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40-531: The McMath-Hulbert Solar Observatory is a solar observatory in Lake Angelus, Michigan , USA. It was established in 1929 as a private observatory by father and son Francis Charles McMath and Robert Raynolds McMath and their friend, Judge Henry Hulbert . In 1932 the observatory was deeded to the University of Michigan which operated it until 1981, at which time it was sold into private ownership again. In 1932

80-550: A 10.5-inch (270 mm) reflector telescope was added to the observatory as well as a spectroheliokinematograph { spectro-helio-kine-mato-graph }. This instrument was designed to take motion pictures of the Sun. The McMath-Hulbert Solar Observatory is primarily known for the motion pictures that the McMaths made of various celestial phenomena, including the first movies of solar prominences in motion. Later work involved solar spectroscopy in

120-470: 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

160-425: 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 or helium to eliminate air motion due to convection inside the telescope. However, this

200-424: A large paraboloidal reflector which brings them to a precise focus. The mirrors have to be located close enough to the axis of the paraboloid to reflect sunlight into it along lines parallel to the axis, so the field of heliostats has to be narrow. A closed loop control system is used. Sensors determine if any of the heliostats is slightly misaligned. If so, they send signals to correct it. It has been proposed that

240-455: A single collector to heat a medium such as water or molten salt. The medium travels through a heat exchanger to heat water, produce steam, and then generate electricity through a steam turbine. A somewhat different arrangement of heliostats in a field is used at experimental solar furnaces, such as the one at Odeillo , in France. All the heliostat mirrors send accurately parallel beams of light into

280-406: A solar power tower system. Instead of occupying hundreds of acres, the system would fit in a much smaller area, like the flat rooftop of a commercial building, he said. The proposed system would use the power in sunlight to heat and cool a building or to provide input for thermal industrial processes like processing food. The cooling would be performed with an absorption chiller . Rohr proposed that

320-400: Is a device that includes a mirror, usually a plane mirror , which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the Sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space. To do this, the reflective surface of the mirror is kept perpendicular to the bisector of the angle between

360-498: 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 , with peak powers of 11.4 kW. The goal of such

400-452: Is for the mirror to rotate around a polar aligned primary axis, driven by a mechanical, often clockwork, mechanism at 15 degrees per hour, compensating for the Earth's rotation relative to the Sun. The mirror is aligned to reflect sunlight along the same polar axis in the direction of one of the celestial poles . There is a perpendicular secondary axis allowing occasional manual adjustment of

440-444: Is given the latitude and longitude of the heliostat's position on the Earth and the time and date. From these, using astronomical theory, it calculates the direction of the Sun as seen from the mirror, e.g. its compass bearing and angle of elevation. Then, given the direction of the target, the computer calculates the direction of the required angle-bisector, and sends control signals to motors , often stepper motors , so they turn

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480-632: Is in the Science Museum Group collection. Currently, most heliostats are used for daylighting or for the production of concentrated solar power , usually to generate electricity. They are also sometimes used in solar cooking . A few are used experimentally to reflect motionless beams of sunlight into solar telescopes . Before the availability of lasers and other electric lights, heliostats were widely used to produce intense, stationary beams of light for scientific and other purposes. Most modern heliostats are controlled by computers. The computer

520-503: 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 Sun's narrow path across the sky, some solar telescopes are fixed in position (and are sometimes buried underground), with

560-409: Is often referred to as a glass/metal heliostat. Alternative designs incorporate recent adhesive, composite, and thin film research to bring about materials costs and weight reduction. Some examples of alternative reflector designs are silvered polymer reflectors, glass fiber reinforced polyester sandwiches (GFRPS), and aluminized reflectors. Problems with these more recent designs include delamination of

600-431: Is the target-axis arrangement in which the primary axis points toward the target at which sunlight is to be reflected. The secondary axis is perpendicular to the primary one. Heliostats controlled by light-sensors have used this orientation. A small arm carries sensors that control motors that turn the arm around the two axes, so it points toward the sun, incorporating a solar tracker. A simple mechanical arrangement bisects

640-402: The chromosphere . Specialized solar telescopes facilitate clear observation of such H-alpha emissions by using a bandwidth filter implemented with a Fabry-Perot etalon . A solar tower is a structure used to support equipment for studying the Sun, and is typically part of solar telescope designs. Solar tower observatories are also called vacuum tower telescopes. Solar towers are used to raise

680-549: The near infrared and participation in a solar flare patrol program in the 1950s. Robert McMath and one of the resident astronomers, Keith Pierce , established the McMath–Pierce solar telescope at Kitt Peak Observatory near Tucson, Arizona in 1962. The McMath-Hulbert Solar Observatory is currently under private ownership but is run by a small non-for-profit organization of amateur astronomers. Solar observatory Solar telescopes need optics large enough to achieve

720-527: The Earth's surface due to the absorption of the atmosphere: 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 , Herschel wedges 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

760-617: The Solar Tower Atmospheric Cherenkov Effect Experiment ( STACEE ), which is being used to study Cherenkov radiation , and the Weizmann Institute solar power tower . Other solar telescopes that have solar towers are Richard B. Dunn Solar Telescope , Solar Observatory Tower Meudon and others. Heliostat A heliostat (from helios , the Greek word for sun , and stat , as in stationary)

800-484: The angle between the primary axis, pointing to the target, and the arm, pointing to the Sun. The mirror is mounted so its reflective surface is perpendicular to this bisector. This type of heliostat was used for daylighting prior to the availability of cheap computers, but after the initial availability of sensor control hardware. There are heliostat designs which do not require the rotation axes to have any exact orientation. For example, there may be light-sensors close to

840-404: The best possible diffraction limit but less so for the associated light-collecting power of other astronomical telescopes. However, recently newer narrower filters 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

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880-449: The costs of heliostats is by replacing the conventional heliostat design with one that uses fewer, lighter materials. A conventional design for the heliostat's reflective components utilizes a second surface mirror. The sandwich-like mirror structure generally consists of a steel structural support, an adhesive layer, a protective copper layer, a layer of reflective silver, and a top protective layer of thick glass. This conventional heliostat

920-472: The directions of the Sun and the target as seen from the mirror. In almost every case, the target is stationary relative to the heliostat, so the light is reflected in a fixed direction. According to contemporary sources the heliostata, as it was called at first, was invented by Willem 's Gravesande (1688–1742). Other contenders are Giovanni Alfonso Borelli (1608–1679) and Daniel Gabriel Fahrenheit (1686–1736). A heliostat designed by George Johnstone Storey

960-527: The ground or on a building structure like a roof, moves on two axes (up/down and left/right) in order to compensate for the constant movement of the Sun. In this way, the reflected sunlight stays fixed on the target (e.g. window). Genzyme Center, corporate headquarters of Genzyme Corp. in Cambridge, Massachusetts, uses heliostats on the roof to direct sunlight into its12-story atrium. In a 2009 article, Bruce Rohr suggested that small heliostats could be used like

1000-404: The heliostat mirror moves at a rate that is 1/2 the angular motion of the Sun. There is another arrangement that satisfies the definition of a heliostat yet has a mirror motion that is 2/3rd of the motion of the Sun. Many other types of heliostat have also occasionally been used. In the very earliest heliostats, for example, which were used for daylighting in ancient Egypt, servants or slaves kept

1040-444: The high temperatures generated could be used to split water producing hydrogen sustainably. Smaller heliostats are used for daylighting and heating. Instead of many large heliostats focusing on a single target to concentrate solar power (as in a solar power tower plant), a single heliostat usually about 1 or 2 square meters in size reflects non-concentrated sunlight through a window or skylight. A small heliostat, installed outside on

1080-476: The location country. It is of interest to design less expensive heliostats for large-scale manufacturing, so that solar power tower power plants may produce electricity at costs more competitive to conventional coal or nuclear power plants costs. Besides cost, percent solar reflectivity (i.e. albedo ) and environmental durability are factors that should be considered when comparing heliostat designs. One way that engineers and researchers are attempting to lower

1120-466: The mirror (daily or less often as necessary) to compensate for the shift in the Sun's declination with the seasons. The setting of the drive clock can also be occasionally adjusted to compensate for changes in the Equation of Time . The target can be located on the same polar axis that is the mirror's primary rotation axis, or a second, stationary mirror can be used to reflect light from the polar axis toward

1160-622: The mirror to the correct alignment. This sequence of operations is repeated frequently to keep the mirror properly oriented. Large installations such as solar-thermal power stations include fields of heliostats comprising many mirrors. Usually, all the mirrors in such a field are controlled by a single computer. There are older types of heliostat which do not use computers, including ones that are partly or wholly operated by hand or by clockwork , or are controlled by light- sensors . These are now quite rare. Heliostats should be distinguished from solar trackers or sun-trackers that point directly at

1200-467: The mirrors aligned manually, without using any kind of mechanism. (There are places in Egypt where this is done today, for the benefit of tourists. In the 1997 film The Fifth Element an Egyptian boy holds a mirror to illuminate a wall inside a cave for a fictional archaeologist.) Elaborate clockwork heliostats were made during the 19th Century which could reflect sunlight to a target in any direction using only

1240-422: The observation equipment above atmospheric turbulence caused by solar heating of the ground and the radiation of the heat into the atmosphere. Traditional observatories do not have to be placed high above ground level, as they do most of their observation at night, when ground radiation is at a minimum. The horizontal Snow solar observatory was built on Mount Wilson in 1904. It was soon found that heat radiation

McMath–Hulbert Observatory - Misplaced Pages Continue

1280-835: The only moving part being a heliostat to track the Sun. One example of this is the McMath-Pierce Solar Telescope . The Sun, being the closest star to earth, allows a unique chance to study stellar physics with high-resolution. It was, until the 1990s, the only star whose surface had been resolved. General topics that interest a solar astronomer are its 11-year periodicity (i.e., the Solar Cycle ), sunspots , magnetic field activity (see solar dynamo ), solar flares , coronal mass ejections , differential rotation , and plasma physics . Most solar observatories observe optically at visible, UV, and near infrared wavelengths, but other solar phenomena can be observed — albeit not from

1320-424: The protective coatings, reduction in percent solar reflectivity over long periods of sun exposure, and high manufacturing costs. The movement of most modern heliostats employs a two-axis motorized system, controlled by computer as outlined at the start of this article. Almost always, the primary rotation axis is vertical and the secondary horizontal, so the mirror is on an alt-azimuth mount . One simple alternative

1360-415: The reflected beam, when it reappears, misses the sensors, so the system cannot correct the orientation of the mirror. There are also geometrical problems which limit the functioning of the heliostat when the directions of the Sun and the target, as seen from the mirror, are very different. Because of the disadvantages, this design has never been commonly used, but some people do experiment with it. Typically,

1400-409: 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

1440-513: The sun in the sky. However, some older types of heliostat incorporate solar trackers, together with additional components to bisect the sun-mirror-target angle. A siderostat is a similar device which is designed to follow a fainter star , rather than the Sun. In a solar-thermal power plant, like those of The Solar Project or the PS10 plant in Spain, a wide field of heliostats focuses the Sun's power onto

1480-421: The system would be "more reliable and more cost-effective per square meter of reflective area" than large solar power tower plants, in part because it would not be sacrificing 80 percent of the power collected in the process of converting it to electricity. Heliostat costs represent 30-50% of the initial capital investment for solar power tower power plants depending on the energy policy and economic framework in

1520-411: The target which send signals to motors so that they correct the alignment of the mirror whenever the beam of reflected light drifts away from the target. The directions of the axes need be only approximately known, since the system is intrinsically self-correcting. However, there are disadvantages, such as that the mirror has to be manually realigned every morning and after any prolonged cloudy spell, since

1560-421: The target, wherever that might be. This kind of mirror mount and drive is often used with solar cookers , such as Scheffler reflectors . For this application, the mirror can be concave , so as to concentrate sunlight onto the cooking vessel. The alt-azimuth and polar-axis alignments are two of the three orientations for two-axis mounts that are, or have been, commonly used for heliostat mirrors. The third

1600-537: Was disrupting observations. Almost as soon as the Snow Observatory opened, plans were started for a 60-foot-tall (18 m) tower that opened in 1908 followed by a 150-foot (46 m) tower in 1912. The 60-foot tower is currently used to study helioseismology , while the 150-foot tower is active in UCLA 's Solar Cycle Program. The term has also been used to refer to other structures used for experimental purposes, such as

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