Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

 launched on STS-93
STS-93 marked the 95th launch of the Space Shuttle, the 26th launch of Columbia, and the 21st night launch of a Space Shuttle. Eileen Collins became the first female shuttle Commander on this flight. Its primary payload was the Chandra X-ray Observatory. It would also be the last mission of...

 by NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 on July 23, 1999. It was named in honor of India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...

 Subrahmanyan Chandrasekhar
Subrahmanyan Chandrasekhar
Subrahmanyan Chandrasekhar, FRS ) was an Indian origin American astrophysicist who, with William A. Fowler, won the 1983 Nobel Prize for Physics for key discoveries that led to the currently accepted theory on the later evolutionary stages of massive stars...

 who is known for determining the maximum mass
Chandrasekhar limit
When a star starts running out of fuel, it usually cools off and collapses into one of three compact forms, depending on its total mass:* a White Dwarf, a big lump of Carbon and Oxygen atoms, almost like one huge molecule...

 for white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...

s. "Chandra
In Hinduism, Chandra is a lunar deity and a Graha. Chandra is also identified with the Vedic Lunar deity Soma . The Soma name refers particularly to the juice of sap in the plants and thus makes the Moon the lord of plants and vegetation. He is described as young, beautiful, fair; two-armed and...

" also means "moon" or "luminous" in Sanskrit
Sanskrit , is a historical Indo-Aryan language and the primary liturgical language of Hinduism, Jainism and Buddhism.Buddhism: besides Pali, see Buddhist Hybrid Sanskrit Today, it is listed as one of the 22 scheduled languages of India and is an official language of the state of Uttarakhand...


Chandra Observatory is the third of NASA's four Great Observatories
Great Observatories program
NASA's series of Great Observatories satellites are four large, powerful space-based telescopes. Each of the Great Observatories has had a similar size and cost at program outset, and each has made a substantial contribution to astronomy...

. The first was Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

; second the Compton Gamma Ray Observatory
Compton Gamma Ray Observatory
The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...

, launched in 1991; and last is the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...

. Prior to successful launch, the Chandra Observatory was known as AXAF, the Advanced X-ray Astrophysics Facility. AXAF was assembled and tested by TRW
TRW Inc. was an American corporation involved in a variety of businesses, mainly aerospace, automotive, and credit reporting. It was a pioneer in multiple fields including electronic components, integrated circuits, computers, software and systems engineering. TRW built many spacecraft,...

 (now Northrop Grumman
Northrop Grumman
Northrop Grumman Corporation is an American global aerospace and defense technology company formed by the 1994 purchase of Grumman by Northrop. The company was the fourth-largest defense contractor in the world as of 2010, and the largest builder of naval vessels. Northrop Grumman employs over...

 Aerospace Systems) in Redondo Beach
Redondo Beach, California
Redondo Beach is one of the three Beach Cities located in Los Angeles County, California, United States. The population was 66,748 at the 2010 census, up from 63,261 at the 2000 census. The city is located in the South Bay region of the greater Los Angeles area.Redondo Beach was originally part of...

, California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, due primarily to the high angular resolution of the Chandra mirrors.

Since the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 absorbs the vast majority of X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

s, they are not detectable from Earth-based telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

s, requiring a space-based telescope to make these observations.


In 1976 the Chandra X-ray Observatory (called AXAF at the time) was proposed to NASA by Riccardo Giacconi
Riccardo Giacconi
Riccardo Giacconi is an Italian/American Nobel Prize-winning astrophysicist who laid the foundations of X-ray astronomy. He is currently a professor at the Johns Hopkins University.- Biography :...

 and Harvey Tananbaum. Preliminary work began the following year at Marshall Space Flight Center
Marshall Space Flight Center
The George C. Marshall Space Flight Center is the U.S. government's civilian rocketry and spacecraft propulsion research center. The largest center of NASA, MSFC's first mission was developing the Saturn launch vehicles for the Apollo moon program...

 (MSFC) and the Smithsonian Astrophysical Observatory
Smithsonian Astrophysical Observatory
The Smithsonian Astrophysical Observatory is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory to form the Harvard-Smithsonian Center for Astrophysics .-History:The SAO was founded in 1890 by...

 (SAO). In the meantime, in 1978, NASA launched the first imaging X-ray telescope, Einstein
Einstein Observatory
Einstein Observatory was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories...

 (HEAO-2), into orbit. Work continued on the Chandra project through 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. Chandra's planned orbit was changed to an elliptical one, reaching one third of the way to the Moon's at its farthest point. This eliminated the possibility of improvement or repair by the space shuttle
Space Shuttle program
NASA's Space Shuttle program, officially called Space Transportation System , was the United States government's manned launch vehicle program from 1981 to 2011...

 but put the observatory above the Earth's radiation belts
Van Allen radiation belt
The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...

 for most of its orbit.

AXAF was renamed Chandra in 1998 and launched in 1999 by the shuttle Columbia
Space Shuttle Columbia
Space Shuttle Columbia was the first spaceworthy Space Shuttle in NASA's orbital fleet. First launched on the STS-1 mission, the first of the Space Shuttle program, it completed 27 missions before being destroyed during re-entry on February 1, 2003 near the end of its 28th, STS-107. All seven crew...

 (STS-93). At 22753 kg, it was the heaviest payload ever launched by the shuttle, a consequence of the two-stage Inertial Upper Stage
Inertial Upper Stage
The Inertial Upper Stage , originally known as the Interim Upper Stage, is a two-stage solid-fueled booster rocket developed by the U.S...

 booster rocket system needed to transport the spacecraft to its high orbit.

Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in Cambridge, Massachusetts
Cambridge, Massachusetts
Cambridge is a city in Middlesex County, Massachusetts, United States, in the Greater Boston area. It was named in honor of the University of Cambridge in England, an important center of the Puritan theology embraced by the town's founders. Cambridge is home to two of the world's most prominent...

, with assistance from MIT and Northrop Grumman
Northrop Grumman
Northrop Grumman Corporation is an American global aerospace and defense technology company formed by the 1994 purchase of Grumman by Northrop. The company was the fourth-largest defense contractor in the world as of 2010, and the largest builder of naval vessels. Northrop Grumman employs over...

 Space Technology. The ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the telescope's focal plane during passages.

Although Chandra was initially given an expected lifetime of 5 years, on 4 September 2001 NASA extended its lifetime to 10 years "based on the observatory's outstanding results." Physically Chandra could last much longer. A study performed at the Chandra X-ray Center indicated that the observatory could last at least 15 years. On 24 July 2008 the International X-ray Observatory
International X-ray Observatory
The International X-ray Observatory was a planned X-ray telescope from about 2008 to 2011 by NASA, ESA, and JAXA. In 2011, NASA pulled out and ESA is forking/rebooting the project as the ESA Advanced Telescope for High ENergy Astrophysics ., which is an L-class candidate within the ESA Cosmic...

, a joint project between ESA, NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 and JAXA, was proposed as the next major X-ray observatory but has now been cancelled . Its expected launch date would have been 2020.


The data gathered by Chandra have greatly advanced the field of X-ray astronomy
X-ray astronomy
X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and...

  • The first light image, of supernova remnant
    Supernova remnant
    A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...

     Cassiopeia A
    Cassiopeia A
    Cassiopeia A is a supernova remnant in the constellation Cassiopeia and the brightest astronomical radio source in the sky, with a flux density of 2720 Jy at 1 GHz. The supernova occurred approximately away in the Milky Way. The expanding cloud of material left over from the supernova is now...

    , gave astronomers their first glimpse of the compact object at the center of the remnant, probably a neutron star
    Neutron star
    A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

     or black hole
    Black hole
    A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

    . (Pavlov, et al., 2000)
  • In the Crab Nebula
    Crab Nebula
    The Crab Nebula  is a supernova remnant and pulsar wind nebula in the constellation of Taurus...

    , another supernova remnant, Chandra showed a never-before-seen ring around the central pulsar
    A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...

     and jets that had only been partially seen by earlier telescopes. (Weisskopf, et al., 2000)
  • The first X-ray emission was seen from the supermassive black hole
    Supermassive black hole
    A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...

    , Sagittarius A*, at the center
    Galactic Center
    The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...

     of the Milky Way
    Milky Way
    The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

    . (Baganoff, et al., 2001)
  • Chandra found much more cool gas
    Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

     than expected spiralling into the center of the Andromeda Galaxy
    Andromeda Galaxy
    The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...

  • Pressure fronts were observed in detail for the first time in Abell 2142
    Abell 2142
    Abell 2142, or A2142, is a huge, X-ray luminous galaxy cluster in the constellation Corona Borealis. It is the result of a still ongoing merger between two galaxy clusters. The combined cluster is six million light years across, contains hundreds of galaxies and enough gas to make a thousand more...

    , where clusters
    Galaxy cluster
    A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...

     of galaxies are merging.
  • The earliest images in X-rays of the shock wave
    Shock wave
    A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...

     of a supernova
    A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

     were taken of SN 1987A
    SN 1987A
    SN 1987A was a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs from Earth, approximately 168,000 light-years, close enough that it was visible to the naked eye. It could be seen from the Southern...

  • Chandra showed for the first time the shadow of a small galaxy
    A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

     as it is being cannibalized by a larger one, in an image of Perseus A.
  • A new type of black hole was discovered in galaxy M82
    Messier 82
    Messier 82 is the prototype nearby starburst galaxy about 12 million light-years away in the constellation Ursa Major...

    , mid-mass objects purported to be the missing link between stellar-sized black holes
    Stellar black hole
    A stellar black hole is a black hole formed by the gravitational collapse of a massive star. They have masses ranging from about 3 to several tens of solar masses...

     and supermassive black holes. (Griffiths, et al., 2000)
  • X-ray emission lines were associated for the first time with a gamma-ray burst, Beethoven Burst GRB 991216. (Piro, et al., 2000)
  • High school students, using Chandra data, discovered
    CXOU J061705.3+222127
    CXOU J061705.3+222127 is a neutron star. It was likely formed 30,000 years ago in the supernova that created the supernova remnant IC 443. It is travelling at approximately 800,000 km/h away from the site.-External links:...

     a neutron star in supernova remnant IC 443
    IC 443
    IC 443 is a Galactic supernova remnant in the constellation Gemini. On the plan of the sky, it is located near the star Eta Geminorum....

  • Observations by Chandra and BeppoSAX
    BeppoSAX was an Italian–Dutch satellite for X-ray astronomy which played a crucial role in resolving the origin of gamma-ray bursts , the most energetic events known in the universe...

     suggest that gamma-ray bursts occur in star-forming regions.
  • Chandra data suggested that RX J1856.5-3754
    RX J1856.5-3754
    RX J1856.5-3754 is a nearby neutron star in Corona Australis. It is believed to have been created by a supernova explosion of its companion star about one million years ago and is moving 108 km/s across the sky...

     and 3C58
    3C58 or 3C 58 is a pulsar and surrounding synchrotron nebula within the Milky Way that is possibly associated with the supernova SN 1181. There are, however, signs that indicate that it could be several thousand years old, and thus not associated with that supernova...

    , previously thought to be pulsars, might be even denser objects: quark star
    Quark star
    A quark star or strange star is a hypothetical type of exotic star composed of quark matter, or strange matter. These are ultra-dense phases of degenerate matter theorized to form inside particularly massive neutron stars....

    s. These results are still debated.
  • Sound waves from violent activity around a supermassive black hole
    Supermassive black hole
    A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...

     were observed in the Perseus Cluster
    Perseus Cluster
    The Perseus Cluster is a cluster of galaxies in the constellation Perseus. It has a recession speed of 5,366 km/s and a diameter of 863′...

  • TWA 5B, a brown dwarf
    Brown dwarf
    Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...

    , was seen orbiting a binary
    Binary star
    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

     system of Sun-like star
    A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

  • Nearly all stars on the main sequence
    Main sequence
    The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...

     are X-ray emitters. (Schmitt & Liefke, 2004)
  • The X-ray shadow of Titan
    Titan (moon)
    Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....

     was seen when it transitted
    Astronomical transit
    The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...

     the Crab Nebula.
  • X-ray emissions from materials falling from a protoplanetary disc into a star. (Kastner, et al., 2004)
  • Hubble constant measured to be 76.9 km/s/Mpc using Sunyaev-Zel'dovich effect
    Sunyaev-Zel'dovich effect
    The Sunyaev–Zel'dovich effect is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which the low energy CMB photons receive energy boost during collision with the high energy cluster electrons...

  • 2006 Chandra found strong evidence that dark matter exists by observing supercluster collision
  • 2006 X-ray emitting loops, rings and filaments discovered around a supermassive black hole
    Supermassive black hole
    A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...

     within Messier 87
    Messier 87
    Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...

     imply the presence of pressure waves, shock waves and sound waves. The evolution of Messier 87
    Messier 87
    Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...

     may have been dramatically affected.
  • Observations of the Bullet cluster
    Bullet cluster
    The Bullet cluster consists of two colliding clusters of galaxies. Studies of the Bullet cluster, announced in August 2006, provide the best evidence to date for the existence of dark matter...

     put limits on the cross-section of the self-interaction of dark matter
    Dark matter
    In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...

  • "The Hand of God" photograph of PSR B1509-58
    PSR B1509-58
    PSR B1509-58 is a pulsar approximately 17,000 light-years away in the constellation of Circinus discovered by the Einstein X-Ray Observatory in 1982 . It is approximately 1700 years old and sits in a nebula that spans about 150 light years...


Technical description

Unlike optical telescopes which possess simple aluminized parabolic
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...

 surfaces (mirrors), X-ray telescopes generally use a Wolter telescope
Wolter telescope
A Wolter telescope is a telescope for X-rays using only grazing incidence optics. Visible light telescopes are built with lenses or parabolic mirrors at nearly normal incidence. Neither works well for X-rays. Lenses for visible light are made of a transparent material with an index of refraction...

 consisting of nested cylindrical paraboloid
In mathematics, a paraboloid is a quadric surface of special kind. There are two kinds of paraboloids: elliptic and hyperbolic. The elliptic paraboloid is shaped like an oval cup and can have a maximum or minimum point....

 and hyperboloid surfaces coated with iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...

 or gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

. X-ray photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

s would be absorbed by normal mirror surfaces, so mirrors with a low grazing angle are necessary to reflect them. Chandra uses four pairs of nested mirrors, together with their support structure, called the High Resolution Mirror Assembly (HRMA); the mirror substrate is 2 cm-thick glass, with the reflecting surface a 33 nm iridium coating, and the diameters are 65 cm, 87 cm, 99 cm and 123 cm. The thick substrate and particularly careful polishing allowed a very precise optical surface, which is responsible for Chandra's unmatched resolution: between 80% and 95% of the incoming X-ray energy is focused into a one-arcsecond circle. However, the thickness of the substrates limit the proportion of the aperture which is filled, leading to the low collecting area compared to XMM-Newton
The XMM-Newton is an orbiting X-ray observatory launched by ESA in December 1999 on a Ariane 5 rocket...


Chandra's highly elliptical
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...

 orbit allows it to observe continuously for up to 55 hours of its 65 hour orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...

. At its furthest orbital point from earth, Chandra is one of the furthest from earth earth-orbiting satellites. This orbit takes it beyond the geostationary satellites and beyond the outer Van Allen belt.

With an angular resolution
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...

 of 0.5 arcsecond (2.4 µrad), Chandra possesses a resolution over one thousand times better than that of the first orbiting X-ray telescope.


The Science Instrument Module (SIM) holds the two focal plane instruments, the Advanced CCD Imaging Spectrometer
Advanced CCD Imaging Spectrometer
ACIS, the AXAF CCD Imaging Spectrometer, is an instrument built by a team from the Massachusetts Institute of Technology's Center for Space Research and the Pennsylvania State University for the Chandra X-ray Observatory...

 (ACIS) and the High Resolution Camera (HRC), moving whichever is called for into position during an observation.

ACIS consists of 10 CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...

 chips and provides images as well as spectral
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...

 information of the object observed. It operates in the range of 0.2 - 10 keV
Kev can refer to:*Kev Hawkins, a fictional character.*Kevin, a given name occasionally shortened to "Kev".*Kiloelectronvolt, a unit of energy who symbol is "KeV".* Krefelder Eislauf-VereinKEV can refer to:...

. HRC has two micro-channel plate components and images over the range of 0.1 - 10 keV. It also has a time resolution of 16 microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...

s. Both of these instruments can be used on their own or in conjunction with one of the observatory's two transmission gratings
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...


The transmission gratings, which swing into the optical path behind the mirrors, provide Chandra with high resolution spectroscopy. The High Energy Transmission Grating Spectrometer (HETGS) works over 0.4 - 10 keV and has a spectral resolution of 60-1000. The Low Energy Transmission Grating Spectrometer (LETGS) has a range of 0.09 - 3 keV and a resolution of 40-2000.

External links

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