A solar telescope is a special purpose
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 ...
used to observe the
Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, the
visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called '' visible light'' or simply light. A typical human eye will respond to ...
. Obsolete names for Sun telescopes include heliograph and photoheliograph.
Professional solar telescopes
Solar telescopes need optics large enough to achieve the best possible
diffraction limit but less so for the associated light-collecting power of other astronomical telescopes. However, recently newer narrower
filters
Filter, filtering or filters may refer to:
Science and technology
Computing
* Filter (higher-order function), in functional programming
* Filter (software), a computer program to process a data stream
* Filter (video), a software component that ...
and higher framerates have also driven solar telescopes towards photon-starved operations. Both the
Daniel K. Inouye Solar Telescope as well as the proposed
European Solar Telescope (EST) have larger apertures not only to increase the resolution, but also to increase the light-collecting power.
Because solar telescopes operate during the day, seeing is generally worse than for night-time telescopes, because the ground around the telescope is heated which causes
turbulence and degrades the resolution. To alleviate this, solar telescopes are usually built on towers and the structures are painted white. The
Dutch Open Telescope is built on an open framework to allow the wind to pass through the complete structure and provide cooling around the telescope's main mirror.
Another solar telescope-specific problem is the heat generated by the tightly-focused sunlight. For this reason, a
heat stop is an integral part of the design of solar telescopes. For the
Daniel K. Inouye Solar Telescope, the heat load is 2.5 MW/m
2, with peak powers of 11.4 kW. The goal of such a heat stop is not only to survive this heat load, but also to remain cool enough not to induce any additional turbulence inside the telescope's dome.
Professional solar observatories may have main optical elements with very long
focal lengths (although not always,
Dutch Open Telescope) and light paths operating in a
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
or
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
to eliminate air motion due to
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...
inside the telescope. However, this is not possible for apertures over 1 meter, at which the pressure difference at the entrance window of the vacuum tube becomes too large. Therefore, the
Daniel K. Inouye Solar Telescope and the
EST have active cooling of the dome to minimize the temperature difference between the air inside and outside the telescope.
Due to the suns narrow path across the sky, some solar telescopes are fixed in position (and are sometimes buried underground), with the only moving part being a
heliostat
A heliostat (from '' helios'', the Greek word for ''sun'', and ''stat'', as in stationary) is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating ...
to track the Sun. One example of this is the
McMath-Pierce Solar Telescope.
Selected solar telescopes
* The
Einstein Tower (''Einsteinturm'') became operational in 1924
*
McMath-Pierce Solar Telescope (1.6 m diameter, 1961–)
*
Andrei Severny Solar Telescope
Andrei, Andrey or Andrej (in Cyrillic script: Андрэй , Андрей or Андреј) is a form of Andreas/Ἀνδρέας in Slavic languages and Romanian. People with the name include:
*Andrei of Polotsk (–1399), Lithuanian nobleman
*An ...
(90 cm diameter, 1954–) in
Crimea
Crimea, crh, Къырым, Qırım, grc, Κιμμερία / Ταυρική, translit=Kimmería / Taurikḗ ( ) is a peninsula in Ukraine, on the northern coast of the Black Sea, that has been occupied by Russia since 2014. It has a p ...
*
Multi-purpose automated solar telescope (80 cm diameter) in Republic of Buryatia, Russia
*
Large solar vacuum telescope (76 cm diameter, 1980-) on the coast of lake Baikal, Russia
*
McMath-Hulbert Observatory (24"/61 cm diameter, 1941–1979)
*
Swedish Vacuum Solar Telescope (47.5 cm diameter, 1985–2000)
*
Swedish 1-m Solar Telescope (1 m diameter, 2002–)
*
Richard B. Dunn Solar Telescope (0.76 m diameter, 1969–)
*
Mount Wilson Observatory
*
Dutch Open Telescope (45 cm diameter, 1997–)
* The
Teide Observatory hosts multiple solar telescopes, including
** the 70 cm
Vacuum Tower Telescope (1989–) and
** the 1.5 m
GREGOR Solar Telescope (2012–]).
*
Goode Solar Telescope (1.6 m, 2009-)
* Chinese Large Solar Telescope (CLST) (180 cm diameter, 2019–)
*
Daniel K. Inouye Solar Telescope (DKIST), a telescope with 4m aperture.
*
European Solar Telescope
The European Solar Telescope (EST) is a pan-European project to build a next-generation 4-metre class solar telescope, to be located at the Roque de los Muchachos Observatory in the Canary Islands, Spain. It will use state-of-the-art instruments ...
(EST), a proposed 4-meter class aperture telescope.
*
Chinese Giant Solar Telescope (CGST), a proposed 5-8 meter aperture telescope.
*
National Large Solar Telescope
The National Large Solar Telescope (NLST) is a Gregorian multi-purpose open telescopeHasan, S. S. The Indian National Large Solar TelescopSolar and Stellar Variability: Impact on Earth and Planets, Proceedings of the International Astronomical ...
(NLST), is a Gregorian multi-purpose open telescope proposed to be built and installed in India and aims to study the Sun's microscopic structure.
Other types of observation
Most solar observatories observe optically at visible, UV, and near infrared wavelengths, but other solar phenomena can be observed — albeit not from the Earth's surface due to the
absorption
Absorption may refer to:
Chemistry and biology
*Absorption (biology), digestion
**Absorption (small intestine)
*Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials
*Absorption (skin), a route by which s ...
of the atmosphere:
* Solar X-ray astronomy, observations of the Sun in x-rays
* Multi-spectral solar telescope array (
MSSTA), a rocket launched payload of UV telescopes in the 1990s
*
Leoncito Astronomical Complex operated a submillimeter wavelength solar telescope.
* The
Radio Solar Telescope Network (RSTN) is a network of solar observatories maintained and operated by the U.S.
Air Force Weather Agency
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
.
*
CERN Axion Solar Telescope
The CERN Axion Solar Telescope (CAST) is an experiment in astroparticle physics to search for axions originating from the Sun. The experiment, sited at CERN in Switzerland, was commissioned in 1999 and came online in 2002 with the first data ...
(CAST), looks for solar
axions in the early 2000s
Amateur solar telescopes
In the field of
amateur astronomy there are many methods used to observe the Sun. Amateurs use everything from simple systems to project the Sun on a piece of white paper, light blocking
filters
Filter, filtering or filters may refer to:
Science and technology
Computing
* Filter (higher-order function), in functional programming
* Filter (software), a computer program to process a data stream
* Filter (video), a software component that ...
,
Herschel wedge
A Herschel wedge or Herschel prism is an optical prism used in solar observation to refract most of the light out of the optical path, allowing safe visual observation. It was first proposed and used by astronomer John Herschel in the 1830s.
Ov ...
s which redirect 95% of the light and heat away from the eyepiece,
up to
hydrogen-alpha filter systems and even home built
spectrohelioscopes. In contrast to professional telescopes, amateur solar telescopes are usually much smaller.
With a conventional telescope, an extremely dark filter at the opening of the primary tube is used to reduce the light of the sun to tolerable levels. Since the full available spectrum is observed, this is known as "white-light" viewing, and the opening filter is called a "white-light filter". The problem is that even reduced, the full spectrum of white light tends to obscure many of the specific features associated with solar activity, such as prominences and details of the
chromosphere (i.e., the surface). Specialized solar telescopes facilitate clear observation of such H-alpha emissions by using a bandwidth filter implemented with a
Fabry-Perot etalon.
[Morison, Ian (2016-12-25). H-alpha Solar Telescopes - An In-depth Discussion and Survey. Professor Morison's Astronomy Digest, 25 December 2016. Retrieved on 2020-04-17 from http://www.ianmorison.com/h-alpha-solar-telescopes-an-in-depth-discussion-and-survey/.]
See also
*
List of solar telescopes
This is a list of solar telescopes built in various countries around the world. A solar telescope is a specialized telescope that is used to observe the Sun.
This list contains ground-based professional observatory telescopes at optical wavelengt ...
*
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 ...
*
Heliostat
A heliostat (from '' helios'', the Greek word for ''sun'', and ''stat'', as in stationary) is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating ...
References
External links
* *
CSIRO Solar Heliographpart 2
Solar Gallery of an amateur astronomer
Solar Gallery of the Hong Kong Astronomical Society
*
{{Authority control
Astronomical instruments
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 ...