Difference between revisions of "Infrared astronomy" - New World Encyclopedia
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| − | + | '''Infrared astronomy''' is the branch of [[astronomy]] and [[astrophysics]] which deals with objects visible in [[infrared]] (IR) radiation. Visible radiation ranges from 400 [[nanometre|nm]] (blue) to 700 nm (red). Longer wavelengths than 700 nm but still shorter than [[microwaves]] are called infrared (or sometimes ''submillimeter'' waves). | |
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| − | '''Infrared astronomy''' is the branch of [[astronomy]] and [[astrophysics]] which deals with objects visible in [[infrared]] (IR) radiation. Visible radiation ranges from 400 [[ | ||
Scientists classify infrared astronomy as part of [[optical astronomy]] because optical components (mirrors, lenses and solid state digital detectors) are usually used. | Scientists classify infrared astronomy as part of [[optical astronomy]] because optical components (mirrors, lenses and solid state digital detectors) are usually used. | ||
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== Modern infrared astronomy == | == Modern infrared astronomy == | ||
| − | Near infrared radiation (infrared radiation with wavelengths close to that of visible light) behaves in a very similar way to visible light, and can be detected using similar electronic devices. For this reason, the near infrared region of the spectrum is commonly incorporated as part of the "optical" spectrum, along with the near ultraviolet (most scientific instruments such as optical telescopes cover the near-infrared as well as the visible). The [[far infrared]] extends to submillimeter wavelengths, which are observed by telescopes such as the [[James Clerk Maxwell Telescope]] at [[Mauna Kea Observatory]]. | + | Near infrared radiation (infrared radiation with wavelengths close to that of visible light) behaves in a very similar way to visible light, and can be detected using similar electronic devices. For this reason, the near infrared region of the spectrum is commonly incorporated as part of the "optical" spectrum, along with the near ultraviolet (most scientific instruments such as [[optical telescopes]] cover the near-infrared as well as the visible). The [[far infrared]] extends to submillimeter wavelengths, which are observed by telescopes such as the [[James Clerk Maxwell Telescope]] at [[Mauna Kea Observatory]]. |
| − | Like all other forms of [[electromagnetic radiation]], infrared is | + | Like all other forms of [[electromagnetic radiation]], infrared is utilised by [[astronomer]]s to learn more about the [[universe]]. As infrared is essentially heat radiation, infrared [[telescope]]s (which include most major optical telescopes as well as a few dedicated infrared telescopes) need to have their detectors shielded from heat and chilled with [[liquid nitrogen]] in order to actually form images. This is particularly important in the mid infrared and far infrared regions of the spectrum. The principal limitation on infrared sensitivity from ground-based telescopes is the water vapour in the Earth's atmosphere, which absorbs a significant amount of infrared radiation. For this reason most infrared telescopes are built in very dry places at high altitude (above most of the water vapour in the atmosphere). Suitable locations on [[Earth]] include [[Mauna Kea Observatory]] at 4205 meters above sea level, the [[Atacama_Large_Millimeter_Array|ALMA site]] at 5000 m in [[Chile]] and regions of high altitude ice-desert such as [[Dome C]] in [[Antarctic]]. |
However, as with visible-light telescopes, space is the ideal place for their use and most optical telescopes launched into space (such as the [[Hubble Space Telescope]]) can also perform infrared observations. The recently launched [[Spitzer Space Telescope]] is dedicated solely to infrared observations. | However, as with visible-light telescopes, space is the ideal place for their use and most optical telescopes launched into space (such as the [[Hubble Space Telescope]]) can also perform infrared observations. The recently launched [[Spitzer Space Telescope]] is dedicated solely to infrared observations. | ||
| − | Another way of doing infrared astronomy is by the use of airborne observatories | + | Another way of doing infrared astronomy is by the use of airborne observatories such as [[SOFIA]] (Stratospheric Observatory for Infrared Astronomy) and the [[Kuiper Airborne Observatory]]. |
| − | By flying | + | By flying at high altitude (Stratosphere) less water vapour will be between the telescope and space leading to a smaller IR absorption of the atmosphere.<BR> |
The residual IR background (due to the absorption left) is statically removed by applying a chopping reduction technique of the observed field and a blank region. | The residual IR background (due to the absorption left) is statically removed by applying a chopping reduction technique of the observed field and a blank region. | ||
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== Infrared technology == | == Infrared technology == | ||
| − | The cheapest infrared detectors commonly used at research telescopes are [[HgCdTe]] arrays. These operate well between 1 and 5 [[ | + | The cheapest infrared detectors commonly used at research telescopes are [[HgCdTe]] arrays. These operate well between 1 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 circuits and sometimes very high [[pixel]] counts. | Special requirements for infrared astronomy include: very low dark currents to allow long integration times, associated low noise readout circuits and sometimes very high [[pixel]] counts. | ||
== Astronomers' infrared spectrum == | == Astronomers' infrared spectrum == | ||
| − | Infrared space telescopes such as [[Spitzer Space Telescope|Spitzer]], [[IRAS]], [[Infrared_Space_Observatory|ISO]] and the forthcoming [[Herschel Space Observatory]] can observe across almost all of the infrared spectrum. However, most infrared astronomy is still done at ground-based telescopes, and these are limited to observations through a small number of spectral "windows, | + | Infrared space telescopes such as [[Spitzer Space Telescope|Spitzer]], [[IRAS]], [[Infrared_Space_Observatory|ISO]] and the forthcoming [[Herschel Space Observatory]] can observe across almost all of the infrared spectrum. However, most infrared astronomy is still done at ground-based telescopes, and these are limited to observations through a small number of spectral "windows", at wavelengths where the Earth's atmosphere is transparent. The main infrared windows are listed below: |
<table width=100% cellspacing=4 cellpadding=4> | <table width=100% cellspacing=4 cellpadding=4> | ||
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</tr> | </tr> | ||
<tr> | <tr> | ||
| − | <td valign=top align=left>([[ | + | <td valign=top align=left>([[micrometre]]s)</td><td></td><td></td> |
</tr> | </tr> | ||
<tr> | <tr> | ||
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== See also == | == See also == | ||
| − | |||
* [[Far infrared astronomy]] | * [[Far infrared astronomy]] | ||
| − | * Most telescopes listed in [[:Category:Telescopes]] can observe at some infrared wavelengths | + | * [[Infrared spectroscopy]] |
| + | <!--[looks misplaced for this section; category should be supplanted with the specific ones]* Most telescopes listed in [[:Category:Telescopes]] can observe at some infrared wavelengths—> | ||
* [[Infrared]] | * [[Infrared]] | ||
* [[Infrared detector]] | * [[Infrared detector]] | ||
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==External links== | ==External links== | ||
| − | * [http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/ Caltech IR tutorial] | + | * [http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/ Caltech IR tutorial] |
| − | * [http://cfa-www.harvard.edu/cfa/oir/ Harvard Optical and Infrared Astronomy Group] | + | * [http://cfa-www.harvard.edu/cfa/oir/ Harvard Optical and Infrared Astronomy Group] |
[[Category:Physical sciences]] | [[Category:Physical sciences]] | ||
[[Category:Astronomy]] | [[Category:Astronomy]] | ||
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| − | {{ | + | {{credit|207862507}} |
Revision as of 13:50, 8 May 2008
Infrared astronomy is the branch of astronomy and astrophysics which deals with objects visible in infrared (IR) radiation. Visible radiation ranges from 400 nm (blue) to 700 nm (red). Longer wavelengths than 700 nm but still shorter than microwaves are called infrared (or sometimes submillimeter waves).
Scientists classify infrared astronomy as part of optical astronomy because optical components (mirrors, lenses and solid state digital detectors) are usually used.
Discovery
After the use of prisms by Isaac Newton to split white light into a spectrum, it was found in 1800 by William Herschel that the hottest part of the band of light from the Sun was actually past the red end of the spectrum. These "heat rays" even displayed some spectral lines. Charles Piazzi Smyth in 1856 detected infrared radiation in the light of the Moon.
Modern infrared astronomy
Near infrared radiation (infrared radiation with wavelengths close to that of visible light) behaves in a very similar way to visible light, and can be detected using similar electronic devices. For this reason, the near infrared region of the spectrum is commonly incorporated as part of the "optical" spectrum, along with the near ultraviolet (most scientific instruments such as optical telescopes cover the near-infrared as well as the visible). The far infrared extends to submillimeter wavelengths, which are observed by telescopes such as the James Clerk Maxwell Telescope at Mauna Kea Observatory.
Like all other forms of electromagnetic radiation, infrared is utilised by astronomers to learn more about the universe. As infrared is essentially heat radiation, infrared telescopes (which include most major optical telescopes as well as a few dedicated infrared telescopes) need to have their detectors shielded from heat and chilled with liquid nitrogen in order to actually form images. This is particularly important in the mid infrared and far infrared regions of the spectrum. The principal limitation on infrared sensitivity from ground-based telescopes is the water vapour in the Earth's atmosphere, which absorbs a significant amount of infrared radiation. For this reason most infrared telescopes are built in very dry places at high altitude (above most of the water vapour in the atmosphere). Suitable locations on Earth include Mauna Kea Observatory at 4205 meters above sea level, the ALMA site at 5000 m in Chile and regions of high altitude ice-desert such as Dome C in Antarctic.
However, as with visible-light telescopes, space is the ideal place for their use and most optical telescopes launched into space (such as the Hubble Space Telescope) can also perform infrared observations. The recently launched Spitzer Space Telescope is dedicated solely to infrared observations.
Another way of doing infrared astronomy is by the use of airborne observatories such as SOFIA (Stratospheric Observatory for Infrared Astronomy) and the Kuiper Airborne Observatory.
By flying at high altitude (Stratosphere) less water vapour will be between the telescope and space leading to a smaller IR absorption of the atmosphere.
The residual IR background (due to the absorption left) is statically removed by applying a chopping reduction technique of the observed field and a blank region.
The highest resolution infrared observations are performed by ground-based astronomical interferometers.
Infrared technology
The cheapest infrared detectors commonly used at research telescopes are HgCdTe arrays. These operate well between 1 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 circuits and sometimes very high pixel counts.
Astronomers' infrared spectrum
Infrared space telescopes such as Spitzer, IRAS, ISO and the forthcoming Herschel Space Observatory can observe across almost all of the infrared spectrum. However, most infrared astronomy is still done at ground-based telescopes, and these are limited to observations through a small number of spectral "windows", at wavelengths where the Earth's atmosphere is transparent. The main infrared windows are listed below:
| Wavelength range | Astronomical bands | Telescopes |
|---|---|---|
| (micrometres) | ||
| 0.65 to 1.0 | R and I bands | All major optical telescopes |
| 1.25 | J band | Most major optical telescopes and most dedicated infrared telescopes |
| 1.65 | H band | Most major optical telescopes and most dedicated infrared telescopes |
| 2.2 | K band | Most major optical telescopes and most dedicated infrared telescopes |
| 3.45 | L band | Most dedicated infrared telescopes and some optical telescopes |
| 4.7 | M band | Most dedicated infrared telescopes and some optical telescopes |
| 10 | N band | Most dedicated infrared telescopes and some optical telescopes |
| 20 | Q band | Some dedicated infrared telescopes and some optical telescopes |
| 450 | submillimeter | Submillimeter telescopes |
Between these windows there are generally regions where infrared observations are more difficult or impossible from the ground due to the opacity of the atmosphere. Dedicated infrared and submillimeter telescopes are generally built at very high altitude sites like Mauna Kea Observatory, Hawaii and the ALMA site in Chile, or even flown on aircraft like SOFIA, providing the best sensitivity available from Earth based observatories. Data from space-based observatories like Spitzer, IRAS and ISO help fill in the gaps between the atmospheric windows listed above.
See also
- Far infrared astronomy
- Infrared spectroscopy
- Infrared
- Infrared detector
- Radio window
- Atmospheric window
- Astronomical window
- Optical window
External links
Credits
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