The Daniel K. Inouye Solar Telescope (DKIST) is a scientific facility for studies of 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 Haleakala Observatory on the

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

an island of

Maui Maui (; Hawaiian language, Hawaiian: ) is the second largest island in the Hawaiian archipelago, at 727.2 square miles (1,883 km2). It is the List of islands of the United States by area, 17th-largest in the United States. Maui is one of ...

. Known as the Advanced Technology Solar Telescope (ATST) until 2013, it was named after Daniel K. Inouye, a US Senator for Hawaii. It is the world's largest

solar telescope A solar telescope or a solar observatory is a special-purpose telescope used to observe the Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, the visible spectrum. Obsolete names for Sun telescopes include helio ...

, with a 4-meter aperture. The DKIST is funded by

National Science Foundation The U.S. National Science Foundation (NSF) is an Independent agencies of the United States government#Examples of independent agencies, independent agency of the Federal government of the United States, United States federal government that su ...

and managed by the

National Solar Observatory The National Solar Observatory (NSO) is a United States federally funded research and development center to advance the knowledge of the physics of the Sun. NSO studies the Sun both as an astronomical object and as the dominant external influen ...

. The total project cost is $344.13 million. It is a collaboration of numerous research institutions. Some test images were released in January 2020. The end of construction and transition into scientific observations was announced in November 2021. The DKIST can observe the Sun in visible to near-infrared wavelengths and has a 4.24-meter

primary mirror A primary mirror (or primary) is the principal light-gathering surface (the objective) of a reflecting telescope. Description The primary mirror of a reflecting telescope is a spherical, parabolic, or hyperbolic shaped disks of polished ...

in an off-axis Gregorian configuration that provides a 4-meter clear, unobstructed

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

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 ...

correct for atmospheric

distortions In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...

and blurring of the solar image, which enables high-resolution observations of features on the

as small as . The off-axis, clear aperture design avoids a central obstruction, minimizing scattered light. It also eases operation of

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 ...

and digital image reconstruction such as

speckle imaging Speckle imaging comprises a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add ("' ...

. The site on the

Haleakalā Haleakalā (; Hawaiian: ), or the East Maui Volcano, is a massive, active shield volcano that forms more than 75% of the Hawaiian Islands, Hawaiian Island of Maui. The western 25% of the island is formed by another volcano, Mauna Kahalawai, als ...

volcano was selected for its clear daytime weather and favourable atmospheric seeing conditions. It commenced its first science observations on February 23, 2022, signaling the start of its year-long operations commissioning phase.

Construction

The contract to build the

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

was awarded in 2010, with a then-planned completion date of 2017. Physical construction at the DKIST site began in January 2013, and work on the telescope housing was completed in September 2013. The primary mirror was delivered to the site the night of 1–2 August 2017 and the completed telescope provided images of the sun in unprecedented detail in December 2019. Further instruments, to measure the Sun's magnetic field, were to be added in the first half of 2020. Completion of construction and transition into operational phase with the first scientific observations was announced on November 22, 2021. At the time, the telescope had been over 25 years in the making (including preliminary design etc. not just the building).

Main telescope structure

Telescope Mount Assembly of the Inouye Solar Telescope

The 75 mm thick f/2 primary mirror is 4.24 meters in diameter with the outer 12 cm masked, leaving a 4-meter off-axis section of a 12-meter diameter, f/0.67 concave parabola. It was cast from

Zerodur Zerodur is a lithium-aluminosilicate glass-ceramic manufactured by Schott AG. Zerodur has a near zero coefficient of thermal expansion (CTE), and is used for high-precision applications in telescope optics, microlithography machines and inert ...

by Schott and polished at the Richard F. Caris Mirror Laboratory of the

University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a Public university, public Land-grant university, land-grant research university in Tucson, Arizona, United States. Founded in 1885 by the 13th Arizona Territorial Legislature, it ...

and aluminized by the

AMOS Amos or AMOS may refer to: Arts and entertainment * ''Amos'' (album), an album by Michael Ray * Amos (band), an American Christian rock band * ''Amos'' (film), a 1985 American made-for-television drama film * Amos (guitar), a 1958 Gibson Fl ...

mirror coating facility. The 0.65-meter

secondary mirror A secondary mirror (or secondary) is the second deflecting or focusing mirror element in a reflecting telescope. Light gathered by the primary mirror is directed towards a focal point typically past the location of the secondary. Secondary mirro ...

, a concave

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

with a focal length of 1 meter, was made from

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...

and is mounted on a hexapod to compensate for

thermal expansion Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temp ...

and bending of the telescope structure keeping the mirror in its optimal position.

Adaptive and active optics

One key component of the DKIST is its adaptive and

active optics Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, and mechanical stress. Without active op ...

system, which is responsible for correcting distortions in the telescope's images caused by the Earth's atmosphere. These distortions, known as "seeing," can be caused by temperature gradients and other factors in the atmosphere and can significantly degrade the quality of telescope images. The DKIST's adaptive optics system uses a

deformable mirror Deformable mirrors (DM) are mirrors whose surface can be deformed, in order to achieve wavefront control and correction of optical Optical aberration, aberrations. Deformable mirrors are used in combination with wavefront sensors and real-time con ...

, which can be adjusted in real-time to correct for atmospheric distortions. The system also includes a

wavefront sensor In physics, the wavefront of a time-varying ''wave field'' is the set ( locus) of all points having the same ''phase''. The term is generally meaningful only for fields that, at each point, vary sinusoidally in time with a single temporal frequ ...

, which measures the distortions in the incoming light and feeds this information back to the deformable mirror to make the necessary adjustments. The active optics system, on the other hand, is responsible for maintaining the telescope's focus and alignment. It uses a network of sensors and

actuators An actuator is a component of a machine that produces force, torque, or displacement, when an electrical, pneumatic or hydraulic input is supplied to it in a system (called an actuating system). The effect is usually produced in a controlled way. ...

to constantly monitor and adjust the position of the telescope's mirrors, ensuring that they remain properly aligned and focused. Together, the adaptive and active optics systems allow the DKIST to produce some of the highest-resolution images of the Sun ever taken. These images can be used to study the Sun's surface and atmosphere in greater detail, helping scientists to better understand the processes that drive solar activity and space weather.

Instrumentation

DKIST is expected to have five first-generation instruments.

Visible Broadband Imager (VBI)

The VBI is a

diffraction-limited In optics, any optical instrument or systema microscope, telescope, or camerahas a principal limit to its resolution due to the physics of diffraction. An optical instrument is said to be diffraction-limited if it has reached this limit of res ...

two-channel imager, with each path made of an

interference filter An interference filter, dichroic filter, or thin-film filter is an optical filter that Reflection (physics), reflects some wavelengths (colors) of light and transmits others, with almost no absorption (optics), absorption for all wavelengths of i ...

and a digital scientific

CMOS sensor An active-pixel sensor (APS) is an image sensor, which was invented by Peter J.W. Noble in 1968, where each pixel sensor unit cell has a photodetector (typically a pinned photodiode) and one or more active transistors. In a metal–oxide–semic ...

camera that samples the image of the Sun. Each camera features 4k×4k pixels. The interference filters work as a

band-pass filter A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects ( attenuates) frequencies outside that range. It is the inverse of a '' band-stop filter''. Description In electronics and s ...

that only transmits a selected

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

range (i.e. color) of the sunlight. Four different interference filters are available in each channel that are mounted in a motorized fast-change filter wheel. VBI blue channel (45

″ The prime symbol , double prime symbol , triple prime symbol , and quadruple prime symbol are used to designate units and for other purposes in mathematics, science, linguistics and music. Although the characters differ little in appearance fr ...

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 ...

) * 393.327 nm,

FWHM In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve ...

: 0.101 nm ( Ca II K

spectral line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency ...

, dark-violet) * 430.520 nm, FWHM: 0.437 nm (G-band, violet) * 450.287 nm, FWHM: 0.41 nm (blue continuum) * 486.139 nm, FWHM: 0.0464 nm (

H-beta The Balmer series, or Balmer lines in atomic physics, is one of a set of six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is calculated using the Balmer formula, an empirical equation discovered b ...

turquoise Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula . It is rare and valuable in finer grades and has been prized as a gemstone for millennia due to its hue. The robi ...

) VBI red channel (69

) * 656.282 nm, FWHM: 0.049 nm (

H-alpha Hydrogen-alpha, typically shortened to H-alpha or Hα, is a deep-red visible spectral line of the hydrogen atom with a wavelength of 656.28 nm in air and 656.46 nm in vacuum. It is the first spectral line in the Balmer series and is em ...

, light-red) * 668.423 nm, FWHM: 0.442 nm (red continuum) * 705.839 nm, FWHM: 0.578 nm ( Titanium(II) oxide (TiO)

, dark-red) * 789.186 nm, FWHM: 0.356 nm ( Fe XI

) Per wavelength, a burst of images shall be recorded with high frame rate (30 fps), digitally analyzed and formed into a single sharpened image ( speckle-reconstruction). VBI is fabricated by the

Visible Spectro-Polarimeter (ViSP)

ViSP is fabricated by the

High Altitude Observatory The High Altitude Observatory (HAO) is a laboratory of the US National Center for Atmospheric Research (NCAR). HAO operates the Mauna Loa Solar Observatory on Hawaii (island), Hawaii and a research institute in Boulder, Colorado. Its staff condu ...

Visible Tunable Filter (VTF)

VTF is fabricated by the Kiepenheuer-Institut für Sonnenphysik.

Diffraction-Limited Near-InfraRed Spectro-Polarimeter (DL-NIRSP)

DL-NIRSP is a

diffraction grating In optics, a diffraction grating is an optical grating with a periodic structure that diffraction, diffracts light, or another type of electromagnetic radiation, into several beams traveling in different directions (i.e., different diffractio ...

based

integral field spectrograph Integral field spectrographs (IFS) combine spectrographic and imaging capabilities in the optical or infrared wavelength domains (0.32 μm – 24 μm) to get from a single exposure spatially resolved Spectrum, spectra in a bi-dimensional region. T ...

with a

spectral resolution The spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum. It is usually denoted by \Delta\lambda, and is closely related to the resolvi ...

R=250000. DL-NIRSP is fabricated by Institute for Astronomy (IfA) of the

University of Hawaii A university () is an educational institution, institution of tertiary education and research which awards academic degrees in several Discipline (academia), academic disciplines. ''University'' is derived from the Latin phrase , which roughly ...

Cryogenic Near-InfraRed Spectro-Polarimeter (Cryo-NIRSP)

Cryo-NIRSP is fabricated by Institute for Astronomy (IfA) of the

Partners

, twenty-two institutions had joined the collaboration building DKIST: * Corporate Office:

Association of Universities for Research in Astronomy The Association of Universities for Research in Astronomy (AURA) is a consortium of universities and other institutions that operates astronomical observatories and telescopes. Founded October 10, 1957, with the encouragement of the National Sc ...

* Funding Agency:

* Principal Investigator:

* Co-Principal Investigators: **

New Jersey Institute of Technology New Jersey Institute of Technology (NJIT) is a Public university, public research university in Newark, New Jersey, United States, with a graduate-degree-granting satellite campus in Jersey City. Founded in 1881 with the support of local indust ...

**Institute for Astronomy,

**Department of Astronomy and Astrophysics and Department of Mathematics,

University of Chicago The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...

* Collaborators: **

Air Force Research Laboratory The Air Force Research Laboratory (AFRL) is a scientific research and development detachment of the United States Air Force Air Force Materiel Command, Materiel Command dedicated to leading the discovery, development, and integration of direct- ...

**Bellan Plasma Group, Laboratories of Applied Physics,

California Institute of Technology The California Institute of Technology (branded as Caltech) is a private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small group of institutes ...

**Department of Physics and Astronomy, California State University at Northridge ** Colorado Research Associates ** Center for Astrophysics Harvard & Smithsonian ** Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany **

Lockheed Martin Solar and Astrophysics Laboratory The Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) is part of the Lockheed Martin Advanced Technology Center (ATC) that is known primarily for its scientific work in the field of solar physics, astronomy and space weather. The LMSAL tea ...

**Department of Physics and Astronomy,

Michigan State University Michigan State University (Michigan State or MSU) is a public university, public Land-grant university, land-grant research university in East Lansing, Michigan, United States. It was founded in 1855 as the Agricultural College of the State o ...

**Department of Physics,

Montana State University Montana State University (MSU) is a public land-grant research university in Bozeman, Montana, United States. It enrolls more students than any other college or university in the state. MSU offers baccalaureate degrees in 60 fields, master's d ...

NASA Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C., in Greenbelt, Maryland, United States. Established on May 1, 1959, as NASA's first space flight center, GSFC ...

** NASA Marshall Space Flight Center **Plasma Physics Laboratory,

Princeton University Princeton University is a private university, private Ivy League research university in Princeton, New Jersey, United States. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial ...

**Instrumentation and Space Research Division,

Southwest Research Institute Southwest Research Institute (SwRI), headquartered in San Antonio, Texas, is an independent and nonprofit applied research and development (R&D) organization. Founded in 1947 by oil businessman Tom Slick, it provides contract research and deve ...

**W.W. Hansen Experimental Physics Laboratory,

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...

University of California Los Angeles The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California, United States. Its academic roots were established in 1881 as a normal school then known as the southern branch of the Cal ...

**Center for Astrophysics and Space Sciences,

University of California, San Diego The University of California, San Diego (UC San Diego in communications material, formerly and colloquially UCSD) is a public university, public Land-grant university, land-grant research university in San Diego, California, United States. Es ...

**Center for Astrophysics and Space Astronomy and Joint Institute for Laboratory Astrophysics,

University of Colorado at Boulder The University of Colorado Boulder (CU Boulder, CU, or Colorado) is a Public university, public research university in Boulder, Colorado, United States. Founded in 1876, five months before Colorado became a Federated state, state, it is the fla ...