The Extreme ultraviolet Imaging Telescope (EIT) is an instrument on the SOHO spacecraft used to obtain high-resolution images of the solar corona in the ultraviolet range. The EIT instrument is sensitive to light of four different wavelengths: 17.1, 19.5, 28.4, and 30.4 nm, corresponding to light produced by highly ionized iron (XI)/(X), (XII), (XV), and helium (II), respectively. EIT is built as a single telescope with a quadrant structure to the entrance mirrors: each quadrant reflects a different color of EUV light, and the wavelength to be observed is selected by a shutter that blocks light from all but the desired quadrant of the main telescope. The Bastille Day Flare at the 19. ... Categories: Stub ... A nanometre (American spelling: nanometer) is 1. ... The wavelength is the distance between repeating units of a wave pattern. ... Captain Nemo and Professor Aronnax contemplating measuring instruments in Twenty Thousand Leagues Under the Sea In physics and engineering, measurement is the activity of comparing physical quantities of real-world objects and events. ... The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on 2 December 1995 to study the sun, and began normal operations in May 1996. ... A spacecraft is a vehicle, vessel, craft or device designed to operate beyond the surface of the Earth in outer space. ... In common usage, an image (from Latin imago) or picture is an artifact that reproduces the likeness of some subject—usually a physical object or a person. ... For other uses, see Sun (disambiguation). ... In astronomy, a corona is the luminous plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... The solar corona as seen in deep ultraviolet light at 17. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength[1]. The elementary particle that defines light is the photon. ... The wavelength is the distance between repeating units of a wave pattern. ... A nanometre (American spelling: nanometer) is 1. ... An ion is an atom or group of atoms that normally are electrically neutral and achieve their status as an ion by loss or addition of one or more electrons. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ...

The EIT wavelengths are of great interest to solar physicists because they are emitted by the very hot solar corona but not by the relatively cooler photosphere of the Sun; this reveals structures in the corona that would otherwise be obscured by the brightness of the Sun itself. EIT was originally conceived as a viewfinder instrument to help select observing targets for the other instruments on board SOHO, but EIT is credited with a good fraction of the original science to come from SOHO, including the first observations of traveling wave phenomena in the corona, characterization of coronal mass ejection onset, and determination of the structure of coronal holes. It currently (2006) produces an Fe XII (19.5 nm wavelength) image of the Sun about four times an hour, around the clock; these are immediately uplinked as time-lapse movies to the SOHO web site for immediate viewing by anyone who is interested. The images are used for long-duration studies of the Sun, for detailed structural analyses of solar features, and for real-time space weather prediction by the NOAA Space Environment Center. The corona is the luminous plasma atmosphere of the Sun extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... The photosphere of an astronomical object is the region at which the optical depth becomes one for a photon of wavelength equal to 5000 angstroms. ... In photography a viewfinder is what the photographer looks through to compose, and in many cases to focus, the picture. ... A composite image showing two CMEs (at 2 oclock and 8 oclock), with the sun at center. ... Aurora australis observed by Discovery, May 1991 Space weather is the concept of changing environmental conditions in outer space. ... The National Oceanic and Atmospheric Administration (NOAA) is a scientific agency of the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. ... The Space Environment Center (SEC) is a laboratory in the National Oceanic and Atmospheric Administration (NOAA)/Office of Oceanic and Atmospheric Research (OAR). ...

Technology

EIT is the first long-duration instrument to use normal incidence multilayer coated optics to image the Sun in extreme ultraviolet. This portion of the spectrum is extremely difficult to reflect, as most matter absorbs the light very strongly. Conventionally these wavelengths have been reflected either using grazing incidence (as in a Wolter telescope for imaging X-rays) or a diffraction grating (as in the infamous overlappograph flown on Skylab in the mid 1970s). Modern vacuum deposition technology allows mirrors to be coated with extremely thin layers of nearly any material. The multilayer mirrors in an EUV telescope are coated with alternate layers of a light "spacer" element (such as silicon) that absorbs EUV light only weakly, and a heavy "scatterer" element (such as molybdenum) that absorbs EUV light very strongly. Perhaps 100 layers of each type might be placed on the mirror, with a thickness of around 10 nm each! The layer thickness is tightly controlled, so that at the desired wavelength, reflected photons from each layer interfere constructively. In this way, reflectivities of up to ~50% can be attained. Fig. ... Table of Opticks, 1728 Cyclopaedia Optics ( appearance or look in ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. ... For other uses, see Sun (disambiguation). ... The solar corona as seen in deep ultraviolet light at 17. ... This article or section does not cite its references or sources. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... To meet Wikipedias quality standards, this article or section may require cleanup. ... Drawing of Skylab with components labelled Skylab was the first space station the United States launched into orbit. ... The 1970s decade refers to the years from 1970 to 1979, inclusive. ... Vacuum deposition is a process used to create a thin layer of a substance (a coating) on a solid object (the substrate). ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark gray with bluish tinge Atomic mass 28. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ... A nanometre (American spelling: nanometer) is 1. ...

The multilayer technology allows conventional telescope forms (such as the Cassegrain or Ritchey-Chretien designs) to be used in a novel part of the spectrum. Solar imaging with multilayer EUV optics was pioneered in the 1990s by the MSSTA and NIXT sounding rockets, each of which flew on several five-minute missions into space. Multilayer EUV optics are also used in terrestrial nanolithography rigs for fabrication of microchips. Cassegrain may refer to the Cassegrain Reflector Laurent Cassegrain, catholic priest and teacher and probably the inventor of the Cassegrain Reflector Sieur Guillaume Cassegrain, French sculptur Categories: Disambiguation ... The Ritchey-Chrétien is a specialized Cassegrain reflector which has two hyperbolic mirrors (instead of a parabolic primary). ... This article is about the year. ... Sounding rocket 36. ... A sounding rocket, sometimes called an elevator research rocket, is an instrument-carrying suborbital rocket designed to take measurements and perform scientific experiments during its flight. ... Nanolithography — or lithography at the nanometer scale — refers to the fabrication of nanometer-scale structures, meaning patterns with at least one lateral dimension between the size of an individual atom and approximately 100 nm. ... Microchip can refer to: Microchip (or simply chip) is used rather loosely in electronics. ...

The EIT detector is a conventional CCDs that are back-illuminated and specially thinned to admit the EUV photons. Because the detector is about equally sensitive to EUV and visible photons, and the Sun is about one billion (10⁹) times brighter in visible light than in EUV, special thin foil filters are used to block the visible light while admitting the EUV. The filters are made of extremely thin aluminum foil, about 200 nm (0.2 micrometre) thick, and transmit about half of the incident EUV light while absorbing essentially all of the incident visible light. A specially developed CCD used for ultraviolet imaging in a wire bonded package. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ...

History

EIT was a difficult sell to the scientific funding agencies, as it was not clear in the early 1990s that simple imaging of the corona would be scientifically useful (most of the other instruments on board SOHO are spectrographs of various kinds). The EIT PI, Jean-Pierre Delaboudiniere, was forced to scrounge funding and resources from several locations to construct and launch the instrument. For example, EIT alone of the SOHO instruments does not have its own flight computer; it is connected to the LASCO instrument flight computer, and is treated operationally as an additional LASCO camera. No funding was available for a pointing adjustment mechanisms, so EIT is bolted directly to the spacecraft and hence forms the SOHO pointing reference: the other instruments all align themselves to the EIT images. Focus adjustment is achieved by thermal expansion: the internal survival heaters (found in most spaceborne instruments) are used to achieve microscopic changes in the size of the telescope structure and hence the mirror spacing. EIT was originally allocated only about 1 kbit/s of data -- about the same speed as a 110 baud teletype -- but after its utility became clear much more telemetry bandwidth was allocated to it. This article is about the year. ... For Acoustic uses in spectrographs of sound waves, see below. ... A principal investigator (PI) is the lead scientist for a particular well-defined science project, such as an astronomical observing campaign, laboratory study or clinical trial. ... In physics, thermal expansion is the tendency of matter to increase in volume or pressure when heated. ... In telecommunications and electronics, baud (pronounced , unit symbol Bd) is a measure of the symbol rate, that is the number of distinct symbolic changes (signalling event) made to the transmission medium per second in a digitally modulated signal. ... A teleprinter (teletypewriter, teletype or TTY) is a now largely obsolete electro-mechanical typewriter which can be used to communicate typed messages from point to point through a simple electrical communications channel, often just a pair of wires. ... Telemetry is a technology that allows the remote measurement and reporting of information of interest to the system designer or operator. ... This article or section does not cite its references or sources. ...

Related instruments

The technology in EIT is based on prototype instruments that were flown on the sounding rocket payloads MSSTA and NIXT. The first multilayer telescope to image the full disk of the Sun in EUV was flown by A.B.C. Walker and team in 1987. The TRACE spacecraft (launched into LEO in the late 1990s) carries a similar multilayer imager, as do the planned STEREO and Solar Dynamics Observatory missions. A sounding rocket, sometimes called an elevator research rocket, is an instrument-carrying suborbital rocket designed to take measurements and perform scientific experiments during its flight. ... Sounding rocket 36. ... Arthur Bertram Cuthbert Walker, Jr. ... 1987 (MCMLXXXVII) was a common year starting on Thursday of the Gregorian calendar. ... It has been suggested that this article or section be merged with Tracing. ... A low Earth orbit (LEO) is an orbit in which objects such as satellites are below intermediate circular orbit (ICO) and far below geostationary orbit, but typically around 350 - 1400 km above the Earths surface. ... Germans dancing on the Berlin Wall in late 1989, the symbol of the cold war divide falls down as the world unites in the 1990s. ... STEREO (Solar TErrestrial RElations Observatory) is a solar observation mission which was launched on 26 October 2006 at 00:52 GMT.[1] Two identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead and fall gradually behind the earth. ... The Solar Dynamics Observatory (SDO) is a NASA mission under the Living with a Star (LWS) program. ...

External links

• Latest EIT full-field images