NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

's series of Great Observatories

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

s are four large, powerful space-based astronomical telescopes launched between 1990 and 2003. They were built with different technology to examine specific wavelength/energy regions of the

electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...

gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s, visible and

ultraviolet light Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of th ...

, and

infrared light Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those o ...

. The

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

(HST) primarily observes

visible light Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres (nm ...

and near-ultraviolet. It was launched in 1990 aboard the Space Shuttle ''Discovery'' during

STS-31 STS-31 was the 35th mission of NASA's Space Shuttle program and the tenth flight of the Space Shuttle ''Discovery''. The primary purpose of this mission was the deployment of the Hubble Space Telescope (HST) into low Earth orbit. ''Discovery ...

, but its main mirror had been ground incorrectly, resulting in

spherical aberration In optics, spherical aberration (SA) is a type of aberration found in optical systems that have elements with spherical surfaces. This phenomenon commonly affects lenses and curved mirrors, as these components are often shaped in a spherical ...

that compromised the telescope's capabilities. The optics were corrected to their intended quality by the

STS-61 STS-61 was NASA's first Hubble Space Telescope servicing mission, and the fifth flight of the Space Shuttle Endeavour, Space Shuttle ''Endeavour''. The mission launched on December 2, 1993, from Kennedy Space Center (KSC) in Florida. The missi ...

servicing mission in 1993. In 1997, the

STS-82 STS-82 was the 22nd flight of the Space Shuttle Space Shuttle Discovery, ''Discovery'' and the 82nd mission of the Space Shuttle program. It was NASA's second mission to service the Hubble Space Telescope, during which ''Discovery's'' crew repai ...

servicing mission added capability in the

near-infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

range, and in 2009 the

STS-125 STS-125, or HST-SM4 (Hubble Space Telescope Servicing Mission 4), was the fifth and final Space Shuttle mission to the Hubble Space Telescope (HST). The launch of the Space Shuttle ''Atlantis'' occurred on May 11, 2009, at 2:01 pm EDT. Land ...

servicing mission refurbished the telescope and extended its projected service life. It remains in active operation . The

Compton Gamma Ray Observatory The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with photon energy, energies from 20 kElectronvolt#Properties, eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main tel ...

(CGRO) primarily observed

s, though it extended into

hard x-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s as well. It was launched in 1991 aboard ''

Atlantis Atlantis () is a fictional island mentioned in Plato's works '' Timaeus'' and ''Critias'' as part of an allegory on the hubris of nations. In the story, Atlantis is described as a naval empire that ruled all Western parts of the known world ...

'' during

STS-37 STS-37, the thirty-ninth NASA Space Shuttle mission and the eighth flight of the Space Shuttle ''Atlantis'', was a six-day mission with the primary objective of launching the Compton Gamma Ray Observatory (CGRO), the second of the Great Observ ...

. It was de-orbited in 2000 after a gyroscope failed. The

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

(CXO) primarily observes

soft X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s. It was launched in 1999 aboard '' Columbia'' during

STS-93 STS-93 in 1999 marked the 95th launch of the Space Shuttle, the 26th launch of Space Shuttle Columbia, ''Columbia'', and the 21st night launch of a Space Shuttle. Eileen Collins became the first female shuttle Commander on this flight. Its prima ...

into an elliptical high-Earth orbit, and was initially named the Advanced X-ray Astronomical Facility (AXAF). It remains in active operation . The

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicate ...

(SST) observed the

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

spectrum. It was launched in 2003 aboard a Delta II rocket into an Earth-trailing solar orbit. Depletion of its

liquid helium Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temp ...

coolant in 2009 reduced its functionality, leaving it with only two short-wavelength imaging modules. It was removed from service and placed into safe-mode on January 30, 2020.

Origins of the Great Observatory program

The concept of a Great Observatory program was first proposed in the 1979 NRC report "A Strategy for Space Astronomy and Astrophysics for the 1980s". This report laid the essential groundwork for the Great Observatories and was chaired by Peter Meyer (through June 1977) and then by Harlan J. Smith (through publication). In the mid-1980s, it was further advanced by all of the astrophysics Division Directors at

NASA headquarters The Mary W. Jackson NASA Headquarters building at 300 E Street SW in Washington, D.C. houses NASA leadership who provide overall guidance and direction to the US government executive branch agency NASA, under the leadership of the NASA administ ...

, including Frank Martin and Charlie Pellerin. NASA's "Great Observatories" program used four separate satellites, each designed to cover a different part of the spectrum in ways which terrestrial systems could not. This perspective enabled the proposed X-ray and InfraRed observatories to be appropriately seen as a continuation of the astronomical program begun with Hubble and CGRO rather than competitors or replacements. Two explanatory documents published by NASA and created for the NASA Astrophysics Division and the NASA Astrophysics Management Working Group laid out the rationale for the suite of observatories and questions that could be addressed across the spectrum. They had an important role in the campaign to win and sustain approval for the four telescopes.

Great Observatories

Hubble Space Telescope

The history of the Hubble Space Telescope can be traced back to 1946, when the

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

Lyman Spitzer Lyman Spitzer Jr. (June 26, 1914 – March 31, 1997) was an American theoretical physicist, astronomer and mountaineer. As a scientist, he carried out research into star formation and plasma physics and in 1946 conceived the idea of telesco ...

wrote the paper ''Astronomical advantages of an extraterrestrial observatory''. Spitzer devoted much of his career to pushing for a space telescope. The 1966–1972 Orbiting Astronomical Observatory missions demonstrated the important role space-based observations could play in astronomy. In 1968, NASA developed firm plans for a space-based

reflecting telescope A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...

with a 3-meter mirror, known provisionally as the Large Orbiting Telescope or Large Space Telescope (LST), with a launch slated for 1979. Congress eventually approved funding of US$36 million for 1978, and the design of the LST began in earnest, aiming for a launch date of 1983. During the early 1980s, the telescope was named after

Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology. Hubble proved that many objects previously ...

. Hubble was originally intended to be retrieved and returned to

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

by the

Space Shuttle The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...

, but the retrieval plan was later abandoned. On 31 October 2006,

NASA Administrator The administrator of the National Aeronautics and Space Administration is the highest-ranking official of NASA, the national List of space agencies, space agency of the United States. The administrator is NASA's chief decision maker, responsible ...

Michael D. Griffin gave the go-ahead for a final refurbishment mission. The 11-day

mission by Space Shuttle ''Atlantis'', launched on 11 May 2009, installed fresh batteries, replaced all gyroscopes, replaced a command computer, fixed several instruments, and installed the

Wide Field Camera 3 The Wide Field Camera 3 (WFC3) is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum. It was installed as a replacement for the Wide Field and Planetary Camera 2 during the first ...

and the Cosmic Origins Spectrograph.

Compton Gamma Ray Observatory

Gamma rays had been examined above the atmosphere by several early space missions. During its High Energy Astronomy Observatory Program in 1977, NASA announced plans to build a "great observatory" for

gamma-ray astronomy Gamma-ray astronomy is a subfield of astronomy where scientists observe and study celestial objects and phenomena in outer space which emit cosmic electromagnetic radiation in the form of gamma rays,Astronomical literature generally hyphena ...

. The Gamma Ray Observatory (GRO), renamed

Compton Gamma-Ray Observatory The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with energies from 20 k eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main telescopes in one spacecraft, covering X- ...

(CGRO), was designed to take advantage of the major advances in detector technology during the 1980s. Following 14 years of effort, the CGRO was launched on 5 April 1991. One of the three

gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining Orientation (geometry), orientation and angular velocity. It is a spinning wheel or disc in ...

s on the Compton Gamma Ray Observatory failed in December 1999. Although the observatory was fully functional with two gyroscopes, NASA judged that failure of a second gyroscope would result in inability to control the satellite during its eventual return to Earth due to orbital decay. NASA chose instead to preemptively de-orbit Compton on 4 June 2000. Parts that survived reentry splashed into the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

Chandra X-ray Observatory

In 1976 the

(called AXAF at the time) was proposed to NASA by

Riccardo Giacconi Riccardo Giacconi ( , ; October 6, 1931 – December 9, 2018) was an Italian-American Nobel Prize-winning astrophysicist who laid down the foundations of X-ray astronomy. He was a professor at the Johns Hopkins University. Biography Born in ...

and Harvey Tananbaum. Preliminary work began the following year at

Marshall Space Flight Center Marshall Space Flight Center (officially the George C. Marshall Space Flight Center; MSFC), located in Redstone Arsenal, Alabama (Huntsville, Alabama, Huntsville postal address), is the Federal government of the United States, U.S. government's ...

(MSFC) and the

Smithsonian Astrophysical Observatory The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution, concentrating on Astrophysics, astrophysical studies including Galactic astronomy, galactic and extragalactic astronomy, cosmology, Sun, solar ...

(SAO). In the meantime, in 1978, NASA launched the first imaging X-ray telescope,

Einstein Observatory Einstein Observatory (HEAO-2) was the first fully imaging X-ray telescope put into space and the second of NASA's three HEAO Program, High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to ho ...

(HEAO-2), into orbit. Work continued on the Chandra project through the 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

but put the observatory above the Earth's radiation belts for most of its orbit.

Spitzer Space Telescope

By the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of

atmosphere of Earth The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weather ...

. Most of the early concepts, envisioned repeated flights aboard the NASA Space Shuttle. This approach was developed in an era when the Shuttle program was presumed to be capable of supporting weekly flights of up to 30 days duration. In 1979, a National Research Council of the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, NGO, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the ...

report, ''A Strategy for Space Astronomy and Astrophysics for the 1980s'', identified a ''Shuttle Infrared Telescope Facility'' (SIRTF) as "one of two major astrophysics facilities o be developedfor

Spacelab Spacelab was a reusable laboratory developed by European Space Agency (ESA) and used on certain spaceflights flown by the Space Shuttle. The laboratory comprised multiple components, including a pressurized module, an unpressurized carrier, ...

," a Shuttle-borne platform. The launch of the

Infrared Astronomical Satellite The Infrared Astronomical Satellite ( Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mo ...

, an Explorer-class satellite designed to conduct the first

survey of the sky led to anticipation of an instrument using new infrared detector technology. By September 1983, NASA was considering the "possibility of a long duration ree-flyerSIRTF mission". The 1985 Spacelab-2 flight aboard

STS-51-F STS-51-F (also known as Spacelab 2) was the 19th flight of NASA's Space Shuttle program and the eighth flight of Space Shuttle ''Challenger''. It launched from Kennedy Space Center, Florida, on July 29, 1985, and landed eight days later on Au ...

confirmed the Shuttle environment was not well suited to an onboard infrared telescope, and a free-flying design was better. The first word of the name was changed from ''Shuttle'' so it would be called the Space Infrared Telescope Facility. Spitzer was the only one of the Great Observatories not launched by the Space Shuttle. It was originally intended to be so launched, but after the ''Challenger'' disaster, the

Centaur A centaur ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...

LH2 Liquid hydrogen () is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid stat ...

/ LOX

upper stage A multistage rocket or step rocket is a launch vehicle that uses two or more rocket ''stages'', each of which contains its own Rocket engine, engines and Rocket propellant, propellant. A ''tandem'' or ''serial'' stage is mounted on top of anoth ...

that would have been required to push it into a

heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun ...

was banned from Shuttle use.

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

and

Atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

launch vehicles were canceled for cost reasons. After redesign and lightening, it was launched in 2003 by a

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...

launch vehicle A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...

instead. It was called the Space Infrared Telescope Facility (SIRTF) before launch. The telescope was deactivated when operations ended on 30 January 2020.

Timeline

Strengths

Since the Earth's atmosphere prevents

X-rays An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

gamma-rays A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

and

far-infrared Far infrared (FIR) or long wave refers to a specific range within the infrared spectrum of electromagnetic radiation. It encompasses radiation with wavelengths ranging from 15 μm ( micrometers) to 1 mm, which corresponds to a freque ...

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

from reaching the ground, space missions were essential for the Compton, Chandra and Spitzer observatories. Hubble also benefits from being above the atmosphere, as the atmosphere blurs ground-based observations of very faint objects, decreasing spatial resolution (however brighter objects can be imaged in much higher resolution than by Hubble from the ground using

astronomical interferometer An astronomical interferometer or telescope array is a set of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope to provide higher resolution images of astronomical objects such as stars, n ...

s or

adaptive optics Adaptive optics (AO) is a technique of precisely deforming a mirror in order to compensate for light distortion. It is used in Astronomy, astronomical telescopes and laser communication systems to remove the effects of Astronomical seeing, atmo ...

). Larger, ground-based telescopes have only recently matched Hubble in resolution for near-infrared wavelengths of faint objects. Being above the atmosphere eliminates the problem of

airglow Airglow is a faint emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky never to be completely dark, even after the effects of starlight and diffuse sky radiation, diffuse ...

, allowing Hubble to make observations of ultrafaint objects. Ground-based telescopes cannot compensate for airglow on ultrafaint objects, and so very faint objects require unwieldy and inefficient exposure times. Hubble can also observe at

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

wavelengths which do not penetrate the atmosphere. Each observatory was designed to push the state of technology in its region of the electromagnetic spectrum. Compton was much larger than any gamma-ray instruments flown on the previous HEAO missions, opening entirely new areas of observation. It had four instruments covering the 20

keV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...

to 30 GeV energy range, which complemented each other's sensitivities, resolutions, and fields of view. Gamma rays are emitted by various high-energy and high-temperature sources, such as

black hole A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...

pulsar A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...

s, and

supernovae A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original ob ...

. Chandra similarly had no ground predecessors. It followed the three NASA HEAO Program satellites, notably the highly successful

, which was the first to demonstrate the power of grazing-incidence, focusing X-ray optics, giving spatial resolution an order of magnitude better than

collimated A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A laser beam is an archetypical example. A perfectly collimated light beam, with no divergence, would not disp ...

instruments (comparable to optical telescopes), with an enormous improvement in sensitivity. Chandra's large size, high orbit, and sensitive CCDs allowed observations of very faint X-ray sources. Spitzer also observes at wavelength largely inaccessible to ground telescopes. It was preceded in space by NASA's smaller

IRAS The Infrared Astronomical Satellite (Dutch language, Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a astronomical survey, survey of the entire night sky at infrared wavelengths. Launched on 25 Janu ...

mission and

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

(ESA)'s large

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

telescope. Spitzer's instruments took advantage of the rapid advances in infrared detector technology since IRAS, combined with its large aperture, favorable fields of view, and long life. Science returns were accordingly outstanding. Infrared observations are necessary for very distant astronomical objects where all the visible light is

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...

ed to infrared wavelengths, for cool objects which emit little visible light, and for regions optically obscured by dust.

Synergies

Aside from inherent mission capabilities (particularly sensitivities, which cannot be replicated by ground observatories), the Great Observatories program allows missions to interact for greater science return. Different objects shine in different wavelengths, but training two or more observatories on an object allows a deeper understanding. High-energy studies (in X-rays and gamma rays) have had only moderate imaging resolutions so far. Studying X-ray and gamma-ray objects with Hubble, as well as Chandra and Compton, gives accurate size and positional data. In particular, Hubble's resolution can often discern whether the target is a standalone object, or part of a parent galaxy, and if a bright object is in the nucleus, arms, or halo of a

spiral galaxy Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''

List of the most distant astronomical objects This article documents the most distant Astronomical object, astronomical objects discovered and verified so far, and the time periods in which they were so classified. For comparisons with the light travel distance of the astronomical objects li ...

) Ultraviolet studies with Hubble also reveal the temporal states of high-energy objects. X-rays and gamma rays are harder to detect with current technologies than visible and ultraviolet. Therefore, Chandra and Compton needed long integration times to gather enough photons. However, objects which shine in X-rays and gamma rays can be small, and can vary on timescales of minutes or seconds. Such objects then call for followup with Hubble or the Rossi X-ray Timing Explorer, which can measure details in angular seconds or fractions of a second, due to different designs. Rossi's last full year of operation was 2011. The ability of Spitzer to see through dust and thick gases is good for galactic nuclei observations. Massive objects at the hearts of galaxies shine in X-rays, gamma rays, and radio waves, but infrared studies into these clouded regions can reveal the number and positions of objects. Hubble, meanwhile, has neither the

field of view The field of view (FOV) is the angle, angular extent of the observable world that is visual perception, seen at any given moment. In the case of optical instruments or sensors, it is a solid angle through which a detector is sensitive to elec ...

nor the available time to study all interesting objects. Worthwhile targets are often found with ground telescopes, which are cheaper, or with smaller space observatories, which are sometimes expressly designed to cover large areas of the sky. Also, the other three Great Observatories have found interesting new objects, which merit diversion of Hubble. One example of observatory synergy is

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

and

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

studies. Small bodies, such as small

moons A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are colloquially referred to as moons, a deriva ...

and asteroids, are too small and/or distant to be directly resolved even by Hubble; their image appears as a

diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...

pattern determined by brightness, not size. However, the minimum size can be deduced by Hubble through knowledge of the body's

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

. The maximum size can be determined by Spitzer through knowledge of the body's temperature, which is largely known from its orbit. Thus, the body's true size is bracketed. Further

spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

by Spitzer can determine the chemical composition of the object's surface, which limits its possible albedos, and therefore sharpens the low size estimate. At the opposite end of the

cosmic distance ladder The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...

, observations made with Hubble, Spitzer and Chandra have been combined in the Great Observatories Origins Deep Survey to yield a multi-wavelength picture of

galaxy formation and evolution In cosmology, the study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the process ...

in the early

Universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

Impact

All four telescopes have had a substantial impact on astronomy. The opening up of new wavebands to high resolution, high sensitivity observations by the Compton, Chandra and Spitzer has revolutionized our understanding of a wide range of astronomical objects, and has led to the detection of thousands of new, interesting objects. Hubble has had a much larger public and media impact than the other telescopes, although at optical wavelengths Hubble has provided a more modest improvement in sensitivity and resolution over existing instruments. Hubble's capability for uniform high-quality imaging of any astronomical object at any time has allowed accurate surveys and comparisons of large numbers of astronomical objects. The

Hubble Deep Field The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area about 2.6 arcminutes on a side, about one 24-millionth of the ...

observations have been very important for studies of distant galaxies, as they provide rest-frame ultraviolet images of these objects with a similar number of pixels across the galaxies as previous ultraviolet images of closer galaxies, allowing direct comparison.

Successors to Great Observatories

* The

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...

(JWST) launched in December 2021 and works simultaneously with Hubble. Its segmented, deployable mirror is over twice as wide as the Hubble's, increasing angular resolution noticeably, and sensitivity dramatically. Unlike Hubble, JWST observes in the infrared, in order to penetrate dust at cosmological distances. This means it continues some Spitzer capabilities, while some Hubble capabilities are lost in the visible and especially the ultraviolet wavelengths. JWST exceeds Spitzer's performance in near-infrared. The European Space Agency's

Herschel Space Observatory The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telesco ...

, operational from 2009 to 2013, has exceeded Spitzer in the far-infrared. The SOFIA (

Stratospheric Observatory for Infrared Astronomy The Stratospheric Observatory For Infrared Astronomy (SOFIA) was an 80/20 joint project of NASA and the German Aerospace Center (DLR) to construct and maintain an airborne observatory. NASA awarded the contract for the development of the aircra ...

) airborne platform observed in near- and mid-infrared. SOFIA had a larger aperture than Spitzer, but lower relative sensitivity. * The

Fermi Gamma-ray Space Telescope The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is ...

(FGRST), formerly known as the Gamma Ray Large Area Space Telescope, is a follow-on to Compton launched on 11 June 2008. FGRST is more narrowly defined, and much smaller; it carries only one main instrument and a secondary experiment, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). FGRST is complemented by

Swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIF ...

, launched in 2004, and previously by HETE-2, launched in 2000. * The

Reuven Ramaty High Energy Solar Spectroscopic Imager Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI, originally High Energy Solar Spectroscopic Imager or HESSI or Explorer 81) was a NASA solar flare observatory. It was the sixth mission in the Small Explorer program (SMEX), selecte ...

(RHESSI), observed in some Compton and Chandra wavelengths between its February 2002 launch and April 2023 decommissioning. RHESSI was pointed at the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

at all times, but it occasionally observed high-energy objects in its peripheral view. * Another large, high-energy observatory is

INTEGRAL In mathematics, an integral is the continuous analog of a Summation, sum, which is used to calculate area, areas, volume, volumes, and their generalizations. Integration, the process of computing an integral, is one of the two fundamental oper ...

, Europe's INTErnational Gamma Ray Astrophysics Laboratory, launched in 2002. It observes in similar frequencies to Compton. INTEGRAL uses a fundamentally different telescope technology, coded-aperture masks. Thus, its capabilities are complementary to Compton and Fermi.

Later programs

* The Beyond Einstein program will seek to develop new areas of science. Constellation-X and the

Laser Interferometer Space Antenna The Laser Interferometer Space Antenna (LISA) is a planned space probe to detect and measure gravitational waves—tiny ripples in the fabric of spacetime—from astronomical sources. LISA will be the first dedicated space-based gravitational-w ...

(LISA) have been referred to by NASA as the Einstein Great Observatories, to differentiate them from the current generation. However, they are not a part of the Great Observatories program. * The International Solar-Terrestrial Physics Science Initiative (ISTP), in the spirit of the Great Observatories program, is a group of instruments to study the Sun and related electromagnetic phenomena near Earth.

Next Great Observatory

In 2016,

began considering four different

Flagship A flagship is a vessel used by the commanding officer of a group of navy, naval ships, characteristically a flag officer entitled by custom to fly a distinguishing flag. Used more loosely, it is the lead ship in a fleet of vessels, typically ...

space telescope A space telescope (also known as space observatory) is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO ...

s, they are the Habitable Exoplanet Imaging Mission (HabEx), Large UV Optical Infrared Surveyor (LUVOIR), Origins Space Telescope (OST), and Lynx X-ray Observatory. In 2019, the four teams will turn their final reports over to the

, whose independent Decadal Survey committee advises NASA on which mission should take top priority.

announced the

Habitable Worlds Observatory The Habitable Worlds Observatory (HWO) is a proposed next generation space telescope, a successor of the flagship Hubble, Webb and Roman projects. It would have a large 6–8 meter mirror and be able to detect infrared, optical, and ultraviolet ...

(HWO) in 2023, a successor building on the Large UV Optical Infrared Surveyor (LUVOIR) and Habitable Exoplanet Imaging Mission (HabEX) proposals. The administration also created the Great Observatory Maturation Program for the development of the

Notes and references

External links

*
STS-125: Final Shuttle Mission to Hubble Space Telescope

Great Observatories Interactive using WorldWide Telescope
{{Hubble Space Telescope Space telescopes NASA programs Spitzer Space Telescope Hubble Space Telescope Chandra X-ray Observatory Gamma-ray telescopes