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128-534: The basic elements of the telescope are the optics (focusing or collimating ), that collects the radiation entering the telescope, and the detector , on which the radiation is collected and measured. A variety of different designs and technologies have been used for these elements. Many X-ray telescopes on satellites are compounded of multiple small detector-telescope systems whose capabilities add up or complement each other, and additional fixed or removable elements (filters, spectrometers) that add functionalities to

256-795: A Delta IV from Cape Canaveral LC37B on May 24, 2006. However, there have been no GOES 13 SXI images since December 2006. The Russian-German Spektr-RG carries the eROSITA telescope array as well as the ART-XC telescope. It was launched by Roscosmos on 13 July 2019 from Baikonur and began collecting data in October 2019. The most common methods used in X-ray optics are grazing incidence mirrors and collimated apertures . Only three geometries that use grazing incidence reflection of X-rays to produce X-ray images are known: Wolter system , Kirkpatrick-Baez system , and lobster-eye optics . A simple parabolic mirror

384-554: A Delta IV M+ (4,2) . It underwent Post-Launch Testing until December 2009 and then was placed in on-orbit storage. This satellite is a part of the GOES-N Series. GOES-14 has been and will be activated should another GOES satellite suffer a problem or be decommissioned. It was temporarily designated GOES-East because of technical difficulties with GOES-13 and moved towards the GOES-East location. After resolution of those problems, GOES-14

512-422: A graveyard orbit . It no longer had the fuel for required maneuvers to keep it on station. GOES-11 , which was designated GOES-L before orbiting, had a partial failure on 6 December 2011. It was decommissioned on 16 December 2011 and boosted into a graveyard orbit. GOES-12 , which was designated GOES-M before orbiting, was decommissioned on 16 August 2013 and boosted into a graveyard orbit. GOES-13 , which

640-421: A phoswich of sodium iodide and caesium iodide. In electronics , modulation is the process of varying one waveform in relation to another waveform. With a 'modulation collimator' the amplitude (intensity) of the incoming X-rays is reduced by the presence of two or more 'diffraction gratings' of parallel wires that block or greatly reduce that portion of the signal incident upon the wires. An X-ray collimator

768-459: A GOES satellite is launched successfully, it is redesignated with a number (1, 2, 3, etc.). So, GOES-A to GOES-F became GOES-1 to GOES-6. Because GOES-G was a launch failure, it never received a number. GOES-H to GOES-R became GOES-7 to GOES-16 (skipping GOES-Q, which was not built). Once operational, the different locations used by the satellites are given a name corresponding to the regions they cover. These are GOES-East and GOES-West, which watch

896-481: A bismuth germinate (BGO) crystal 78 mm in diameter by 120 mm thick. The KONUS-B instrument consisted of seven detectors distributed around the spacecraft that responded to photons of 10 keV to 8 MeV energy. They consisted of NaI (Tl) scintillator crystals 200 mm in diameter by 50 mm thick behind a Be entrance window. Kvant-1 carried the HEXE, or High Energy X-ray Experiment, which employed

1024-430: A broad band, or extremely low reflectivity at a single wavelength. Constructive interference in thin films can create a strong reflection of light in a range of wavelengths, which can be narrow or broad depending on the design of the coating. These films are used to make dielectric mirrors , interference filters , heat reflectors , and filters for colour separation in colour television cameras. This interference effect

1152-619: A changing index of refraction; this principle allows for lenses and the focusing of light. The simplest case of refraction occurs when there is an interface between a uniform medium with index of refraction n 1 and another medium with index of refraction n 2 . In such situations, Snell's Law describes the resulting deflection of the light ray: n 1 sin ⁡ θ 1 = n 2 sin ⁡ θ 2 {\displaystyle n_{1}\sin \theta _{1}=n_{2}\sin \theta _{2}} where θ 1 and θ 2 are

1280-399: A converging lens has positive focal length, while a diverging lens has negative focal length. Smaller focal length indicates that the lens has a stronger converging or diverging effect. The focal length of a simple lens in air is given by the lensmaker's equation . Ray tracing can be used to show how images are formed by a lens. For a thin lens in air, the location of the image is given by

1408-443: A critical part of communications between the U.S. and Amundsen–Scott South Pole Station before being decommissioned in 2016. Geostationary satellites expend fuel to keep themselves stationary over the equator, and thus cannot normally ordinarily be seen from the poles. When that fuel is depleted, solar and lunar perturbations increase the satellite's inclination so that its ground track begins to describe an analemma (a figure-8 in

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1536-443: A flat aperture patterned grille in front of the detector. This design gives results that are less sensitive than focusing optics; also the imaging quality and identification of source position is much poorer. Though this design offers a larger field of view and can be employed at higher energies, where grazing incidence optics become ineffective. Also the imaging is not direct, but the image is rather reconstructed by post-processing of

1664-715: A gap in the sensor capabilities of GOES-17 due to a hardware issue. Like GOES-13, GOES-15 was then transferred to the U.S. Space Force and renamed EWS-G2 to monitor the Indian Ocean until approximately 2030. Designed to operate in geostationary orbit 35,790 kilometres (22,240 mi) above the Earth, the GOES spacecraft continuously view the continental United States , the Pacific and Atlantic Oceans, Central America , South America , and southern Canada. The three-axis, body-stabilized design enables

1792-700: A platform for the Solar X-Ray Imager (SXI) and space environment monitoring (SEM) instruments. The SXI provides high-cadence monitoring of large scale solar structures to support the Space Environment Services Center's (SESC) mission. The SXI unit on GOES-13, however, was damaged by a solar flare in 2006. The SESC, as the nation's "space weather" service, receives, monitors, and interprets a wide variety of solar-terrestrial data. It also issues reports, alerts, and forecasts for special events such as solar flares or geomagnetic storms. This information

1920-477: A single scalar quantity to represent the electric field of the light wave, rather than using a vector model with orthogonal electric and magnetic vectors. The Huygens–Fresnel equation is one such model. This was derived empirically by Fresnel in 1815, based on Huygens' hypothesis that each point on a wavefront generates a secondary spherical wavefront, which Fresnel combined with the principle of superposition of waves. The Kirchhoff diffraction equation , which

2048-422: A single photon can produce a single electron of charge in a pixel, and an image is built up by accumulating many such charges from many photons during the exposure time. When an X-ray photon hits a CCD, it produces enough charge (hundreds to thousands of electrons, proportional to its energy) that the individual X-rays have their energies measured on read-out. Microcalorimeters can only detect X-rays one photon at

2176-522: A single point on the image, while chromatic aberration occurs because the index of refraction of the lens varies with the wavelength of the light. In physical optics, light is considered to propagate as waves. This model predicts phenomena such as interference and diffraction, which are not explained by geometric optics. The speed of light waves in air is approximately 3.0×10  m/s (exactly 299,792,458 m/s in vacuum ). The wavelength of visible light waves varies between 400 and 700 nm, but

2304-437: A spectrum. The discovery of this phenomenon when passing light through a prism is famously attributed to Isaac Newton. Some media have an index of refraction which varies gradually with position and, therefore, light rays in the medium are curved. This effect is responsible for mirages seen on hot days: a change in index of refraction air with height causes light rays to bend, creating the appearance of specular reflections in

2432-544: A team led by the Weather Systems division of L3Harris , including subcontracts to Boeing, Atmospheric and Environmental Research (AER), Honeywell , Carr Astronautics, Wyle Laboratories , and Ares . GOES spacecraft have been manufactured by Boeing (GOES-D through -H and GOES-N through -P) and Space Systems/Loral (GOES-A through -C and GOES-I through -M). The GOES-I series (I-M) and the GOES-N series (N-P) are documented in

2560-465: A thickness of one-fourth the wavelength of incident light. The reflected wave from the top of the film and the reflected wave from the film/material interface are then exactly 180° out of phase, causing destructive interference. The waves are only exactly out of phase for one wavelength, which would typically be chosen to be near the centre of the visible spectrum, around 550 nm. More complex designs using multiple layers can achieve low reflectivity over

2688-480: A thin layer of a reflective material (typically gold or iridium ). Mirrors based on this construction work on the basis of total reflection of light at grazing incidence. This technology is limited in energy range by the inverse relation between critical angle for total reflection and radiation energy. The limit in the early 2000s with Chandra and XMM-Newton X-ray observatories was about 15 kilo- electronvolt (keV) light. Using new multi-layered coated mirrors,

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2816-456: A time (but can measure the energy of each). Transition-edge sensors are the next step in microcalorimetry. In essence they are super-conducting metals kept as close as possible to their transition temperature. This is the temperature at which these metals become super-conductors and their resistance drops to zero. These transition temperatures are usually just a few degrees above absolute zero (usually less than 10 K ). Optics Optics

2944-476: A variety of technologies and everyday objects, including mirrors , lenses , telescopes , microscopes , lasers , and fibre optics . Optics began with the development of lenses by the ancient Egyptians and Mesopotamians . The earliest known lenses, made from polished crystal , often quartz , date from as early as 2000 BC from Crete (Archaeological Museum of Heraclion, Greece). Lenses from Rhodes date around 700 BC, as do Assyrian lenses such as

3072-525: A wide range of scientific topics, and discussed light from four different perspectives: an epistemology of light, a metaphysics or cosmogony of light, an etiology or physics of light, and a theology of light, basing it on the works of Aristotle and Platonism. Grosseteste's most famous disciple, Roger Bacon , wrote works citing a wide range of recently translated optical and philosophical works, including those of Alhazen, Aristotle, Avicenna , Averroes , Euclid, al-Kindi, Ptolemy, Tideus, and Constantine

3200-587: A year apart, on 16 June 1977 and 1978 respectively. Prior to the GOES satellites two Synchronous Meteorological Satellites (SMS) satellites had been launched; SMS-1 in May 1974, and SMS-2 in February 1975. The SMS-derived satellites were spin-stabilized spacecraft, which provided imagery through a Visible and Infrared Spin Scan Radiometer , or VISSR. The first three GOES satellites used a Philco-Ford bus developed for

3328-522: Is a device that filters a stream of X-rays so that only those traveling parallel to a specified direction are allowed through. Minoru Oda , President of Tokyo University of Information Sciences, invented the modulation collimator, first used to identify the counterpart of Sco X-1 in 1966, which led to the most accurate positions for X-ray sources available, prior to the launch of X-ray imaging telescopes. SAS 3 carried modulation collimators (2-11 keV) and Slat and Tube collimators (1 up to 60keV). On board

3456-448: Is a material which exhibits the property of luminescence when excited by ionizing radiation . Luminescent materials, when struck by an incoming particle, such as an X-ray photon, absorb its energy and scintillate, i.e. reemit the absorbed energy in the form of a small flash of light, typically in the visible range. The scintillation X-ray detector were used on Vela 5A and its twin Vela 5B ;

3584-591: Is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics. Historically, the ray-based model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that light waves were in fact electromagnetic radiation. Some phenomena depend on light having both wave-like and particle-like properties . Explanation of these effects requires quantum mechanics . When considering light's particle-like properties,

3712-427: Is a simple paraxial physical optics model for the propagation of coherent radiation such as laser beams. This technique partially accounts for diffraction, allowing accurate calculations of the rate at which a laser beam expands with distance, and the minimum size to which the beam can be focused. Gaussian beam propagation thus bridges the gap between geometric and physical optics. In the absence of nonlinear effects,

3840-506: Is a type of gaseous ionization detector that counts particles of ionizing radiation and measures their energy. It works on the same principle as the Geiger-Müller counter , but uses a lower operating voltage . All X-ray proportional counters consist of a windowed gas cell. Often this cell is subdivided into a number of low- and high-electric field regions by some arrangement of electrodes. Proportional counters were used on EXOSAT , on

3968-543: Is also what causes the colourful rainbow patterns seen in oil slicks. Geostationary Operational Environmental Satellite The Geostationary Operational Environmental Satellite ( GOES ), operated by the United States' National Oceanic and Atmospheric Administration (NOAA)'s National Environmental Satellite, Data, and Information Service division, supports weather forecasting , severe storm tracking, and meteorology research. Spacecraft and ground-based elements of

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4096-481: Is based on a Fourier-transform technique using a set of 9 Rotational Modulation Collimators . OSO 8 had on board a Graphite Crystal X-ray Spectrometer, with energy range of 2-8 keV, FOV 3°. The Granat ART-S X-ray spectrometer covered the energy range 3 to 100 keV, FOV 2° × 2°. The instrument consisted of four detectors based on spectroscopic MWPCs , making an effective area of 2,400 cm at 10 keV and 800 cm at 100 keV. The time resolution

4224-486: Is considered to travel in straight lines, while in physical optics, light is considered as an electromagnetic wave. Geometrical optics can be viewed as an approximation of physical optics that applies when the wavelength of the light used is much smaller than the size of the optical elements in the system being modelled. Geometrical optics , or ray optics , describes the propagation of light in terms of "rays" which travel in straight lines, and whose paths are governed by

4352-484: Is derived using Maxwell's equations, puts the Huygens-Fresnel equation on a firmer physical foundation. Examples of the application of Huygens–Fresnel principle can be found in the articles on diffraction and Fraunhofer diffraction . More rigorous models, involving the modelling of both electric and magnetic fields of the light wave, are required when dealing with materials whose electric and magnetic properties affect

4480-633: Is disseminated to users. Additionally, anyone may receive data directly from the satellites by utilizing a small dish , and processing the data with special software. The GOES satellites are controlled from the Satellite Operations Control Center in Suitland, Maryland. During significant weather or other events, the normal schedules can be altered to provide the coverage requested by the NWS and other agencies. GOES-12 and above also have provided

4608-476: Is important to the operation of military and civilian radio wave and satellite communication and navigation systems. The information also is important to electric power networks, the missions of geophysical explorers, Space Station astronauts, high-altitude aviators, and scientific researchers. The SEM measures the effect of the Sun on the near-Earth solar-terrestrial electromagnetic environment, providing real-time data to

4736-476: Is operated for more than 25 years in a high elliptical orbit, returning thousands 0.5 arc-second images and high-resolution spectra of all kinds of astronomical objects in the energy range from 0.5 to 8.0 keV. Chandra's resolution is about 50 times superior to that of ROSAT. Satellites in use today include ESA 's XMM-Newton observatory (low to mid energy X-rays 0.1-15 keV), NASA 's Swift observatory, Chandra observatory and IXPE telescope. JAXA has launched

4864-502: Is the branch of physics that studies the behaviour and properties of light , including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible , ultraviolet , and infrared light. Light is a type of electromagnetic radiation , and other forms of electromagnetic radiation such as X-rays , microwaves , and radio waves exhibit similar properties. Most optical phenomena can be accounted for by using

4992-402: Is thick enough that virtually none are able to penetrate from outer space all the way to the Earth's surface. X-rays in the 0.5 to 5 keV (80 to 800 aJ) range, where most celestial sources give off the bulk of their energy, can be stopped by a few sheets of paper; 90% of the photons in a beam of 3 keV (480 aJ) X-rays are absorbed by traveling through just 10 cm of air. A proportional counter

5120-409: Is to the lens, the further the image is from the lens. With diverging lenses, incoming parallel rays diverge after going through the lens, in such a way that they seem to have originated at a spot one focal length in front of the lens. This is the lens's front focal point. Rays from an object at a finite distance are associated with a virtual image that is closer to the lens than the focal point, and on

5248-476: The Book of Optics ( Kitab al-manazir ) in which he explored reflection and refraction and proposed a new system for explaining vision and light based on observation and experiment. He rejected the "emission theory" of Ptolemaic optics with its rays being emitted by the eye, and instead put forward the idea that light reflected in all directions in straight lines from all points of the objects being viewed and then entered

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5376-693: The "GOES I–M Databook" and the "GOES-N Series Databook" , respectively. The GOES-R series was built by Lockheed Martin with the first and second in the series, GOES-16 and -17, declared operational in early 2019. Following an equipment failure on GOES-17, it was replaced by GOES-18 in January 2023, with the former taken out of service to act as a backup. Boeing would have built and launched GOES-Q only if GOES-O or GOES-P had failed to be delivered on-orbit in good working order. Lombardi, Michael A.; Hanson, D. Wayne (March–April 2005). "The GOES Time Code Service, 1974-2004: A Retrospective" . Journal of Research of

5504-553: The Data Collection System , a ground-based meteorological platform satellite data collection and relay service. Other instruments on board the spacecraft are the SEM set, which consists of a magnetometer , an X-ray sensor, a high energy proton and alpha particle detector, and an energetic particles sensor. The GOES-N series (GOES-13 through GOES-15) spacecraft also have a sun-pointed extreme ultraviolet sensor. In addition,

5632-501: The Granat Observatory were four WATCH instruments that could localize bright sources in the 6 to 180 keV range to within 0.5° using a Rotation Modulation Collimator. Taken together, the instruments' three fields of view covered approximately 75% of the sky. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Explorer 81, images solar flares from soft X-rays to gamma rays (~3 keV to ~20 MeV). Its imaging capability

5760-607: The Nimrud lens . The ancient Romans and Greeks filled glass spheres with water to make lenses. These practical developments were followed by the development of theories of light and vision by ancient Greek and Indian philosophers, and the development of geometrical optics in the Greco-Roman world . The word optics comes from the ancient Greek word ὀπτική , optikē ' appearance, look ' . Greek philosophy on optics broke down into two opposing theories on how vision worked,

5888-687: The Types I, II, and III . The design most commonly used by X-ray astronomers is the Type I since it has the simplest mechanical configuration. In addition, the Type I design offers the possibility of nesting several telescopes inside one another, thereby increasing the useful reflecting area. The Wolter Type II is useful only as a narrow-field imager or as the optic for a dispersive spectrometer. The Wolter Type III has never been employed for X-ray astronomy. With respect to collimated optics, focusing optics allow: The mirrors can be made of ceramic or metal foil coated with

6016-591: The XRISM telescope, while ISRO has launched Aditya-L1 and XPoSat . The GOES 14 spacecraft carries on board a Solar X-ray Imager to monitor the Sun's X-rays for the early detection of solar flares, coronal mass ejections, and other phenomena that impact the geospace environment. It was launched into orbit on June 27, 2009, at 22:51 GMT from Space Launch Complex 37B at the Cape Canaveral Air Force Station . The Chinese Hard X-ray Modulation Telescope

6144-398: The classical electromagnetic description of light, however complete electromagnetic descriptions of light are often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics , treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics

6272-449: The emission theory , the idea that visual perception is accomplished by rays emitted by the eyes. He also commented on the parity reversal of mirrors in Timaeus . Some hundred years later, Euclid (4th–3rd century BC) wrote a treatise entitled Optics where he linked vision to geometry , creating geometrical optics . He based his work on Plato's emission theory wherein he described

6400-468: The intromission theory and the emission theory . The intromission approach saw vision as coming from objects casting off copies of themselves (called eidola) that were captured by the eye. With many propagators including Democritus , Epicurus , Aristotle and their followers, this theory seems to have some contact with modern theories of what vision really is, but it remained only speculation lacking any experimental foundation. Plato first articulated

6528-448: The superposition principle , which is a wave-like property not predicted by Newton's corpuscle theory. This work led to a theory of diffraction for light and opened an entire area of study in physical optics. Wave optics was successfully unified with electromagnetic theory by James Clerk Maxwell in the 1860s. The next development in optical theory came in 1899 when Max Planck correctly modelled blackbody radiation by assuming that

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6656-463: The surface normal , a line perpendicular to the surface at the point where the ray hits. The incident and reflected rays and the normal lie in a single plane, and the angle between the reflected ray and the surface normal is the same as that between the incident ray and the normal. This is known as the Law of Reflection . For flat mirrors , the law of reflection implies that images of objects are upright and

6784-571: The -West station by GOES-11. When GOES-10 was decommissioned on 1 December 2009, GOES-South was taken over by GOES-12. Since the retirement of GOES-12 on 16 August 2013, the GOES-South station has been unoccupied. GOES-16 has since made the need for a dedicated GOES-South satellite obsolete; as of 2019, the satellite produces full disk images every 10 minutes. In September 2006, NOAA reduced the planned number of GOES-R satellites from four to two because of cost overrun concerns. The planned delivery schedule

6912-554: The African . Bacon was able to use parts of glass spheres as magnifying glasses to demonstrate that light reflects from objects rather than being released from them. The first wearable eyeglasses were invented in Italy around 1286. This was the start of the optical industry of grinding and polishing lenses for these "spectacles", first in Venice and Florence in the thirteenth century, and later in

7040-590: The GOES satellites carry a search and rescue repeater that collects data from Emergency Position-Indicating Radio Beacons and Emergency Locator Transmitter beacons, which are used during search-and-rescue operations by the U.S. Air Force Rescue Coordination Center . The proposed instrument package for the GOES-R series initially included the following: In September 2006, the HES was cancelled. Before being launched, GOES satellites are designated by letters (A, B, C, etc.). Once

7168-456: The GOES-R series became operational, unless a satellite was dedicated to this continent, imagery of South America was updated every 3 hours instead of every 30 minutes. The GOES-South station was usually assigned to older satellites whose North American operations have been taken over by new satellites. For example, GOES-10 was moved from the GOES-West position to GOES-South after it was replaced in

7296-511: The GOES-West position at 135°W over the Pacific Ocean. It moved eastward to 128° W beginning on 29 October 2018 in order to make room for GOES-17 , which took over the GOES-West position on 10 December 2018. GOES-15 operated in tandem with GOES-17 for some time, but was retired in early 2020 and moved to a parking orbit. GOES-15 was temporarily returned to operational status in August 2020 to fill

7424-499: The GOES-West position at 137.2° W. The satellite, designated as GOES-S before orbiting, was launched by an Atlas V 541 rocket from Space Launch Complex 41 on 1 March 2018. Following post-launch testing and troubleshooting of a problem in its imager, the satellite was declared operational in February 2019. Several GOES satellites are still in orbit but are either inactive or have been re-purposed. Although GOES-3 ceased to be used for weather operations in 1989, it spent over 20 years as

7552-548: The Huygens–Fresnel principle states that every point of a wavefront is associated with the production of a new disturbance, it is possible for a wavefront to interfere with itself constructively or destructively at different locations producing bright and dark fringes in regular and predictable patterns. Interferometry is the science of measuring these patterns, usually as a means of making precise determinations of distances or angular resolutions . The Michelson interferometer

7680-605: The SESC. The main mission of a GOES satellite is carried out by the primary payload instruments, which are the Imager and the Sounder. The Imager is a multichannel instrument that senses infrared radiant energy and visible reflected solar energy from the Earth's surface and atmosphere. The Sounder provides data for vertical atmospheric temperature and moisture profiles, surface and cloud top temperature, and ozone distribution. GOES also offers

7808-584: The US portion of the Apollo–Soyuz mission (July 1975), and on French TOURNESOL instrument. Monitoring generally means to be aware of the state of a system. A device that displays or sends a signal for displaying X-ray output from an X-ray generating source so as to be aware of the state of the source is referred to as an X-ray monitor in space applications. On Apollo 15 in orbit above the Moon , for example, an X-ray monitor

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7936-473: The X-ray mirror for the NuSTAR telescope pushed this up to 79 keV light. To reflect at this level, glass layers were multi-coated with tungsten (W)/ silicon (Si) or platinum (Pt)/ silicon carbide (SiC). While earlier X-ray telescopes were using simple collimating techniques (e.g. rotating collimators, wire collimators), the technology most used in the present day employs coded aperture masks. This technique uses

8064-473: The X-ray telescope onboard OSO 4 consisted of a single thin NaI(Tl) scintillation crystal plus phototube assembly enclosed in a CsI(Tl) anti-coincidence shield. OSO 5 carried a CsI crystal scintillator. The central crystal was 0.635 cm thick, had a sensitive area of 70 cm, and was viewed from behind by a pair of photomultiplier tubes. The PHEBUS had two independent detectors, each detector consisted of

8192-484: The amplitude of the wave, which for light is associated with a brightening of the waveform in that location. Alternatively, if the two waves of the same wavelength and frequency are out of phase, then the wave crests will align with wave troughs and vice versa. This results in destructive interference and a decrease in the amplitude of the wave, which for light is associated with a dimming of the waveform at that location. See below for an illustration of this effect. Since

8320-542: The angle of incidence. Plutarch (1st–2nd century AD) described multiple reflections on spherical mirrors and discussed the creation of magnified and reduced images, both real and imaginary, including the case of chirality of the images. During the Middle Ages , Greek ideas about optics were resurrected and extended by writers in the Muslim world . One of the earliest of these was Al-Kindi ( c.  801 –873) who wrote on

8448-435: The angles between the normal (to the interface) and the incident and refracted waves, respectively. The index of refraction of a medium is related to the speed, v , of light in that medium by n = c / v , {\displaystyle n=c/v,} where c is the speed of light in vacuum . Snell's Law can be used to predict the deflection of light rays as they pass through linear media as long as

8576-449: The distance (as if on the surface of a pool of water). Optical materials with varying indexes of refraction are called gradient-index (GRIN) materials. Such materials are used to make gradient-index optics . For light rays travelling from a material with a high index of refraction to a material with a low index of refraction, Snell's law predicts that there is no θ 2 when θ 1 is large. In this case, no transmission occurs; all

8704-677: The earlier Synchronous Meteorological Satellites (SMS) generation. Following the three SMS GOES spacecraft, five satellites were procured from Hughes , which became the first generation GOES satellites. Four of these reached orbit, with GOES-G being lost in a launch failure. The next five GOES satellites were constructed by Space Systems/Loral , under contract to NASA. The imager and sounder instruments were produced by ITT Aerospace/Communication Division. GOES-8 and -9 were designed to operate for three years, while -10, -11 and -12 have expected lifespans of five years. GOES-11 and -12 were launched carrying enough fuel for ten years of operation, in

8832-451: The eastern and western halves of the U.S., respectively. GOES-East is occupied by GOES-16, while GOES-West is occupied by GOES-17. The -East/-West designation is used more frequently than the satellite's number designation. GOES-IO ( Indian Ocean ), a new designation revealed in early May 2020, is currently occupied by GOES-13 (DOD-1). There was also a GOES-South position, which is meant to provide dedicated coverage of South America. Before

8960-489: The electromagnetic radiation emitted by X-ray tubes had a longer wavelength than the radiation emitted by radioactive nuclei (gamma rays). So older literature distinguished between X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10 m, defined as gamma rays. However, as shorter wavelength continuous spectrum "X-ray" sources such as linear accelerators and longer wavelength "gamma ray" emitters were discovered,

9088-523: The event that they survived beyond their expected lifespan. A contract to develop four third-generation GOES satellites was awarded to Hughes Corporation , with the satellites scheduled for launch on Delta III rockets between 2002 and 2010. After a merger with Hughes, Boeing took over the development contracts, with launches transferred to the Delta IV , following the Delta III's retirement. The contract for

9216-426: The exchange of energy between light and matter only occurred in discrete amounts he called quanta . In 1905, Albert Einstein published the theory of the photoelectric effect that firmly established the quantization of light itself. In 1913, Niels Bohr showed that atoms could only emit discrete amounts of energy, thus explaining the discrete lines seen in emission and absorption spectra . The understanding of

9344-574: The eye, although he was unable to correctly explain how the eye captured the rays. Alhazen's work was largely ignored in the Arabic world but it was anonymously translated into Latin around 1200 A.D. and further summarised and expanded on by the Polish monk Witelo making it a standard text on optics in Europe for the next 400 years. In the 13th century in medieval Europe, English bishop Robert Grosseteste wrote on

9472-535: The feud between the two lasted until Hooke's death. In 1704, Newton published Opticks and, at the time, partly because of his success in other areas of physics, he was generally considered to be the victor in the debate over the nature of light. Newtonian optics was generally accepted until the early 19th century when Thomas Young and Augustin-Jean Fresnel conducted experiments on the interference of light that firmly established light's wave nature. Young's famous double slit experiment showed that light followed

9600-474: The focus to be smeared out in space. In particular, spherical mirrors exhibit spherical aberration . Curved mirrors can form images with a magnification greater than or less than one, and the magnification can be negative, indicating that the image is inverted. An upright image formed by reflection in a mirror is always virtual, while an inverted image is real and can be projected onto a screen. Refraction occurs when light travels through an area of space that has

9728-483: The fourth satellite, GOES-Q, was later cancelled. The first third-generation satellite, GOES-13, was launched in May 2006, originally serving as an on-orbit backup. However, in April 2010, GOES-12 was moved to South America coverage and GOES-13 was moved to the GOES-East role. Third generation satellites have an expected lifespan of seven years, but will carry excess fuel to allow them to operate for longer if possible, as with

9856-411: The gloss of surfaces such as mirrors, which reflect light in a simple, predictable way. This allows for the production of reflected images that can be associated with an actual ( real ) or extrapolated ( virtual ) location in space. Diffuse reflection describes non-glossy materials, such as paper or rock. The reflections from these surfaces can only be described statistically, with the exact distribution of

9984-416: The incident rays came. This is called retroreflection . Mirrors with curved surfaces can be modelled by ray tracing and using the law of reflection at each point on the surface. For mirrors with parabolic surfaces , parallel rays incident on the mirror produce reflected rays that converge at a common focus . Other curved surfaces may also focus light, but with aberrations due to the diverging shape causing

10112-418: The indexes of refraction and the geometry of the media are known. For example, the propagation of light through a prism results in the light ray being deflected depending on the shape and orientation of the prism. In most materials, the index of refraction varies with the frequency of the light, known as dispersion . Taking this into account, Snell's Law can be used to predict how a prism will disperse light into

10240-499: The instrument. X-ray telescopes were first used for astronomy to observe the Sun , which was the only source in the sky bright enough in X-rays for those early telescopes to detect. Because the Sun is so bright in X-rays, early X-ray telescopes could use a small focusing element and the X-rays would be detected with photographic film. The first X-ray picture of the Sun from a rocket-borne telescope

10368-436: The interaction between light and matter that followed from these developments not only formed the basis of quantum optics but also was crucial for the development of quantum mechanics as a whole. The ultimate culmination, the theory of quantum electrodynamics , explains all optics and electromagnetic processes in general as the result of the exchange of real and virtual photons. Quantum optics gained practical importance with

10496-426: The interaction of light with the material. For instance, the behaviour of a light wave interacting with a metal surface is quite different from what happens when it interacts with a dielectric material. A vector model must also be used to model polarised light. Numerical modeling techniques such as the finite element method , the boundary element method and the transmission-line matrix method can be used to model

10624-477: The invention of the compound optical microscope around 1595, and the refracting telescope in 1608, both of which appeared in the spectacle making centres in the Netherlands. In the early 17th century, Johannes Kepler expanded on geometric optics in his writings, covering lenses, reflection by flat and curved mirrors, the principles of pinhole cameras , inverse-square law governing the intensity of light, and

10752-491: The inventions of the maser in 1953 and of the laser in 1960. Following the work of Paul Dirac in quantum field theory , George Sudarshan , Roy J. Glauber , and Leonard Mandel applied quantum theory to the electromagnetic field in the 1950s and 1960s to gain a more detailed understanding of photodetection and the statistics of light. Classical optics is divided into two main branches: geometrical (or ray) optics and physical (or wave) optics. In geometrical optics, light

10880-466: The last two-second generation satellites. The fourth-generation satellites, the GOES-R series, were built by Lockheed Martin using the A2100 satellite bus . The GOES-R series is a four-satellite program (GOES-R, -S, -T and -U) intended to extend the availability of the operational GOES satellite system through 2036. GOES-R launched on 19 November 2016. It was renamed GOES-16 upon reaching orbit. Second of

11008-502: The launch of SMS-1 in 1974, have been a basic element of U.S. weather monitoring and forecasting. The procurement, design, and manufacture of GOES satellites is overseen by NASA . NOAA is the official provider of both GOES terrestrial data and GOES space weather data. Data can also be accessed using the SPEDAS software. The first GOES satellite, GOES-1, was launched in October 1975. Two more followed, launching almost two minutes short of

11136-504: The laws of reflection and refraction at interfaces between different media. These laws were discovered empirically as far back as 984 AD and have been used in the design of optical components and instruments from then until the present day. They can be summarised as follows: When a ray of light hits the boundary between two transparent materials, it is divided into a reflected and a refracted ray. The laws of reflection and refraction can be derived from Fermat's principle which states that

11264-449: The light is modelled as a collection of particles called " photons ". Quantum optics deals with the application of quantum mechanics to optical systems. Optical science is relevant to and studied in many related disciplines including astronomy , various engineering fields, photography , and medicine (particularly ophthalmology and optometry , in which it is called physiological optics). Practical applications of optics are found in

11392-422: The light is reflected. This phenomenon is called total internal reflection and allows for fibre optics technology. As light travels down an optical fibre, it undergoes total internal reflection allowing for essentially no light to be lost over the length of the cable. A device that produces converging or diverging light rays due to refraction is known as a lens . Lenses are characterized by their focal length :

11520-443: The mathematical rules of perspective and described the effects of refraction qualitatively, although he questioned that a beam of light from the eye could instantaneously light up the stars every time someone blinked. Euclid stated the principle of shortest trajectory of light, and considered multiple reflections on flat and spherical mirrors. Ptolemy , in his treatise Optics , held an extramission-intromission theory of vision:

11648-489: The merits of Aristotelian and Euclidean ideas of optics, favouring the emission theory since it could better quantify optical phenomena. In 984, the Persian mathematician Ibn Sahl wrote the treatise "On burning mirrors and lenses", correctly describing a law of refraction equivalent to Snell's law. He used this law to compute optimum shapes for lenses and curved mirrors . In the early 11th century, Alhazen (Ibn al-Haytham) wrote

11776-483: The north–south direction). This usually ends the satellite's primary mission. However, when the inclination is high enough the satellite may begin to rise above the polar horizons at the extremes of the figure-8, as was the case for GOES-3. A nine-meter dish was constructed at the station, and communication with the satellite could be obtained for about five hours per day. Data rates were around 2.048 megabytes/second (bi-directional) under optimum conditions. GOES-8 , which

11904-405: The object and image distances are positive if the object and image are on opposite sides of the lens. Incoming parallel rays are focused by a converging lens onto a spot one focal length from the lens, on the far side of the lens. This is called the rear focal point of the lens. Rays from an object at a finite distance are focused further from the lens than the focal distance; the closer the object

12032-401: The optical explanations of astronomical phenomena such as lunar and solar eclipses and astronomical parallax . He was also able to correctly deduce the role of the retina as the actual organ that recorded images, finally being able to scientifically quantify the effects of different types of lenses that spectacle makers had been observing over the previous 300 years. After the invention of

12160-676: The path taken between two points by a ray of light is the path that can be traversed in the least time. Geometric optics is often simplified by making the paraxial approximation , or "small angle approximation". The mathematical behaviour then becomes linear, allowing optical components and systems to be described by simple matrices. This leads to the techniques of Gaussian optics and paraxial ray tracing , which are used to find basic properties of optical systems, such as approximate image and object positions and magnifications . Reflections can be divided into two types: specular reflection and diffuse reflection . Specular reflection describes

12288-511: The propagation of light in systems which cannot be solved analytically. Such models are computationally demanding and are normally only used to solve small-scale problems that require accuracy beyond that which can be achieved with analytical solutions. All of the results from geometrical optics can be recovered using the techniques of Fourier optics which apply many of the same mathematical and analytical techniques used in acoustic engineering and signal processing . Gaussian beam propagation

12416-416: The rays (or flux) from the eye formed a cone, the vertex being within the eye, and the base defining the visual field. The rays were sensitive, and conveyed information back to the observer's intellect about the distance and orientation of surfaces. He summarized much of Euclid and went on to describe a way to measure the angle of refraction , though he failed to notice the empirical relationship between it and

12544-423: The reflected light depending on the microscopic structure of the material. Many diffuse reflectors are described or can be approximated by Lambert's cosine law , which describes surfaces that have equal luminance when viewed from any angle. Glossy surfaces can give both specular and diffuse reflection. In specular reflection, the direction of the reflected ray is determined by the angle the incident ray makes with

12672-415: The same distance behind the mirror as the objects are in front of the mirror. The image size is the same as the object size. The law also implies that mirror images are parity inverted, which we perceive as a left-right inversion. Images formed from reflection in two (or any even number of) mirrors are not parity inverted. Corner reflectors produce reflected rays that travel back in the direction from which

12800-407: The same side of the lens as the object. The closer the object is to the lens, the closer the virtual image is to the lens. As with mirrors, upright images produced by a single lens are virtual, while inverted images are real. Lenses suffer from aberrations that distort images. Monochromatic aberrations occur because the geometry of the lens does not perfectly direct rays from each object point to

12928-411: The sensors to "stare" at the Earth and thus more frequently image clouds, monitor the Earth's surface temperature and water vapour fields, and sound the atmosphere for its vertical thermal and vapor structures. The evolution of atmospheric phenomena can be followed, ensuring real-time coverage of meteorological events such as severe local storms and tropical cyclones . The importance of this capability

13056-398: The series GOES-S, was launched on 1 March 2018. It was renamed GOES-17 upon reaching orbit. Four GOES satellites are available for operational use. GOES-14 is in storage at 105° W. The launch of this satellite, which was designated GOES-O before orbiting, was delayed several times. It was launched successfully on 27 June 2009 from Space Launch Complex 37, on a Delta IV Medium rocket,

13184-421: The signal. X-rays has a huge span in wavelength (~8 nm - 8 pm), frequency (~50 PHz - 50 EHz) and energy (~0.12 - 120 keV). In terms of temperature, 1 eV = 11,604 K. Thus X-rays (0.12 to 120 keV) correspond to 1.39 × 10 to 1.39 × 10 K. From 10 to 0.1 nanometers (nm) (about 0.12 to 12 keV ) they are classified as soft X-rays, and from 0.1 nm to 0.01 nm (about 12 to 120 keV) as hard X-rays. Closer to

13312-405: The simple equation 1 S 1 + 1 S 2 = 1 f , {\displaystyle {\frac {1}{S_{1}}}+{\frac {1}{S_{2}}}={\frac {1}{f}},} where S 1 is the distance from the object to the lens, θ 2 is the distance from the lens to the image, and f is the focal length of the lens. In the sign convention used here,

13440-464: The spectacle making centres in both the Netherlands and Germany. Spectacle makers created improved types of lenses for the correction of vision based more on empirical knowledge gained from observing the effects of the lenses rather than using the rudimentary optical theory of the day (theory which for the most part could not even adequately explain how spectacles worked). This practical development, mastery, and experimentation with lenses led directly to

13568-444: The superposition principle can be used to predict the shape of interacting waveforms through the simple addition of the disturbances. This interaction of waves to produce a resulting pattern is generally termed "interference" and can result in a variety of outcomes. If two waves of the same wavelength and frequency are in phase , both the wave crests and wave troughs align. This results in constructive interference and an increase in

13696-496: The system work together to provide a continuous stream of environmental data. The National Weather Service (NWS) and the Meteorological Service of Canada use the GOES system for their North American weather monitoring and forecasting operations, and scientific researchers use the data to better understand land, atmosphere, ocean, and climate dynamics. The GOES system uses geosynchronous equatorial satellites that, since

13824-467: The telescope, Kepler set out the theoretical basis on how they worked and described an improved version, known as the Keplerian telescope , using two convex lenses to produce higher magnification. Optical theory progressed in the mid-17th century with treatises written by philosopher René Descartes , which explained a variety of optical phenomena including reflection and refraction by assuming that light

13952-440: The term "light" is also often applied to infrared (0.7–300 μm) and ultraviolet radiation (10–400 nm). The wave model can be used to make predictions about how an optical system will behave without requiring an explanation of what is "waving" in what medium. Until the middle of the 19th century, most physicists believed in an "ethereal" medium in which the light disturbance propagated. The existence of electromagnetic waves

14080-589: The visible range of the electromagnetic spectrum is the ultraviolet . The draft ISO standard on determining solar irradiances (ISO-DIS-21348) describes the ultraviolet as ranging from ~10 nm to ~400 nm. That portion closest to X-rays is often referred to as the "extreme ultraviolet" ( EUV or XUV). When an EUV photon is absorbed, photoelectrons and secondary electrons are generated by ionization , much like what happens when X-rays or electron beams are absorbed by matter. The distinction between X-rays and gamma rays has changed in recent decades. Originally,

14208-462: The wavelength bands largely overlapped. The two types of radiation are now usually distinguished by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus . Although the more energetic X-rays, photons with an energy greater than 30 keV (4,800 a J), can penetrate the Earth's atmosphere at least for distances of a few meters, the Earth's atmosphere

14336-443: Was 200 microseconds . The X-ray spectrometer aboard ISEE-3 was designed to study both solar flares and cosmic gamma-ray bursts over the energy range 5-228 keV. The experiment consisted of 2 cylindrical X-ray detectors: a Xenon filled proportional counter covering 5-14 keV, and a NaI(Tl) scintillator covering 12-1250 keV. Most existing X-ray telescopes use CCD detectors, similar to those in visible-light cameras. In visible-light,

14464-400: Was a famous instrument which used interference effects to accurately measure the speed of light. The appearance of thin films and coatings is directly affected by interference effects. Antireflective coatings use destructive interference to reduce the reflectivity of the surfaces they coat, and can be used to minimise glare and unwanted reflections. The simplest case is a single layer with

14592-401: Was also slowed down to reduce costs. The expected cost of the series is $ 7.69 billion, a $ 670 million increase from the prior $ 7 billion estimate. The contract for constructing the satellites and manufacturing the magnetometer, SUVI, and GLM was awarded to Lockheed Martin. This award was challenged by losing bidder Boeing; however, the protest was subsequently dismissed. The ABI instrument

14720-570: Was delivered by L3Harris (formerly ITT Exelis ). The SEISS was delivered by Assurance Technology Corporation. XRS and EUVS are being combined into the Extreme Ultra Violet and X-Ray Irradiance Sensors (EXIS), which was delivered by the Laboratory for Atmospheric and Space Physics of the University of Colorado . The contract for the ground system, including data processing, was awarded to

14848-400: Was designated GOES-I before orbiting, was the GOES-East satellite when it was in operation. It is in a parking orbit and is drifting westerly at a rate of about 4° daily. It was decommissioned on 1 April 2003 and deactivated on 5 May 2004 after the failure of its propulsion system. GOES-10 , which was designated GOES-K before orbiting, was decommissioned on 2 December 2009 and was boosted to

14976-472: Was designated GOES-N before orbiting, was decommissioned on 3 January 2018 and boosted into storage orbit. It was transferred to the U.S. Space Force and positioned at 61.5ºE under the new name EWS-G1. Following three years of monitoring the Indian Ocean, EWS-G1 was retired on 31 October 2023 when EWS-G2 (formerly GOES-15) took over. GOES-15 , which was designated GOES-P before orbiting, was launched successfully on 4 March 2010. From 2011 to 2018, it occupied

15104-540: Was emitted by objects which produced it. This differed substantively from the ancient Greek emission theory. In the late 1660s and early 1670s, Isaac Newton expanded Descartes's ideas into a corpuscle theory of light , famously determining that white light was a mix of colours that can be separated into its component parts with a prism . In 1690, Christiaan Huygens proposed a wave theory for light based on suggestions that had been made by Robert Hooke in 1664. Hooke himself publicly criticised Newton's theories of light and

15232-529: Was launched on 27 July 2022 as a technology demonstrator for Einstein Probe , launched on January 9, 2024, dedicated to time-domain high-energy astrophysics . The Space Variable Objects Monitor observatory launched on 22 June 2024 is directed towards studying the explosions of massive stars and analysis of gamma-ray bursts . A soft X-ray solar imaging telescope is on board the GOES-13 weather satellite launched using

15360-454: Was launched on June 15, 2017 to observe black holes, neutron stars, active galactic nuclei and other phenomena based on their X-ray and gamma-ray emissions. The Lobster-Eye X-ray Satellite was launched on 25 July 2020 by CNSA making it is the first in-orbit telescope to utilize the lobster-eye imaging technology of ultra-large field of view imaging to search for dark matter signals in the x-ray energy range. Lobster Eye Imager for Astronomy

15488-522: Was originally proposed in 1960 by Riccardo Giacconi and Bruno Rossi , the founders of extrasolar X-ray astronomy. This type of mirror is often used as the primary reflector in an optical telescope. However, images of off-axis objects would be severely blurred. The German physicist Hans Wolter showed in 1952 that the reflection off a combination of two elements, a paraboloid followed by a hyperboloid, would work far better for X-ray astronomy applications. Wolter described three different imaging configurations,

15616-467: Was predicted in 1865 by Maxwell's equations . These waves propagate at the speed of light and have varying electric and magnetic fields which are orthogonal to one another, and also to the direction of propagation of the waves. Light waves are now generally treated as electromagnetic waves except when quantum mechanical effects have to be considered. Many simplified approximations are available for analysing and designing optical systems. Most of these use

15744-527: Was proven during hurricanes Hugo (1989) and Andrew (1992). The GOES spacecraft also enhance operational services and improve support for atmospheric science research, numerical weather prediction models, and environmental sensor design and development. Satellite data is broadcast on the L-band , and received at the NOAA Command and Data Acquisition ground station at Wallops Island, Virginia from which it

15872-623: Was retired in early 2020 and moved to a parking orbit. GOES-15 was temporarily returned to operational status in August 2020 to fill a gap in the sensor capabilities of GOES-17 due to a hardware issue. GOES-16 occupies the GOES-East position at 75° W. This satellite, which was designated GOES-R before orbiting, was launched by an Atlas V 541 rocket from Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida on 19 November 2016. It underwent Post-Launch Testing through early 2017 before replacing GOES-13 as GOES-East. GOES-17 occupies

16000-456: Was returned to storage. GOES-15 , which was designated GOES-P before orbiting, was launched successfully on 4 March 2010, on a Delta IV M+ (4,2) . From 2011 to 2018, it occupied the GOES-West position at 135°W over the Pacific Ocean. It moved eastward to 128° W beginning on 29 October 2018 in order to make room for GOES-17 , which took over the GOES-West position on 10 December 2018. GOES-15 operated in tandem with GOES-17 for some time, but

16128-560: Was taken by John V. Lindsay of the NASA Goddard Space Flight Center and collaborators in 1963. The first orbiting X-ray telescope flew on Skylab in the early 1970s and recorded more than 35,000 full-disk images of the Sun over a 9-month period. First specialised X-ray satellite, Uhuru , was launched by NASA in 1970. It detected 339 X-ray sources in its 2.5-year lifetime. The Einstein Observatory , launched in 1978,

16256-420: Was the first imaging X-ray observatory. It obtained high-resolution X-ray images in the energy range from 0.1 to 4 keV of stars of all types, supernova remnants, galaxies, and clusters of galaxies. Another large project was ROSAT (active from 1990 to 1999), which was a heavy X-ray space observatory with focusing X-ray optics, and European EXOSAT . The Chandra X-Ray Observatory was launched by NASA in 1999 and

16384-514: Was used to follow the possible variation in solar X-ray intensity and spectral shape while mapping the lunar surface with respect to its chemical composition due to the production of secondary X-rays . The X-ray monitor of Solwind , designated NRL-608 or XMON, was a collaboration between the Naval Research Laboratory and Los Alamos National Laboratory . The monitor consisted of 2 collimated argon proportional counters. A scintillator

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