scientific Optical Network (ISON) network represents an excellent example of a large network of what are mostly smaller telescopes. ISON has a very interesting mix of telescopes and optical designs, but most of their assets are in the 50 cm and smaller aperture class. What makes ISON interesting is that they have observation locations distributed
around the globe. One obvious weakness in their network is the limited coverage over the central to eastern Pacific Ocean.
Given that the ISON telescopes are generally smaller in aperture, they are limited to observing GEO satellites in the 15th to 16th magnitude range. Small telescopes are extremely inexpensive and can easily be deployed to remote locations, provided power and communications are available. Small telescopes often have very wide fields of view allowing them to rapidly scan the entire visible
GEO belt several times each night.
The GEODSS network represents an example of a small number of medium aperture telescopes. With an aperture of 1 m the telescopes are more sensitive than most in ISON, but with only three operational locations, GEODSS leaves parts of the GEO belt without coverage.
A U.S.-developed space surveillance telescope has been assembled at a new facility in Western Australia and is expected to start operating in 2022, the U.S. Space Force Space and Missile Systems Center announced April 2020. . Between 2011 and 2017 the telescope was tested at the Atom Site on White Sands Missile Range in New Mexico. DARPA handed over the telescope to the U.S. Air Force in 2017.
The SST is an example of a small network composed of large-aperture telescopes. In the case of SST, there is only one. The telescope is capable of scanning the entire sky several times each night and recording GEO objects to magnitudes as faint as 19.5. The system cost, however, is extremely high, almost to the point of being too expensive.
AFRL operates two major telescope sites that are used to advance Space Situational Awareness (SSA) technologies. The Starfire Optical Range (SOR) is located on Kirtland Air Force Base, New Mexico, and the Air Force Maui Optical and Super Computing (AMOS) site is located in Maui, Hawaii. The AMOS site houses the military’s largest ground-based electro-optical telescope, the Advanced Electro-Optical System 3.6-meter telescope. The laser from the AEOS creates an artificial guide star 60 miles above the surface of the earth that when used with adaptive optics on the telescope reduces the blurring effects of atmospheric turbulence, providing a clearer view of objects in space. The SOR operates one of the world’s premier adaptive-optics telescopes capable of tracking low-earth orbiting satellites. Using adaptive optics, this 3.5-meter telescope distinguishes basketball-sized objects at a distance of 1,000 miles into space.
Recently the trend is to use space based sensors to provide timely detection, collection, identification and tracking of man-made space objects from deep space to LEO orbits. When building space-based SSA assets, the first choice is between deploying them in LEO or
some higher orbit, close to, but not specifically in GEO. Basing in LEO is less expensive and the radiation environment is more benign, but one must also contend with substantial earth blockage.
Recent events such as moon race and asteroid mining have made the cislunar space, the entire space extending beyond Earth to the moon next “high ground” a position of advantage or superiority that needs to be monitored and controlled. The cis-lunar domain is defined as that area of deep space under the gravitational influence of the earth-moon system. This includes a set of earth-centered orbital locations in low earth orbit (LEO), geosynchronous earth orbit (GEO), highly elliptical and high earth orbits (HEO), earth-moon libration or “Lagrange” points (E-ML1 through E-ML5, and in particular, E-ML1 and E-ML2), and low lunar orbit (LLO). Now with space competition and future militarization has reached to Cislunar Space, militaries are extending the Space situational awareness (SSA) to this entire space betweeen earth and moon.
