A Wolter telescope is a
telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...
for
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
s that only uses grazing incidence optics – mirrors that reflect
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
s at very shallow angles.
Problems with conventional telescope designs
Conventional
telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...
designs require reflection or refraction in a manner that does not work well for X-rays. Visible light optical systems use either lenses or mirrors aligned for nearly normal incidence – that is, the light waves travel nearly perpendicular to the reflecting or refracting surface. Conventional mirror telescopes work poorly with X-rays, since X-rays that strike mirror surfaces nearly perpendicularly are either transmitted or absorbed – not reflected.
Lenses for visible light are made of transparent materials with an
index of refraction
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
substantially different from 1, but all known X-ray-transparent materials have index of refraction essentially the same as 1, so X-ray lenses are not practical.
X-ray mirror telescope design
X-ray mirrors can be built, but only if the angle from the plane of reflection is very low (typically 10 arc-minutes to 2 degrees).
These are called ''glancing'' (or ''grazing'') ''incidence mirrors''. In 1952,
Hans Wolter Hans Wolter (11 May 1911 in Dramburg – 17 August 1978 in Marburg) was a German physicist who designed an aplanatic system of grazing incidence mirrors that satisfied the Abbe sine condition (i.e. free of both spherical aberration and coma).
Wolte ...
outlined three ways a telescope could be built using only this kind of mirror.
These are called Wolter telescopes of type I, II, and III.
Each has different advantages and disadvantages.
Wolter's key innovation was that by using two mirrors it is possible to create a telescope with a usably wide field of view. In contrast, a grazing incidence telescope with just one parabolic mirror could focus X-rays, but only very close to the centre of the field of view. The rest of the image would suffer from extreme
coma
A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
.
See also
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List of telescope types
The following are lists of devices categorized as types of telescopes or devices associated with telescopes. They are broken into major classifications with many variations due to professional, amateur, and commercial sub-types. Telescopes can be ...
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Nuclear Spectroscopic Telescope Array
NuSTAR (Nuclear Spectroscopic Telescope Array, also named Explorer 93 and SMEX-11) is a NASA space-based X-ray telescope that uses a conical approximation to a Wolter telescope to focus high energy X-rays from astrophysical sources, especiall ...
(NuSTAR) (2012+)
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Swift Gamma-Ray Burst Mission Contains a Wolter Type-I X-ray telescope (2004+)
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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 ...
Orbiting observatory using a Wolter X-ray telescope. (1999+)
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XMM-Newton
''XMM-Newton'', also known as the High Throughput X-ray Spectroscopy Mission and the X-ray Multi-Mirror Mission, is an X-ray space observatory launched by the European Space Agency in December 1999 on an Ariane 5 rocket. It is the second cornerst ...
Orbiting X-ray observatory using a Wolter Type-I X-ray telescope. (1999+)
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ROSAT Orbiting X-ray observatory (1990-1999)
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eROSITA Orbiting X-ray observatory using Wolter Type-I X-ray telescope on board
Spektr-RG
Spektr-RG (Russian: Спектр-РГ, ''Spectrum'' + '' Röntgen'' + ''Gamma''; also called Spectrum-X-Gamma, SRG, SXG) is a Russian–German high-energy astrophysics space observatory which was launched on 13 July 2019. It follows on from th ...
(SRG) (2019+)
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ART-XC Orbiting X-ray observatory using Wolter Type-I X-ray telescope on board
Spektr-RG
Spektr-RG (Russian: Спектр-РГ, ''Spectrum'' + '' Röntgen'' + ''Gamma''; also called Spectrum-X-Gamma, SRG, SXG) is a Russian–German high-energy astrophysics space observatory which was launched on 13 July 2019. It follows on from th ...
(SRG)(2019+)
*
ATHENA
Athena or Athene, often given the epithet Pallas, is an ancient Greek goddess associated with wisdom, warfare, and handicraft who was later syncretized with the Roman goddess Minerva. Athena was regarded as the patron and protectress of v ...
(2031+)
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Neutron microscope
References
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{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System
X-ray instrumentation
X-ray telescopes