Editing Infrared astronomy

{{Short description|Observation of infrared wavelengths}}
{{morefootnotes|date=November 2022}}
{{Use dmy dates|date=April 2019}}
'''Infrared astronomy''' is a sub-discipline of [[astronomy]] which specializes in the [[astronomical observation|observation]] and analysis of [[astronomical object]]s using [[infrared]] (IR) radiation. The [[wavelength]] of infrared light ranges from 0.75 to 300 micrometers, and falls in between [[Visible light|visible]] radiation, which ranges from 380 to 750 [[nanometer]]s, and [[terahertz radiation|submillimeter]] waves.

Infrared astronomy began in the 1830s,{{Citation needed|date=July 2024}} a few decades after the discovery of infrared light by [[William Herschel]] in 1800.<ref name="caltech_herschel" /> Early progress was limited, and it was not until the early 20th century that conclusive detections of astronomical objects other than the [[Sun]] and [[Moon]] were made in infrared light.{{Citation needed|date=July 2024}} After a number of discoveries were made in the 1950s and 1960s in [[radio astronomy]], astronomers realized the information available outside the visible wavelength range, and modern infrared astronomy was established.<ref name="rieke" />

Infrared and [[optical astronomy]] are often practiced using the same [[telescope]]s, as the same [[mirror]]s or [[lens (optics)|lens]]es are usually effective over a wavelength range that includes both visible and infrared light. Both fields also use [[Solid state (electronics)|solid state]] detectors, though the specific type of solid state [[photodetector]]s used are different. Infrared light is [[absorption (electromagnetic radiation)|absorb]]ed at many wavelengths by [[water vapor]] in the [[Earth's atmosphere]], so most infrared telescopes are at high elevations in dry places, above as much of the atmosphere as possible. There have also been infrared observatories [[Space telescope|in space]], including the [[Spitzer Space Telescope]], the [[Herschel Space Observatory]], and more recently the [[James Webb Space Telescope]].<ref name=":0" />

==History==
[[File:NICMOS cross cut.png|thumb|Hubble's ground-breaking near-infrared NICMOS]]
[[File:SOFIA with open telescope doors.jpg|thumb|right|200px|[[SOFIA]] is an infrared telescope in an aircraft, shown here in a 2009 test]]
The discovery of infrared radiation is attributed to William Herschel, who performed an experiment in 1800 where he placed a thermometer in sunlight of different colors after it passed through a [[prism (optics)|prism]].<ref name="caltech_herschel" /> He noticed that the temperature increase induced by sunlight was highest ''outside'' the visible spectrum, just beyond the red color. That the temperature increase was highest at infrared wavelengths was due to the spectral response of the prism rather than properties of the Sun, but the fact that there was any temperature increase at all prompted Herschel to deduce that there was invisible radiation from the Sun. He dubbed this radiation "calorific rays", and went on to show that it could be reflected, transmitted, and absorbed just like visible light.<ref name="caltech_herschel">{{cite web|url=http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_bio.html |title=Herschel Discovers Infrared Light |access-date=9 April 2010 |publisher=Cool Cosmos |url-status=dead |archive-url=https://web.archive.org/web/20120225094516/http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_bio.html |archive-date=25 February 2012  }}</ref>

[[File:Wrapped Up for the Cool Cosmos.jpg|thumb|left|High on the Chajnantor Plateau, the [[Atacama Large Millimeter Array]] provides an extraordinary place for infrared astronomy.<ref>{{cite news|title=First Results from the ESO Ultra HD Expedition|url=http://www.eso.org/public/announcements/ann14035/|access-date=10 May 2014|newspaper=ESO Announcement}}</ref>]]

Efforts were made starting in the 1830s and continuing through the 19th century to detect infrared radiation from other astronomical sources. Radiation from the Moon was first detected in 1856 by [[Charles Piazzi Smyth]], the Astronomer Royal for Scotland, during an expedition to Tenerife to test his ideas about mountain top astronomy. [[Ernest Fox Nichols]] used a modified [[Crookes radiometer]] in an attempt to detect infrared radiation from [[Arcturus]] and [[Vega]], but Nichols deemed the results inconclusive. Even so, the ratio of flux he reported for the two [[star]]s is consistent with the modern value, so [[George Rieke]] gives Nichols credit for the first detection of a star other than our own in the infrared.<ref name="rieke">{{cite journal | author = Rieke, George H. | title = History of infrared telescopes and astronomy | journal = Experimental Astronomy | volume = 25 | issue = 1–3 | pages = 125–141 | date = 2009 | doi = 10.1007/s10686-009-9148-7 | bibcode = 2009ExA....25..125R| s2cid = 121996857 }}</ref>

The field of infrared astronomy continued to develop slowly in the early 20th century, as [[Seth Barnes Nicholson]] and [[Edison Pettit]] developed [[thermopile]] detectors capable of accurate infrared [[photometry (astronomy)|photometry]] and sensitive to a few hundreds of stars. The field was mostly neglected by traditional astronomers until the 1960s, with most scientists who practiced infrared astronomy having actually been trained [[physicist]]s. The success of radio astronomy during the 1950s and 1960s, combined with the improvement of [[infrared detector]] technology, prompted more astronomers to take notice, and infrared astronomy became well established as a subfield of astronomy.<ref name="rieke"/><ref>{{cite book |last=Glass |first=Ian S. |date=1999 |title=Handbook of Infrared Astronomy |publisher=[[Cambridge University Press]]|location=Cambridge, England |isbn=0-521-63311-7}}</ref>

Infrared [[space telescope]]s entered service. [[United States Air Force Infrared Sky Surveys|Early infrared sky surveys]] were carried out by the United States Air Force using [[sounding rocket]]s.<ref name="Price2008"/> In 1983, [[IRAS]] made an all-sky survey. In 1995, the European Space Agency created the [[Infrared Space Observatory]]. Before this satellite ran out of [[liquid helium]] in 1998, it discovered protostars and water in our universe (even on Saturn and Uranus).<ref>{{Cite web|url=http://link.galegroup.com/apps/doc/CV2644300557/SCIC?u=mcc_pv&xid=d1c570e6|title=Science in Context - Document|website=link.galegroup.com|language=en|access-date=25 September 2017}}</ref>

On 25 August 2003, NASA launched the [[Spitzer Space Telescope]], previously known as the Space Infrared Telescope Facility.  In 2009, the telescope ran out of liquid helium and lost the ability to see [[far infrared]].  It had discovered stars, the [[Double Helix Nebula]], and light from [[extrasolar planet]]s.  It continued working in 3.6 and 4.5 micrometer bands.  Since then, other infrared telescopes helped find new stars that are forming, nebulae, and stellar nurseries. Infrared telescopes have opened up a whole new part of the galaxy for us. They are also useful for observing extremely distant things, like [[quasar]]s. Quasars move away from Earth. The resulting large redshift make them difficult targets with an optical telescope. Infrared telescopes give much more information about them.

During May 2008, a group of international infrared astronomers proved that [[intergalactic dust]] greatly dims the light of distant galaxies. In actuality, galaxies are almost twice as bright as they look. The dust absorbs much of the visible light and re-emits it as infrared light.

== Modern infrared astronomy ==
[[File:New Hubble infrared view of the Tarantula Nebula.jpg|thumb|[[Hubble Space Telescope|Hubble]] infrared view of the [[Tarantula Nebula]].<ref>{{cite news|title=Unravelling the web of a cosmic creeply-crawly|url=http://www.spacetelescope.org/news/heic1402/|access-date=18 January 2014|newspaper=ESA/Hubble Press Release}}</ref> ]]

Infrared radiation with wavelengths just longer than visible light, known as near-infrared, behaves in a very similar way to visible light, and can be detected using similar solid state devices (because of this, many quasars, stars, and galaxies were discovered). For this reason, the near infrared region of the spectrum is commonly incorporated as part of the "optical" spectrum, along with the near ultraviolet. Many [[optical telescope]]s, such as those at [[Keck Observatory]], operate effectively in the near infrared as well as at visible wavelengths. The far-infrared extends to [[Submillimetre astronomy|submillimeter wavelengths]], which are observed by telescopes such as the [[James Clerk Maxwell Telescope]] at [[Mauna Kea Observatory]].

[[File:Artist's impression of the galaxy W2246-0526.jpg|left|thumb|Artist impression of galaxy [[W2246-0526]], a single galaxy glowing in infrared light as intensely as 350 trillion Suns.<ref>{{cite web|title=Artist's impression of the galaxy W2246-0526|url=https://www.eso.org/public/images/eso1602a/ |work=ESO.org|access-date=18 January 2016}}</ref>]]

Like all other forms of [[electromagnetic radiation]], infrared is utilized by astronomers to study the [[universe]]. Indeed, infrared measurements taken by the [[2MASS]] and [[Wide-field Infrared Survey Explorer|WISE]] astronomical surveys have been particularly effective at unveiling previously undiscovered [[star clusters]].<ref name=fr2007>{{Cite journal|bibcode = 2007MNRAS.374..399F|title = A systematic survey for infrared star clusters with &#124;b&#124; <20° using 2MASS|last1 = Froebrich|first1 = D.|last2 = Scholz|first2 = A.|last3 = Raftery|first3 = C. L.|journal = Monthly Notices of the Royal Astronomical Society|year = 2007|volume = 374|issue = 2|page = 399|doi = 10.1111/j.1365-2966.2006.11148.x| doi-access=free |arxiv = astro-ph/0610146|s2cid = 15339002}}</ref><ref name=ma2013>{{Cite journal|url=http://adsabs.harvard.edu/abs/2013Ap%26SS.344..175M|bibcode=2013Ap&SS.344..175M|title=Discovering protostars and their host clusters via WISE|last1=Majaess|first1=D.|journal=Astrophysics and Space Science|year=2013|volume=344|issue=1|page=175|doi=10.1007/s10509-012-1308-y|arxiv=1211.4032|s2cid=118455708}}</ref> Examples of such embedded star clusters are FSR 1424, FSR 1432, Camargo 394, Camargo 399, Majaess 30, and Majaess 99.<ref name=ca2015a>{{Cite journal|url=http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1406.3099|bibcode = 2015NewA...34...84C|title = New Galactic embedded clusters and candidates from a WISE Survey|last1 = Camargo|first1 = Denilso|last2 = Bica|first2 = Eduardo|last3 = Bonatto|first3 = Charles|journal = New Astronomy|year = 2015|volume = 34|pages = 84–97|doi = 10.1016/j.newast.2014.05.007|arxiv = 1406.3099|s2cid = 119002533}}</ref><ref>{{Cite journal |doi=10.1093/mnras/stt703|title=Towards a census of the Galactic anticentre star clusters – III. Tracing the spiral structure in the outer disc|year=2013|last1=Camargo|first1=D.|last2=Bica|first2=E.|last3=Bonatto|first3=C.|journal=Monthly Notices of the Royal Astronomical Society|volume=432|issue=4|pages=3349–3360|doi-access=free|hdl=10183/93387|hdl-access=free}}</ref><ref name=ca2015b>{{Cite journal|url=http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1505.01829|bibcode=2015MNRAS.450.4150C|title=Tracing the Galactic spiral structure with embedded clusters|last1=Camargo|first1=D.|last2=Bonatto|first2=C.|last3=Bica|first3=E.|journal=Monthly Notices of the Royal Astronomical Society|year=2015|volume=450|issue=4|pages=4150–4160|doi=10.1093/mnras/stv840|doi-access=free |arxiv=1505.01829}}</ref> Infrared telescopes, which includes most major optical telescopes as well as a few dedicated infrared telescopes, need to be chilled with [[liquid nitrogen]] and shielded from warm objects. The reason for this is that objects with temperatures of a few hundred [[kelvin]]s emit most of their [[thermal energy]] at infrared wavelengths. If infrared detectors were not kept cooled, the radiation from the detector itself would contribute noise that would dwarf the radiation from any celestial source. This is particularly important in the mid-infrared and far-infrared regions of the spectrum.

To achieve higher [[angular resolution]], some infrared telescopes are combined to form [[astronomical interferometer]]s. The effective resolution of an interferometer is set by the distance between the telescopes, rather than the size of the individual telescopes. When used together with [[adaptive optics]], infrared interferometers, such as two 10 meter telescopes at Keck Observatory or the four 8.2 meter telescopes that make up the [[Very Large Telescope]] Interferometer, can achieve high angular resolution.

[[File:Atmosfaerisk spredning.png|thumb|upright=2.0|Atmospheric windows in the infrared.]]
The principal limitation on infrared sensitivity from ground-based telescopes is the Earth's atmosphere. Water vapor absorbs a significant amount of infrared radiation, and the atmosphere itself emits at infrared wavelengths. For this reason, most infrared telescopes are built in very dry places at high altitude, so that they are above most of the water vapor in the atmosphere. Suitable locations on Earth include [[Mauna Kea Observatory]] at 4205 meters above sea level, the [[Paranal Observatory]] at 2635 meters in [[Chile]] and regions of high altitude ice-desert such as [[Dome C]] in [[Antarctic]]. Even at high altitudes, the transparency of the Earth's atmosphere is limited except in [[infrared window]]s, or wavelengths where the Earth's atmosphere is transparent.<ref name="caltech_windows">{{cite web | url = http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/irwindows.html | title = IR Atmospheric Windwows | access-date = 9 April 2009 | publisher = Cool Cosmos | archive-date = 11 October 2018 | archive-url = https://web.archive.org/web/20181011101051/http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/irwindows.html | url-status = dead }}</ref> The main infrared windows are listed below:

{| class="wikitable" style="width: 90%; margin: 1em auto 1em auto;"
|- valign="top"
!width=13%|Spectrum
!width=13%|Wavelength<br>([[micrometre]]s)
!width=13%|Astronomical<br>bands
!width=61%|Telescopes
|-
|Near Infrared
|0.65 to 1.0
|R and I bands
|All major optical telescopes
|-
|Near Infrared
|1.1 to 1.4
|[[J band (infrared)|J band]]
|Most major optical telescopes and most dedicated infrared telescopes
|-
|Near Infrared
|1.5 to 1.8
|[[H band (infrared)|H band]]
|Most major optical telescopes and most dedicated infrared telescopes
|-
|Near Infrared
|2.0 to 2.4
||[[K band (infrared)|K band]]
|Most major optical telescopes and most dedicated infrared telescopes
|-
|Near Infrared
|3.0 to 4.0
|[[L band (infrared)|L band]]
|Most dedicated infrared telescopes and some optical telescopes
|-
|Near Infrared
|4.6 to 5.0
||[[M band (infrared)|M band]]
|Most dedicated infrared telescopes and some optical telescopes
|-
|Mid Infrared
|7.5 to 14.5
|[[N band]]
|Most dedicated infrared telescopes and some optical telescopes
|-
|Mid Infrared
|17 to 25
|Q band
|Some dedicated infrared telescopes and some optical telescopes
|-
|Far Infrared
|28 to 40
|Z band
|Some dedicated infrared telescopes and some optical telescopes
|-
|Far Infrared
|330 to 370
|
|Some dedicated infrared telescopes and some optical telescopes
|-
|Far Infrared
|450
|[[Submillimetre astronomy|submillimeter]]
|Submillimeter telescopes
|}

As is the case for visible light telescopes, space is the ideal place for infrared telescopes. Telescopes in space can achieve higher resolution, as they do not suffer from [[scintillation (astronomy)|blurring]] caused by the Earth's atmosphere, and are also free from infrared absorption caused by the Earth's atmosphere. Current infrared telescopes in space include the [[Herschel Space Observatory]], the [[Spitzer Space Telescope]], the [[Wide-field Infrared Survey Explorer]] and the [[James Webb Space Telescope]]. Since putting telescopes in orbit is expensive, there are also [[Airborne observatory|airborne observatories]], such as the [[Stratospheric Observatory for Infrared Astronomy]] and the [[Kuiper Airborne Observatory]]. These observatories fly above most, but not all, of the atmosphere, and water vapor in the atmosphere absorbs some of infrared light from space. 
{{Multiple image|direction=horizontal|align=center|width=300|image1=15-044a-SuperNovaRemnant-PlanetFormation-SOFIA-20150319.jpg|image2=15-044b-SuperNovaRemnant-PlanetFormation-SOFIA-20150319.jpg|footer=[[SOFIA]] science — [[supernova remnant]] ejecta producing planet-forming material.}}

== Infrared technology ==
One of the most common infrared detector arrays used at research telescopes is [[HgCdTe]] arrays. These operate well between 0.6 and 5 micrometre wavelengths. For longer wavelength observations or higher sensitivity other detectors may be used, including other [[narrow gap semiconductor]] detectors, low temperature [[bolometer]] arrays or photon-counting [[Superconducting]] Tunnel Junction arrays.

Special requirements for infrared astronomy include: very low dark currents to allow long integration times, associated low noise [[Readout integrated circuit|readout circuits]] and sometimes very high [[pixel]] counts.

Low temperature is often achieved by a coolant, which can run out.<ref name=werner>{{cite web | url = http://www.spacenews.com/civil/101005-last-minute-reprieve.html | archive-url = https://archive.today/20121209065100/http://www.spacenews.com/civil/101005-last-minute-reprieve.html | url-status = dead | archive-date = 9 December 2012 | title = Last-minute Reprieve Extends WISE Mission | publisher = [[Space News]] | date = 5 October 2010 | access-date = 14 January 2014 | first = Debra | last = Werner}}</ref> Space missions have either ended or shifted to "warm" observations when the coolant supply used up.<ref name=werner/> For example, [[Wide-field Infrared Survey Explorer|WISE]] ran out of coolant in October 2010, about ten months after being launched.<ref name=werner/> (See also [[NICMOS]], Spitzer Space Telescope)

== Observatories ==

=== Space observatories ===

Many space telescopes detect electromagnetic radiation in a wavelength range that overlaps at least to some degree with the infrared wavelength range.  Therefore it is difficult to define which space telescopes are infrared telescopes.  Here the definition of "infrared space telescope" is taken to be a space telescope whose main mission is detecting infrared light.

Eight infrared space telescopes have been operated in space. They are:

* [[Infrared Astronomical Satellite]] (IRAS), operated 1983 (10 months). A joint mission of US ([[NASA]]), UK and the Netherlands.
* [[Infrared Space Observatory]] (ISO), operated 1995-1998, [[ESA]] mission.
* [[Midcourse Space Experiment]] (MSX), operated 1996-1997, [[Ballistic Missile Defense Organization|BMDO]] mission.
* [[Spitzer Space Telescope]], operated 2003-2020, [[NASA]] mission.
* [[Akari (satellite)|Akari]], operated 2006-2011, [[JAXA]] mission.
* [[Herschel Space Observatory]], operated 2009-2013, [[ESA]] mission.
* [[Wide-field Infrared Survey Explorer]] (WISE), operated 2009-2024, [[NASA]] mission.
* [[James Webb Space Telescope]] (JWST), operated 2022-, [[NASA]] mission.<ref name=":0">{{Cite news |last=Strickland |first=Ashley |date=11 July 2022 |title=President Biden reveals the James Webb Space Telescope's stunning first image |website=[[CNN]] |url=https://www.cnn.com/2022/07/11/world/james-webb-space-telescope-first-image-scn/index.html |url-status=live |access-date=2022-07-12 |archive-url=https://web.archive.org/web/20220712040743/https://www.cnn.com/2022/07/11/world/james-webb-space-telescope-first-image-scn/index.html |archive-date=2022-07-12}}</ref>
* [[Euclid (spacecraft)|Euclid]] telescope, operated 2023-, [[ESA]] mission.
* [[SPHEREx]] telescope, operated 2025-, NASA mission.<ref name="nasa-20220803">{{cite web |last=Interrante |first=Abbey |url=https://blogs.nasa.gov/punch/2022/08/03/punch-announces-rideshare-with-spherex-and-new-launch-date/ |title=PUNCH Announces Rideshare with SPHEREx and New Launch Date |date=3 August 2022 |access-date=3 August 2022 |work=[[NASA]]}}</ref>

NASA is also planning to launch the [[Nancy Grace Roman Space Telescope]] (NGRST), originally known as the Wide Field InfraRed Space Telescope (WFIRST), in 2027.<ref name="nasa-20220719">{{cite press release |url=https://www.nasa.gov/press-release/nasa-awards-launch-services-contract-for-roman-space-telescope |title=NASA Awards Launch Services Contract for Roman Space Telescope |work=[[NASA]] |date=19 July 2022 |access-date=19 July 2022}}</ref>

Many other smaller space-missions and space-based detectors of infrared radiation have been operated in space. These include the [[STS-51-F|Infrared Telescope]] (IRT) that flew with the [[Space Shuttle]].

The [[Submillimeter Wave Astronomy Satellite]] (SWAS) is sometimes mentioned as an infrared satellite, although it is a submillimeter satellite.

==== Infrared instruments on space telescopes ====

For many space telescopes, only some of the instruments are capable of infrared observation.  Below are listed some of the most notable of these space observatories and instruments:

* [[Cosmic Background Explorer]] (COBE) satellite (1989-1993) [[Diffuse Infrared Background Experiment]] (DIRBE) instrument
* [[Hubble Space Telescope]] (1990-) [[Near Infrared Camera and Multi-Object Spectrometer]] (NICMOS) instrument (1997-1999, 2002-2008)
* Hubble Space Telescope [[Wide Field Camera 3]] (WFC3) camera (2009-) observes infrared.

=== Airborne Observatories ===

Three airplane-based observatories have been used (other aircraft have also been used occasionally to host infrared space studies) to study the sky in infrared. They are:

* [[Kuiper Airborne Observatory|Galileo Observatory]], a [[NASA]] mission. Was active 1965-1973.
* [[Kuiper Airborne Observatory]], a [[NASA]] mission. Was active 1974-1995.
* [[SOFIA]], a [[NASA]]-[[German Aerospace Center|DLR]] mission. Was active 2010-2022.

=== Ground-based observatories ===

Many ground-based infrared telescopes exist around the world. The largest are:

* [[VISTA (telescope)|VISTA]]
* [[United Kingdom Infrared Telescope|UKIRT]]
* [[NASA Infrared Telescope Facility|IRTF]]
* [[Wyoming Infrared Observatory|WIRO]]

== See also ==
*[[Far-infrared astronomy]]
*[[Infrared spectroscopy]]
*[[List of largest infrared telescopes]]
*[[Radio Galaxy Zoo]]

==References==
{{reflist|refs=

<ref name="Price2008">{{cite journal
 | last1=Price | first1=Stephan D.
 | title=History of Space-Based Infrared Astronomy and the Air Force Infrared Celestial Backgrounds Program
 | journal=USAF Technical report | date=18 April 2008 | issue=AFRL-RV-HA-TR-2008-1039 | pages=1-348
 | url=https://users.physics.unc.edu/~gcsloan/library/2012/price/price08.pdf | access-date=4 April 2025}}</ref>

}}

==External links==
{{Commons category|Infrared astronomy}}

* [http://coolcosmos.ipac.caltech.edu/ Cool Cosmos (Caltech/IPAC IR educational resource site)]
* [http://irsa.ipac.caltech.edu Infrared Science Archive]

{{Astronomy navbox}}

{{Authority control}}

{{DEFAULTSORT:Infrared Astronomy}}
[[Category:Astronomical imaging]]
[[Category:Observational astronomy]]
[[Category:Infrared imaging]]