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Solar telescope

A solar telescope is a specialized optical instrument designed exclusively for observing the Sun, distinguished from conventional astronomical telescopes by its adaptations to manage the overwhelming brightness, heat, and proximity of our star, enabling detailed study of solar phenomena without distortion from atmospheric turbulence or thermal gradients.^[1]^[2] These telescopes typically incorporate a heliostat—a tracking mirror system that redirects sunlight into a fixed optical path—often along a tall tower structure to achieve exceptionally long focal lengths, sometimes exceeding 100 meters, which magnifies solar features for high-resolution imaging.^[3]^[4] To counteract image blurring caused by air heated by concentrated sunlight, many employ vacuum tubes or evacuated enclosures that eliminate convective currents, while others use temperature-controlled optics or helium-filled chambers for similar effects.^[3]^[2] Additional features include narrowband filters to isolate specific wavelengths, adaptive optics for real-time atmospheric correction, and off-axis designs to minimize scattered light, all supporting observations across the visible, ultraviolet, and infrared spectra.^[1]^[5] The primary purpose of solar telescopes is to investigate the Sun's dynamic processes, including sunspots, magnetic fields, flares, prominences, and coronal mass ejections, which drive space weather and influence Earth's magnetosphere, ionosphere, and climate.^[6] By resolving features as small as 50 kilometers across the solar disk—equivalent to structures the size of a U.S. state—they facilitate measurements of solar magnetic activity, plasma flows, and energy transport, contributing to models of stellar evolution and predictions of solar-terrestrial interactions.^[7]^[8] Solar telescopes trace their origins to the early 20th century, when astronomer George Ellery Hale constructed pioneering instruments like the 1904 Snow Solar Telescope at Mount Wilson Observatory, followed by larger tower designs such as the 60-foot (1908) and 150-foot (1912) solar towers there, which introduced vertical configurations to leverage stable air at altitude.^[9]^[10] Mid-century advancements included vacuum tower telescopes, exemplified by the Richard B. Dunn Solar Telescope (dedicated 1969) at Sacramento Peak, which used an underground vacuum path for unprecedented clarity.^[3]^[11] The McMath-Pierce Solar Telescope (1962) at Kitt Peak National Observatory became the world's largest at the time with its 1.6-meter heliostat, emphasizing spectroscopic studies.^[12] Modern milestones feature the 1-meter Swedish 1-m Solar Telescope (2002) and the 4-meter Daniel K. Inouye Solar Telescope (2021) on Maui, Hawaii, which holds the record for the largest solar aperture and delivers diffraction-limited views resolving features down to 20 kilometers.^[2]^[7] Ongoing developments emphasize larger apertures, advanced instrumentation like spectro-polarimeters, and integration with space-based observatories such as NASA's Solar Dynamics Observatory, enhancing our understanding of the Sun's role in the heliosphere and beyond.^[13]

Introduction and History

Definition and Purpose

A solar telescope is a specialized optical instrument designed exclusively for observing the Sun, typically operating in visible, ultraviolet, or infrared wavelengths to study solar phenomena without damaging equipment or observers.^[6] Unlike general astronomical telescopes, which observe faint night-sky objects, solar telescopes are engineered to capture high-resolution images and spectra of the Sun's dynamic features.^[7] The use of telescopes for solar observation dates back to the 17th century, when early instruments first recorded sunspots.^[14] The primary purpose of solar telescopes is to enable detailed imaging and spectroscopy of the solar surface, known as the photosphere, as well as the overlying atmosphere, including the chromosphere and corona, along with the Sun's magnetic fields.^[7] These capabilities are essential for heliophysics research, which investigates solar activity, space weather events, and solar-terrestrial interactions that influence Earth's environment. By providing unprecedented views of solar processes, such telescopes support predictions of phenomena that affect satellite operations, power infrastructure, and global communications.^[15] Solar telescopes face unique challenges due to the Sun's extremely intense brightness and heat, which can overwhelm standard optical systems and pose risks to both instruments and human observers.^[6] To address this, they incorporate narrowband filters, such as those tuned to the hydrogen-alpha (H-alpha) or calcium-K spectral lines, which isolate specific wavelengths to reduce light intensity while highlighting key solar features like prominences and flares.^[16] Advanced heat rejection mechanisms, including cooling systems and off-axis designs, further protect the optics from thermal damage.^[17] Through these observations, solar telescopes contribute to a deeper understanding of solar cycles, explosive flares, looping prominences, and coronal mass ejections (CMEs), all of which drive space weather that can disrupt Earth's climate patterns, radio communications, and electrical grids.^[15] This research is vital for mitigating the societal impacts of solar events, such as geomagnetic storms that threaten technology-dependent infrastructure.^[18]

Historical Development

The earliest telescopic observations of the Sun were made in the early 17th century using simple refracting telescopes, with Galileo Galilei among the pioneers who systematically documented sunspots starting in 1610. These observations, conducted by projecting the Sun's image onto a surface to avoid direct viewing, revealed dark spots moving across the solar disk, providing evidence of the Sun's rotation with a period of about 27 days and challenging the Aristotelian view of perfect celestial bodies.^[19]^[20] In the 19th century, advancements enabled more detailed spectroscopic studies, including the invention of the spectroheliograph by George Ellery Hale in 1889, which allowed imaging the Sun in specific wavelengths to reveal chromospheric features. During this period, solar prominences—bright, gaseous structures extending from the Sun's surface—were first observed outside of total eclipses using spectroscopy, beginning with Pierre Janssen and Norman Lockyer in 1868, with Angelo Secchi contributing detailed records starting in 1871.^[21]^[22] The early 20th century marked the establishment of dedicated solar observatories, such as the Mount Wilson Solar Observatory founded by Hale in 1904, which featured the Snow Solar Telescope in 1905 and the 60-foot tower telescope completed in 1908. These facilities introduced coelostats—rotating mirrors that track the Sun and direct its light to a fixed horizontal optical path—for stable, high-resolution imaging without moving the main telescope structure.^[23]^[9] By the mid-20th century, efforts to mitigate atmospheric turbulence led to innovative designs like the 50-foot tower telescope at the McMath-Hulbert Observatory, operational from 1936, which elevated optics above ground-level seeing effects. Post-World War II developments included precursors to adaptive optics, such as early wavefront correction techniques tested on solar instruments in the 1950s and 1960s to compensate for air distortions. The era also saw the rise of vacuum tower telescopes, exemplified by the McMath-Pierce Solar Telescope dedicated in 1962, which evacuated the light path to eliminate internal air currents and improve image stability.^[24]^[25] In the late 20th century, solar telescopes grew in aperture size and fostered international collaborations, with the 50-cm Swedish Vacuum Solar Telescope commencing operations in 1972 at the Observatorio del Teide, later upgraded to a 1-m instrument in the early 2000s for enhanced resolution of solar dynamics. These advancements emphasized multi-wavelength observations and global data sharing, laying groundwork for modern solar research networks.^[26]

Design Principles

Optical Configurations

Solar telescopes employ a variety of optical configurations to capture and process the intense sunlight while minimizing distortions and thermal effects. Early designs predominantly utilized refracting telescopes with achromatic lenses, which consist of two or more elements—typically crown and flint glass—to correct for chromatic aberration by bringing different wavelengths to a common focus.^[27] These refractors were suitable for small to medium apertures, such as the 25-cm objective at the Udaipur Solar Observatory, enabling monochromatic observations like H-alpha imaging with minimal color fringing.^[27] However, modern solar telescopes favor reflecting configurations, particularly off-axis designs, to avoid central obstructions that cause diffraction spikes and to reduce heat buildup on the primary optic, as seen in the 4-m Daniel K. Inouye Solar Telescope (DKIST), where the off-axis Gregorian layout provides an unobstructed aperture and space for a heat-stop at prime focus.^[28] Focal arrangements in solar telescopes emphasize long effective focal lengths to achieve high angular resolution on the solar disk, with tower-based systems extending up to approximately 90 meters, as in the McMath-Pierce Solar Telescope, where a heliostat directs light down a vertical shaft to form a large image scale.^[29] This extended path enhances spatial resolution by magnifying solar features, producing images up to 333 mm in diameter for a 0.6-m aperture at f/60.^[27] The Coudé focus configuration is commonly employed to relocate instrumentation to a stable, heat-isolated laboratory environment away from the main optical train, as implemented in DKIST's transfer optics that route the f/13 Gregorian beam to a coudé room for multiple instruments.^[28] Beam directing systems track the Sun's motion to deliver a stable light path into the telescope. Heliostats use a single rotating flat mirror on an equatorial mount to reflect sunlight along a fixed polar axis, though this introduces image rotation at 15° per hour, often compensated by derotators like Dove prisms.^[27] Coelostats, by contrast, employ a fixed primary mirror and a rotating secondary on an alt-azimuth setup to produce a non-rotating horizontal beam, ideal for fixed spectrographs, as in the German Vacuum Tower Telescope.^[27] Specialized filters and polarimetric optics enable targeted observations of solar phenomena. Coronagraphs occult the bright solar disk to reveal the faint inner corona, typically using an external occulter and internal stops to suppress stray light, as in the Metis instrument on Solar Orbiter, which employs an inverted external occulter and a back-rejecting spherical mirror to image from 1.7 to 3.1 solar radii with reduced thermal load.^[30] Tunable Fabry-Pérot etalons provide narrowband filtering for spectral lines like H-alpha (656.3 nm), with bandpasses of tens to hundreds of milliangstroms adjusted via cavity spacing or tilt according to the relation m \lambda = 2 \mu d \cos \theta, allowing dynamic scanning of solar features.^[27] Vector magnetographs map solar magnetic fields by measuring Zeeman-induced polarization, using quarter-wave plates and analyzers in a collimated beam, as in the SVM-I at Udaipur Solar Observatory, which employs a piezo-scanned etalon and calcite polarizers to derive Stokes parameters across the 630 nm Fe I line.^[31] The theoretical resolution limit for these systems is governed by diffraction, given by \theta \approx 1.22 \lambda / D in radians, where \lambda is the wavelength and D the aperture diameter; converting to arcseconds yields \theta \approx 252,000 \lambda / D.^[27] For visible light at \lambda = 500 nm and a 4-m aperture like DKIST, this approaches 0.04 arcseconds, resolving features as small as 30 km on the Sun and underscoring the need for large apertures to overcome this fundamental limit.^[28]^[27]

Thermal and Seeing Management

Solar telescopes must manage intense thermal loads from concentrated sunlight, which can cause optical distortions through heating of components and induce internal seeing effects from convection currents. The primary heat load arises from solar irradiance, approximately 1 kW/m² at the Earth's surface, absorbed by the telescope's optics over its aperture area, with the absorbed power calculated as Q = I \cdot A \cdot (1 - R), where I is irradiance, A is the collecting area, and R is the reflectivity of the surface.^[32] This heat must be rejected efficiently to maintain structural stability and image quality, as even small temperature gradients can warp mirrors or create turbulent air flows within the instrument.^[33] Heat rejection strategies begin with a heat-stop positioned at the primary focus, which reflects over 95% of incoming solar radiation to prevent excessive absorption downstream, dissipating the remainder through radiative and convective cooling while keeping surface temperatures near ambient levels.^[33] For the primary mirror, active cooling systems circulate coolants such as water or synthetic fluids through embedded channels, maintaining temperature variations below 1°C to minimize thermal expansion and wavefront errors.^[17]^[34] Vacuum chambers or evacuated sections along the optical path further reduce convective heating by eliminating air-mediated heat transfer, a technique employed in early designs to suppress internal turbulence.^[35] These measures ensure that the telescope's optics remain thermally stable, with noncontact estimation methods verifying mirror temperatures in real time via heat transfer models.^[36] Atmospheric seeing, caused by turbulence in the air layers above the observatory, degrades resolution, but solar telescopes counteract this using adaptive optics (AO) systems that employ wavefront sensors to measure distortions and deformable mirrors to correct them in real time.^[37] Pioneered at facilities like the Dunn Solar Telescope, these systems achieve near-diffraction-limited imaging by compensating for the Sun's extended brightness as a natural guide source, unlike night-time astronomy's point stars.^[38] Multi-conjugate AO extends correction to multiple atmospheric layers using sequential deformable mirrors, widening the field of view and improving uniformity, as demonstrated at the New Solar Telescope.^[39]^[40] Site selection plays a critical role in minimizing seeing and thermal effects, favoring high-altitude locations with low water vapor content, such as Haleakalā in Hawaii or the Canary Islands, where reduced atmospheric thickness and stable boundary layers limit turbulence.^[41]^[42] Off-axis optical designs further mitigate ground-induced seeing by directing light paths away from heated telescope structures and surrounding terrain, avoiding convective plumes from the ground.^[43] Enclosures incorporate vent systems to promote airflow, flushing heated air and equalizing internal temperatures with the ambient environment during observations.^[44]^[45] Laser guide stars, while common in night-time AO, are impractical for solar applications due to the Sun's brightness overwhelming artificial beacons.^[46] Modern advancements integrate these elements for enhanced performance, with real-time AO processing enabling high-order corrections up to thousands of actuators, as seen in recent observations of fine coronal structures.^[47] Thermal modeling informs cooling requirements by simulating heat loads and airflow, ensuring designs like those for the European Solar Telescope handle up to 13 kW while preserving optical stability.^[48]

Types of Solar Telescopes

Professional Instruments

Professional solar telescopes are large-scale facilities designed for advanced heliophysics research, featuring apertures typically ranging from 1 to 4 meters to capture sufficient solar flux for high-resolution studies. These instruments are primarily funded by governmental and international bodies, such as the U.S. National Science Foundation (NSF) for facilities like the Daniel K. Inouye Solar Telescope (DKIST) and a multinational consortium of European countries, supported by EU programs including Horizon 2020 for preparatory phases and subsequent initiatives like Horizon Europe, for the planned 4-meter European Solar Telescope (EST). As of November 2025, the project has established a Board of Governmental Representatives to oversee construction, with first light expected around 2030.^[7]^[49] Such funding supports multi-wavelength observations spanning ultraviolet (starting at 380 nm), visible, and infrared (up to 2300 nm) regimes, enabling comprehensive analysis from the photosphere to the corona.^[7]^[48] Key instrumentation includes spectro-polarimeters, which measure Stokes parameters in spectral lines to derive Doppler velocities and magnetic field strengths in solar plasma with sub-arcsecond spatial resolution and spectral resolutions exceeding 100,000.^[50] Infrared detector arrays, such as HgCdTe or InSb sensors, are employed to probe cool features like sunspots, using lines like Fe I at 1565 nm to map magnetic fields up to 2500 G and reveal penumbral structures.^[51] Ultraviolet spectrometers focus on the transition region, capturing emissions from ions to study chromospheric dynamics, though ground-based access is limited and often supplemented by space missions.^[48] These telescopes operate in continuous daytime modes, with automated data pipelines processing high-cadence observations (e.g., multiple frames per second) to generate real-time products for space weather forecasting, including magnetograms and velocity maps.^[52] International collaborations, such as the Global Oscillation Network Group (GONG), provide 24/7 global coverage via six identical sites, achieving over 90% duty cycle for helioseismology and synoptic monitoring essential to space weather alerts.^[53] Facilities like the National Solar Observatory's Dunn Solar Telescope exemplify this, using its 0.76 m aperture in a vacuum tower to deliver high-resolution imaging and polarimetry of photospheric features.^[54] Integration with computational resources allows these instruments to support advanced simulations, correlating observational data with models of solar convection and magnetism.^[7] Since the early 2000s, emphasis has shifted to 4 m-class designs, enabling resolution of fine structures under 100 km on the solar surface—approximately three times finer than prior generations—for detailed studies of magnetic reconnection and turbulence.^[7] Many incorporate adaptive optics systems to mitigate atmospheric seeing, achieving near-diffraction-limited performance across broad fields of view.^[46]

Amateur Setups

Amateur astronomers can observe the Sun using compact, affordable equipment designed for safe and accessible solar viewing. Small refractor telescopes with apertures between 50mm and 150mm, equipped with full-aperture solar filters, are popular entry-level options for white-light observations of sunspots and the solar disk. These filters, such as Baader AstroSolar Safety Film with an optical density of 5.0, block 99.999% of incoming sunlight to prevent thermal damage to the instrument and ensure safe viewing. Hydrogen-alpha (H-alpha) telescopes, which isolate the 656.3 nm wavelength emitted by hydrogen in the solar chromosphere, offer views of prominences, filaments, and spicules; examples include the Coronado Personal Solar Telescope (PST), a 40mm aperture instrument with internal <1 Å bandpass filtering for portable H-alpha imaging. Safety is paramount in amateur solar observing, as direct exposure to unfiltered sunlight can cause permanent eye damage. Observers must never point unfiltered optics at the Sun and should use full-aperture solar filters from reputable manufacturers that meet safety guidelines for astronomical use, such as those with an optical density of at least 5.0 in the visible spectrum to block harmful UV and IR radiation, as recommended by the American Astronomical Society (AAS). These filters maintain color neutrality and durability against solar heat. Handheld solar viewers or eclipse glasses meeting ISO 12312-2:2015 criteria can supplement telescope use during events like partial eclipses.^[55]^[56] Basic observation techniques focus on visual and simple imaging of solar features. Visually, amateurs spot sunspots as dark umbrae with lighter penumbrae, dark filaments against the disk, and the mottled texture of photospheric granules on clear days. For imaging, webcams or modified digital cameras attached to the telescope capture short videos, which are then processed using stacking software like AutoStakkert! to align and combine frames, reducing noise and enhancing contrast for features like faculae or active regions. This method allows hobbyists to produce detailed images of the visible solar disk without advanced setups.^[57] Amateur solar setups are highly accessible, with costs ranging from $200 for basic refractors and filters to $2,000 for dedicated H-alpha systems like the Coronado PST or Lunt 50mm models. Community events, such as public solar eclipse viewings organized by astronomy clubs, provide hands-on opportunities, while mobile apps like SpaceWeatherLive deliver real-time forecasts of solar activity, including sunspot numbers and flare alerts, to optimize observing sessions. These tools enable participation from urban backyards or remote sites without specialized infrastructure.^[58]^[59] Limitations of amateur setups include reduced angular resolution compared to professional instruments, typically constrained by atmospheric seeing to about 1 arcsecond, versus 0.05 arcseconds achievable with adaptive optics in large observatories. Observations thus emphasize broad disk features like sunspot groups and limb prominences rather than fine chromospheric details.^[60]

Specialized Designs

Heliostat and Coelostat Systems

Heliostats are optical devices consisting of a single large flat mirror mounted on an equatorial drive that tracks the Sun's apparent motion across the sky, reflecting sunlight into a fixed telescope or instrument below. This design allows for compact solar telescope setups by directing the solar beam downward or horizontally without requiring an extended tube structure, thereby minimizing mechanical stress from long focal lengths. The mirror typically rotates at the solar rate, approximately equal to Earth's rotational speed of $15''/\mathrm{s}, to maintain alignment with the Sun.^[27]^[61] Coelostats, in contrast, employ a two-mirror system to produce a stationary image of the Sun, with a primary flat mirror mounted parallel to Earth's polar axis and rotating at half the solar rate—also derived from the $15''/\mathrm{s} equatorial tracking rate—to compensate for diurnal motion, while a fixed or slowly adjusting secondary mirror directs the beam to the instrument. Invented by French physicist Gabriel Lippmann in 1895, this configuration eliminates image rotation inherent in single-mirror systems, facilitating stable attachment of heavy instrumentation like spectrographs or polarimeters directly to a fixed focal plane.^[62]^[27]^[61] Both systems offer key advantages in solar astronomy, including reduced mechanical complexity compared to fully rotating large telescopes and the ability to feed a single collected beam to multiple instruments simultaneously, such as in polarimetry setups where stable pointing is essential. For instance, the McMath-Pierce Solar Telescope at Kitt Peak National Observatory employs a heliostat atop its tower to direct sunlight down a vacuum shaft for high-resolution observations. Coelostats are particularly valued for long-exposure studies, as seen in the German Vacuum Tower Telescope (VTT) on Tenerife, where the system supports two-dimensional spectropolarimetry with polarization efficiencies exceeding 50% at 630 nm and spatial resolutions better than 0.5 arcsec when paired with adaptive optics. Historically, these devices have enabled precise solar imaging since the late 19th century, evolving to integrate with tower structures for elevated, seeing-minimized paths.^[25]^[63]^[27] Despite their benefits, heliostats and coelostats require stringent mirror alignment to prevent image wander, with tracking accuracies typically better than 0.1 arcsec over short intervals to avoid degrading resolution in fine-scale solar features. Heliostats suffer from field rotation at 15° per hour, necessitating derotators like Dove prisms for extended observations, while coelostats demand precise synchronization of the two mirrors to mitigate time-varying incidence angles that could introduce polarization artifacts in modern applications.^[27]^[64]^[63]

Tower Telescopes

Tower telescopes employ vertical architectural designs that elevate the optical path high above the ground to mitigate atmospheric seeing effects. These structures typically consist of tall towers, typically 30 to 50 meters in height, such as the McMath-Pierce Solar Telescope's 30.5-meter heliostat tower combined with an extensive underground shaft for a total light path exceeding 150 meters. Sunlight is captured by a heliostat at the tower's apex and directed horizontally into an evacuated tube that extends downward, housing the primary optics at the base. This elevation positions the light path above the turbulent atmospheric boundary layer near the surface, significantly reducing wavefront distortions from ground-heated air convection.^[65]^[66]^[67] The design facilitates exceptionally long effective focal lengths, often between 50 and 200 meters, which support magnifications up to several thousand times for high-resolution imaging. For instance, the 60-foot Snow Solar Telescope, completed in 1908 at Mount Wilson Observatory, achieves an 18-meter focal length to enable detailed spectroheliograph observations. The evacuated enclosure of the light path prevents internal air currents and thermal gradients that could induce refractive index variations, thereby preserving image sharpness by eliminating convection-induced turbulence.^[65]^[23]^[68] Contemporary implementations incorporate advanced features like adaptive optics to compensate for residual atmospheric aberrations. The New Solar Telescope at Big Bear Solar Observatory exemplifies this hybrid approach, with its 83-meter effective focal length and integrated AO system for real-time wavefront correction. These towers deliver superior spatial resolution, on the order of 0.1 arcseconds or better, crucial for investigating solar granulation patterns and convective dynamics. Despite these advantages, the elevated frameworks face engineering hurdles, including heightened vulnerability to wind-induced vibrations and substantial construction expenses for reinforced supports and vacuum maintenance.^[65]^[69]^[70]

Notable Facilities

Historical Examples

The Snow Solar Telescope, relocated to Mount Wilson Observatory in 1904 by George Ellery Hale, was one of the earliest dedicated solar instruments. This horizontal telescope, using a coelostat to direct sunlight, enabled initial high-resolution studies of sunspots and solar spectra, marking the beginning of systematic solar observation at altitude to reduce atmospheric distortion.^[9] The 60-Foot Solar Tower at Mount Wilson, completed in 1908, introduced a vertical configuration with a heliostat atop a 60-foot (18-meter) tower. This design improved image stability by placing optics above turbulent boundary layers, facilitating spectroscopic observations that advanced understanding of solar magnetic fields.^[10] The 150-foot Tower Solar Telescope at Mount Wilson Observatory, operational since 1912 and later upgraded in the 1960s with enhanced spectrograph capabilities, stood as a cornerstone for long-term solar monitoring. Its vertical design and heliostat system provided stable, high-resolution views, where early helioseismology experiments in the 1960s detected oscillations in the Sun's surface, linking them to internal dynamics. It also documented variations across the 11-year solar cycle, contributing to models of solar activity prediction. The McMath-Pierce Solar Telescope, dedicated in 1962 at Kitt Peak National Observatory with a 1.6-meter entrance aperture, represented a significant leap in solar instrumentation due to its unprecedented 87-meter focal length achieved through a series of mirrors.^[71] This design minimized atmospheric distortion and allowed for high-dispersion spectroscopy, pioneering infrared observations of the solar spectrum that revealed new absorption lines and temperature profiles. Throughout the mid-20th century, it facilitated key studies on solar granulation and limb darkening, influencing subsequent telescope designs. The Richard B. Dunn Solar Telescope at Sacramento Peak Observatory, featuring a 76 cm (0.76-meter) aperture and a 65-meter evacuated tower commissioned in 1970, advanced vacuum tower technology to suppress thermal turbulence. Building on the observatory's origins in 1947 for solar flare monitoring during and after World War II, it enabled precise imaging of solar flares correlated with radio bursts in systematic observations, improving understanding of solar activity's impact on Earth's ionosphere and radio communications. By the early 2000s, many 20th-century solar towers, including the McMath-Pierce facility decommissioned in 2018, faced decommissioning due to advancements in adaptive optics and digital imaging that rendered older vacuum and long-focal-length systems less efficient for modern research demands. This shift allowed resources to be redirected toward more versatile ground- and space-based observatories.

Modern and Future Telescopes

The Daniel K. Inouye Solar Telescope (DKIST), located on Haleakalā in Maui, Hawaii, represents the pinnacle of contemporary ground-based solar observation facilities, achieving first light in 2019 with a 4-meter off-axis Gregorian primary mirror that collects more sunlight than any other solar telescope.^[7] This design minimizes scattered light and thermal distortion, enabling unprecedented views of solar features down to approximately 0.03 arcseconds in resolution when paired with advanced adaptive optics systems.^[72] DKIST's suite of instruments, including spectro-polarimeters and narrowband imagers, facilitates detailed studies of magnetic reconnection processes in the solar atmosphere, contributing to improved models of solar eruptions and space weather impacts.^[73] In the Canary Islands, the GREGOR telescope, operational since 2012 at the Teide Observatory in Tenerife, features a 1.5-meter aperture optimized for high-resolution imaging and spectro-polarimetry in visible and near-infrared wavelengths.^[74] Its open-air Gregorian configuration, supported by adaptive optics, allows for efficient air flushing to reduce seeing effects, while fiber-fed spectrographs like GRIS enable precise measurements of chromospheric dynamics, such as wave propagation and magnetic field evolution.^[75] Funded through European Union collaborations involving German and Spanish institutions, GREGOR has advanced understanding of solar convection and oscillations through its versatile post-focus instrumentation.^[76] The Swedish 1-m Solar Telescope (SST), situated at the Roque de los Muchachos Observatory on La Palma since 2003, exemplifies refined vacuum-lens technology for diffraction-limited performance, upgraded in 2010 with multi-conjugate adaptive optics to achieve resolutions approaching 0.1 arcseconds.^[77] This facility excels in high-cadence imaging of atmospheric waves and magnetic structures using instruments like CRISP and CHROMIS, which provide spectropolarimetric data across multiple wavelengths.^[78] SST's commitment to an open data policy, with public archives of processed observations, has fostered collaborative research on solar magnetism and dynamic phenomena.^[79] Looking ahead, the European Solar Telescope (EST), a 4-meter class instrument planned for the Roque de los Muchachos Observatory with first light targeted for 2027, will incorporate multi-conjugate adaptive optics to deliver sub-arcsecond resolution across the solar atmosphere.^[80] Its design supports up to eight simultaneous instruments, including polarimeters and spectrographs, focused on tracing magnetic connectivity from the photosphere to the corona.^[48] Construction preparations advanced in 2023 with the establishment of an international foundation, building on preparatory phases initiated in 2021 to ensure integration of cutting-edge diagnostics for solar plasma physics.^[81] Emerging trends in solar telescopy emphasize the fusion of artificial intelligence with observational data to handle the vast volumes generated by these facilities, as seen in deep learning models applied to DKIST datasets for real-time atmospheric visualization and property estimation.^[82] Global networks, such as the NSF-funded Global Oscillation Network Group (GONG) with its six synchronized stations, enable continuous 24-hour monitoring of solar oscillations and activity, complemented by proposed expansions like the NSO's next-generation worldwide array.^[53] Aperture sizes exceeding 4 meters, as in DKIST and EST, are driving capabilities toward sub-arcsecond views of the low corona, enhancing studies of faint emissions and magnetic fields through increased light-gathering power and advanced wavefront correction.^[83]

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Optical design of the multi-wavelength imaging coronagraph Metis ...
May 20, 2020 · This paper describes the innovative optical design of the Metis coronagraph for the Solar Orbiter ESA-NASA mission.
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[PDF] Design and Status of Solar Vector Magnetograph (SVM-I) at Udaipur ...
SVM-I is an instrument which aims to determine the mag- netic field vector in the solar atmosphere by measuring Zeeman induced polarization across the spectral ...
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Thermal characteristics of a classical solar telescope primary mirror
Feb 1, 2011 · We present a detailed thermal and structural analysis of a 2m class solar telescope mirror which is subjected to a varying heat load at an ...<|separator|>
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Modeling and experiment validation of thermal control for the heat ...
Aug 6, 2021 · Heat-stop is one of the key components for controlling thermal effects for a large solar telescope, which reflects over 95% of solar radiation ...
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Active thermal control for the 1.8-m primary mirror of the solar ...
Aug 9, 2025 · The optical performance and pointing accuracy of the 1.5 m solar telescope GREGOR depend on the passive and active temperature control design ...<|separator|>
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Cooling air flow field in the primary mirror temperature control ...
We designed a flow field structure of the primary mirror temperature control system based on the 2.5-meter Wide-field and High-resolution Solar Telescope(WeHoT ...Missing: management | Show results with:management
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Noncontact temperature estimation method on the actively cooled ...
Nov 2, 2017 · A noncontact temperature estimation method based on the analytical heat transfer model of actively cooled primary mirror of a solar telescope is ...
[36]
Adaptive Optics - The Challenge of the Atmosphere for the Inouye ...
Solar adaptive optics was pioneered at NSO's former telescope – the Dunn Solar Telescope – by the Director of the Inouye Solar Telescope himself, Dr. Thomas ...
[37]
Solar Adaptive Optics - PMC - NIH
Solar AO systems enable diffraction limited observations of the Sun for a significant fraction of the available observing time at ground-based solar telescopes, ...
[38]
Next generation of adaptive optics widens the field for observations ...
The Multi-Conjugate Adaptive Optics system at the New Solar Telescope of the Big Bear Solar Observatory uses three sequential deformable mirrors, changing shape ...
[39]
Clear widens the field for observations of the Sun with multi ...
The multi-conjugate adaptive optics (MCAO) pathfinder Clear on the New Solar Telescope in Big Bear Lake has provided the first-ever MCAO-corrected observations ...<|separator|>
[40]
Three Sites Selected as Candidates for World's Largest Solar ...
The National Solar Observatory narrows location selection to three sites for world's largest ground-based solar telescope.
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Large Solar Telescopes - Big Bear Solar Observatory
Apr 24, 2019 · Swedish VTT (Vacuum Tower Telescope, replaced by SST), rT, 50cm, 1985 ... T = tower (generally a fixed telescope with a heliostat, coelostat, or ...
[42]
[PDF] First Light of the 1.6 meter off-axis New Solar Telescope at Big Bear ...
In contrast with most solar telescopes in operation which have on-axis configurations, the NST adopts a unique off-axis optical design. Since the Secondary ...
[43]
Enclosure - NSO - National Solar Observatory
The Enclosure is the large structure that surrounds and provides protection for the Telescope Assembly. It includes a variety of mechanical subassemblies, ...Missing: vents airflow
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Enclosure - European Solar Telescope
The enclosure safeguards the telescope, maintains temperature, is a retractable dome, shields from adverse conditions, and has ventilation and sealing systems.
[45]
Solar Adaptive Optics | Living Reviews in Solar Physics
Laser guide stars are not a practical solution for solar AO since either extremely bright lasers would be needed to project a laser spot against the bright ...<|separator|>
[46]
Observations of fine coronal structures with high-order solar ... - Nature
May 27, 2025 · Adaptive optics systems have been used for over two decades to reach the diffraction limit of large telescopes, thereby compensating for ...
[47]
The European Solar Telescope | Astronomy & Astrophysics (A&A)
The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper ...
[48]
Instrumentation for solar spectropolarimetry: state of the art and ...
In this review, we focus on instrumental technology and techniques employed by the solar community to satisfy the demand for data with increasing polarimetric ...
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Infrared Solar Physics - PMC - PubMed Central - NIH
The infrared solar spectrum contains a wealth of physical data about our Sun, and is explored using modern detectors and technology with new ground-based solar ...
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Continuous Solar Observations from the Ground—Assessing Duty ...
Oct 5, 2021 · We assess the duty cycle that has been achieved from the ground by analyzing the observations of a six station network of identical instruments.
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Global Oscillations Network Group - NSO - National Solar Observatory
The Global Oscillation Network Group, or GONG Network is a worldwide network of six identical telescopes, designed to have 24/7 observations of the Sun.
[52]
Continuing Operations at the Dunn Solar Telescope | Solar Physics
Jul 22, 2025 · The instrumentation at the DST continues to provide high cadence imaging, spectroscopy, and polarimetry of the solar photosphere and ...
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About the ISO 12312-2 Standard for Solar Viewers
ISO 12312-2 specifies the properties that a solar viewer should have in order to protect your eyes from injury and provide a comfortable view.
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ISO 12312-2:2015 - Eye and face protection
In stock 2–5 day deliveryISO 12312-2:2015 applies to all afocal (plano power) products intended for direct observation of the sun, such as solar eclipse viewing.
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AutoStakkert! – AutoStakkert!4 Stacking Software – Lucky Imaging ...
AutoStakkert! (AS!3, AS!2) is lucky imaging software used to automatically analyze, align, and stack images of the Sun, Moon and Planets that were taken ...Download · Features and Guides · Page 2 – AutoStakkert!4... · Enhance!
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Solar Telescopes, Solar Filters & Accessories - High Point Scientific
The film used in solar eclipse glasses needs to meet the ISO 12312-2 standard to provide a safe viewing experience. There are a wide range of ...
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SpaceWeatherLive app
SpaceWeatherLive is the ultimate app for those who are interested in seeing the northern lights or want to know everything about the activity on our Sun.
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Telescope resolution
Resolution is another vital telescope function. Simply put, telescope resolution limit determines how small a detail can be resolved in the image it forms.
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Coelostat and heliostat - Theory of alignment - NASA ADS
For perfectly aligned heliostats and coelostats tracking at the solar rate and half the solar rate, respectively, the solar beam has no translational motion.
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Gabriel Lippmann – Biographical - NobelPrize.org
He contributed to astronomy with his invention of the coelostat, a device which immobilizes the image of a star and its surrounding stars so that a photograph ...
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Two-dimensional solar spectropolarimetry with the KIS/IAA Visible ...
The instrumental polarization caused by the VTT coelostat is removed using the telescope model of Beck et al. (2005a). If the polarization level in a ...<|control11|><|separator|>
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[PDF] Multi Application Solar Telescope (MAST)
Tracking accuracy: 0.1 arc-sec in 10 s; 0.5 arc-sec in 600 s. 4. Slew rate/ fast movement rate: 2° per sec available for Mt. Abu telescope but small.
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Solar telescopes - Scholarpedia
Apr 16, 2008 · Introduction. Solar telescopes are based on the same construction ... Coelostat system. The SST is a refractor, with a 1-m lens that ...<|control11|><|separator|>
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McMath-Pierce Solar Telescope - SOM
The McMath-Pierce Solar Telescope on Arizona's Kitt Peak was the world's largest instrument dedicated to viewing the sun at the time of its completion.Missing: history 1935
[65]
High resolution solar telescopes - NASA ADS
... Vacuum Tower Telescope at Sac Peak (Dunn, 1964, 1969). This altazimuth ... A similar design, but with an outer tower for a windscreen, was proposed for ...
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An Evacuated Tower Telescope - Optica Publishing Group
The design features a simple optical system, complete control over the motion of the image, and an evacuated interior to reduce internal turbulence and permit ...
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New Telescope - Big Bear Solar Observatory
Apr 7, 2008 · The BBSO NST (New Solar Telescope) replaces the old telescope assembly (65-cm vacuum telescope, 25-cm vacuum telescope, 20-cm full-disk telescope) at BBSO.Missing: tower | Show results with:tower
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High resolution 2D-spectroscopy of granular dynamics
Spectroscopic data with high spatial resolution are used to study the granular dynamics of the Sun.
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Follow the Photons through the Inouye Solar Telescope - NSO
Ten mirrors guide the sunlight throughout the Inouye Solar Telescope, each playing a vital role in delivering the sharpest images of our Sun.<|control11|><|separator|>
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Daniel K. Inouye Solar Telescope starts year-long science ... - NSF
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GREGOR Solar Telescope | Instituto de Astrofísica de Canarias • IAC
GREGOR is the largest solar telescope in Europe. It is designed for observations of the solar photosphere and chromosphere in the visible and near infrared.
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[PDF] The 1.5 meter solar telescope GREGOR
Nov 2, 2012 · ... Vacuum Tower Telescope. GREGOR is Europe's largest solar telescope and number 3 in the world. Its all-reflective Gregory design provides a ...
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GREGOR first results | Astronomy & Astrophysics (A&A)
With an aperture of 1.5 m, the new solar telescope GREGOR operating in Tenerife is the largest of its kind in Europe. It provides an unprecedented ...
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The telescope - Institute for Solar Physics
Feb 6, 2023 · The Swedish 1-m Solar Telescope (SST) on the island of La Palma, Spain, had first light with a stopped down 60 cm aperture on March 2, 2002.Missing: history 1971
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Swedish Solar Telescope | Instituto de Astrofísica de Canarias • IAC
Following extensive site testing, the Royal Swedish Academy of Sciences established its solar observatory at the Roque de los Muchachos. Our first major solar ...Missing: 1971 | Show results with:1971
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https://www.aanda.org/articles/aa/full_html/2016/12/aa30019-16/aa30019-16.html
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EST - European Solar Telescope
The European Solar Telescope (EST) is a next generation large-aperture solar telescope. This 4-metre telescope will be optimised for studies of the magnetic ...
[78]
The European Solar Telescope project presents the design for its ...
Sep 29, 2022 · It is planned to start construction in 2024, in the Roque de los Muchachos Observatory (La Palma, Canary Islands).
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AI and Astronomy: UH researchers to help decode Sun's secrets
Feb 14, 2025 · UH researchers use deep learning models to analyze solar telescope data, estimate solar properties, and visualize the Sun's atmosphere in real- ...
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EST Project - European Solar Telescope
The European Solar Telescope (EST) is a next generation large-aperture solar telescope. This 4-metre telescope will be optimised for studies of the magnetic ...