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58-452: This telescope is notable for the discovery that sunspots have a lower temperature than the photosphere , and for finding evidence they are associated with a magnetic field . During his time at Yerkes Observatory , American solar astronomer George Ellery Hale developed a horizontal telescope for observation of the Sun. This instrument used a 30-inch (76 cm) diameter coelostat to track

116-895: A star catalogue . By 28 BC, Chinese astronomers were regularly recording sunspot observations in official imperial records. The first clear mention of a sunspot in Western literature is circa 300 BC, by ancient Greek scholar Theophrastus , student of Plato and Aristotle and successor to the latter. The earliest known drawings of sunspots were made by English monk John of Worcester in December 1128. Sunspots were first observed telescopically in December 1610 by English astronomer Thomas Harriot . His observations were recorded in his notebooks and were followed in March 1611 by observations and reports by Frisian astronomers Johannes and David Fabricius . After Johannes Fabricius' death at

174-443: A Bushfire Attack Level category greater than BAL-Low. Often used interchangeably by mistake, the key difference between louvers and jalousies is that louvers are fixed position. Jalousies are installed within a movable adjustable mechanism which positions all jalousies into any parallel position with respect to each other. Louvers are rarely seen as primary design elements in the language of modern architecture , but rather simply

232-450: A brighter region known as the penumbra. The penumbra is composed of radially elongated structures known as penumbral filaments and has a more inclined magnetic field than the umbra. Within sunspot groups, multiple umbrae may be surrounded by a single, continuous penumbra. The temperature of the umbra is roughly 3000–4500 K, in contrast to the surrounding material at about 5780 K, leaving sunspots clearly visible as dark spots. This

290-487: A connection between wheat prices and sunspots, and modern analysis finds that there is no statistically significant correlation between wheat prices and sunspot numbers. Sunspots have two main structures: a central umbra and a surrounding penumbra . The umbra is the darkest region of a sunspot and is where the magnetic field is strongest and approximately vertical, or normal , to the Sun's surface, or photosphere . The umbra may be surrounded completely or only partially by

348-401: A few hundred meters per second when they first emerge. Indicating intense magnetic activity, sunspots accompany other active region phenomena such as coronal loops , prominences , and reconnection events. Most solar flares and coronal mass ejections originate in these magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on stars other than

406-431: A matter of ongoing research, it is widely understood that they are the visible manifestations of magnetic flux tubes in the Sun's convective zone projecting through the photosphere within active regions. Their characteristic darkening occurs due to this strong magnetic field inhibiting convection in the photosphere. As a result, the energy flux from the Sun's interior decreases, and with it, surface temperature, causing

464-549: A moving telescope. Hale's coelostat was housed on the south side of the Yerkes Observatory in a canvas-covered structure. Unfortunately, shortly after this instrument was made ready, the housing was destroyed by an electrical fire during December 1902. Most of the telescope was ruined as a result, including the coelostat mirror and a specially ruled diffraction grating . Thanks to a donation of $ 10,000 by Helen E. Snow of Chicago (equivalent to $ 339,111 in 2023),

522-504: A penumbra will begin to form. Magnetic pressure should tend to remove field concentrations, causing the sunspots to disperse, but sunspot lifetimes are measured in days to weeks. In 2001, observations from the Solar and Heliospheric Observatory (SOHO) using sound waves traveling below the photosphere (local helioseismology ) were used to develop a three-dimensional image of the internal structure below sunspots; these observations show that

580-454: A powerful downdraft lies beneath each sunspot, forms a rotating vortex that sustains the concentrated magnetic field. Solar cycles last typically about eleven years, varying from just under 10 to just over 12 years. Over the solar cycle, sunspot populations increase quickly and then decrease more slowly. The point of highest sunspot activity during a cycle is known as solar maximum, and the point of lowest activity as solar minimum. This period

638-505: A staple in the design of homes and perfect to withstand the pressures of future cyclonic conditions. Cyclone homes have always been synonymous with louver windows, louver blades have been tested for ‘debris type B’ for cyclonic regions. Rear window louvers are also available as an accessory for some automobiles. They have also been used over the years in hoods, trunk lids, and other various body panels; typically hot rods , but by no means exclusive to that period. Their purpose in this regard

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696-674: A technical device. Louvers are part of the design of Demerara windows to help keep 18th and 19th century buildings cool in hot climates and block direct sunlight. Some modern louver systems serve to improve indoor daylighting . Fixed mirrored louver systems can limit glare and of redirect diffuse light. Such louvers may be integrated in between two panes of double glazing . In industrial facilities such as steel foundries and power plants , louvers are very common. They are utilized for natural ventilation and temperature control. Louvers are frequently found in bell towers , where they are utilised to let out as much sound as possible, while having

754-405: A weaker, more tilted magnetic field compared to the umbra at the same height in the photosphere. Higher in the photosphere, the light bridge magnetic field merges and becomes comparable to that of the umbra. Gas pressure in light bridges has also been found to dominate over magnetic pressure , and convective motions have been detected. The Wilson effect implies that sunspots are depressions on

812-540: Is also observed in most other solar activity and is linked to a variation in the solar magnetic field that changes polarity with this period. Early in the cycle, sunspots appear at higher latitudes and then move towards the equator as the cycle approaches maximum, following Spörer's law . Spots from two sequential cycles co-exist for several years during the years near solar minimum. Spots from sequential cycles can be distinguished by direction of their magnetic field and their latitude. The Wolf number sunspot index counts

870-496: Is because the luminance of a heated black body (closely approximated by the photosphere) at these temperatures varies greatly with temperature. Isolated from the surrounding photosphere, a single sunspot would shine brighter than the full moon , with a crimson-orange color. In some forming and decaying sunspots, relatively narrow regions of bright material appear penetrating into or completely dividing an umbra. These formations, referred to as light bridges, have been found to have

928-698: Is possible that TSI was actually higher in the Maunder Minimum compared to present-day levels, but uncertainties are high, with best estimates in the range ± 0.5   W ⋅ m − 2 {\displaystyle \pm 0.5\ \mathrm {W\cdot m^{-2}} } with a 2 σ {\displaystyle 2\sigma } uncertainty range of ± 1   W ⋅ m − 2 {\displaystyle \pm 1\ \mathrm {W\cdot m^{-2}} } . Sunspots, with their intense magnetic field concentrations, facilitate

986-408: Is used to protect the mirrors when they are not in use. The special shed for the telescope was completed during the summer. It consisted of a steel framework with an interior canvas covering that is coated with fireproof paint. The canvas side opposite the Sun is lowered to improve circulation through the vents. The structure was built on the highest point of the site, mounted as high as possible about

1044-699: The 6-meter VHF band . Solar activity (and the solar cycle) have been implicated as a factor in global warming . The first possible example of this is the Maunder Minimum period of low sunspot activity which occurred during the Little Ice Age in Europe. However, detailed studies from multiple paleoclimate indicators show that the lower northern hemisphere temperatures in the Little Ice Age began while sunspot numbers were still high before

1102-404: The solar maxima trend of sunspot count was upwards; for the following 60 years the trend was mostly downwards. Overall, the Sun was last as active as the modern maximum over 8,000 years ago. Sunspot number is correlated with the intensity of solar radiation over the period since 1979, when satellite measurements became available. The variation caused by the sunspot cycle to solar output is on

1160-482: The 60-foot and 150-foot tower telescopes at Mt. Wilson, the Snow telescope was only employed on an intermittent basis. Still, daily photographs of the Sun continued to be taken for a period of over 12 years, and thereafter the Snow telescope was still used when observations required a mirror rather than a lens. In 1911, the telescope underwent a significant overhaul with the goal of making it fireproof. The canvas louvers on

1218-648: The Snow Telescope to Mt. Wilson, so Hale instead brought a smaller solar telescope that had been used during the 1900 solar eclipse . Finally, in April 1904 Snow dropped her objections and allowed the relocation of the horizontal telescope to the Mt. Wilson station. The initial funding for this project came from a $ 10,000 grant by the Carnegie Institution, plus personal funds provided by Hale. The telescope

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1276-410: The Sun and reflect the illumination onto a second mirror, which directed the light horizontally onto a concave objective mirror. The optical train produced an image of the Sun that could be examined with a spectroheliograph . The advantage of this arrangement is that the observing instruments are held steady in laboratory conditions, allowing the use of bulky devices that cannot be readily attachment to

1334-507: The Sun are commonly called starspots , and both light and dark spots have been measured. The earliest record of sunspots is found in the Chinese I Ching , completed before 800 BC. The text describes that a dou and mei were observed in the sun, where both words refer to a small obscuration. The earliest record of a deliberate sunspot observation also comes from China, and dates to 364 BC, based on comments by astronomer Gan De (甘德) in

1392-469: The Sun in comparison with its brightness at the solar-minimum level. This is a difference in total solar irradiance at Earth over the sunspot cycle of close to 1.37   W ⋅ m − 2 {\displaystyle 1.37\ \mathrm {W\cdot m^{-2}} } . Other magnetic phenomena which correlate with sunspot activity include faculae and the chromospheric network. The combination of these magnetic factors mean that

1450-412: The Sun's atmosphere. The astronomers also found evidence of a magnetic field associated with sunspots. Until 1908, the Snow telescope was the only significant research telescope available to the observers at Mt. Wilson. However, the image quality was found to be impacted by rising air currents from the sunlit ground, for which issue a vertical tower telescope was a better design. With the completion of

1508-424: The Sun's surface. The appearance of an individual sunspot may last anywhere from a few days to a few months, though groups of sunspots and their associated active regions tend to last weeks or months. Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from 16 km (10 mi) to 160,000 km (100,000 mi). Although the details of sunspot formation are still

1566-493: The Sun's; spectroscopy examined the structure of starspot regions by analyzing variations in spectral line splitting due to the Zeeman effect; Doppler imaging showed differential rotation of spots for several stars and distributions different from the Sun's; spectral line analysis measured the temperature range of spots and the stellar surfaces. For example, in 1999, Strassmeier reported the largest cool starspot ever seen rotating

1624-411: The Sun, along with specific features of sunspots and flocculi . The rotation of the Sun was investigated with a spectroscope, along with bolographic investigation of the solar absorption . A notable finding of the telescope observations was that sunspots appeared cooler than the rest of the Sun's surface. The introduction of a hydrogen alpha filter in March 1908 led to the discovery of vortices in

1682-429: The age of 29, his reports remained obscure and were overshadowed by the independent discoveries of and publications about sunspots by Christoph Scheiner and Galileo Galilei . Galileo likely began telescopic sunspot observations around the same time as Harriot; however, Galileo's records did not start until 1612. During the next decades numerous astronomers of that era participated in the pursuit of sunspots. One of these

1740-461: The approximately 11-year solar cycle . Individual sunspots or groups of sunspots may last anywhere from a few days to a few months, but eventually decay. Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from 16 km (10 mi) to 160,000 km (100,000 mi). Larger sunspots can be visible from Earth without the aid of a telescope . They may travel at relative speeds , or proper motions , of

1798-420: The average number of sunspots and groups of sunspots during specific intervals. The 11-year solar cycles are numbered sequentially, starting with the observations made in the 1750s. George Ellery Hale first linked magnetic fields and sunspots in 1908. Hale suggested that the sunspot cycle period is 22 years, covering two periods of increased and decreased sunspot numbers, accompanied by polar reversals of

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1856-417: The bells remain unexposed to the weather. There are examples of architects who use louvers as part of the overall aesthetic effect of their buildings. The most well-known example is Finnish modernist architect Alvar Aalto who would create aesthetic effects in the facades of his buildings through the combination of different types and sizes of louvers, some fixed some moveable, and made mostly from wood (e.g.,

1914-406: The circumference of the Sun as sunspots rotate through the horizon. Since looking directly at the Sun with the naked eye permanently damages human vision , amateur observation of sunspots is generally conducted using projected images, or directly through protective filters . Small sections of very dark filter glass , such as a #14 welder's glass, are effective. A telescope eyepiece can project

1972-571: The coelostat telescope was rebuilt in a permanent wooden shed located on the north side of the observatory. It was dedicated on October 3, 1903 and named the Snow Horizontal Telescope after her father, George W. Snow , the man sometimes credited with the invention of balloon framing . However, the performance of the new instrument proved less than satisfactory, and, given the climate and atmospheric conditions in Wisconsin, this

2030-551: The complex transfer of energy and momentum to the upper solar atmosphere. This transfer occurs through a variety of mechanisms, including generated waves in the lower solar atmosphere and magnetic reconnection events. In 1947, G. E. Kron proposed that starspots were the reason for periodic changes in brightness on red dwarfs . Since the mid-1990s, starspot observations have been made using increasingly powerful techniques yielding more and more detail: photometry showed starspot growth and decay and showed cyclic behavior similar to

2088-446: The construction of buildings using louver in bushfire -prone areas in order to improve their resistance to bushfire attack from burning embers, radiant heat, flame contact and combinations of the three attack forms. The revised building standard details various construction methods and materials that must be used depending on the homes level of bushfire risk. This includes changes to the window and glazing requirements for homes located in

2146-477: The exterior were replaced with painted steel sheets, and the wooden roof was converted to steel. A concrete floor was laid, and the electrical wiring and controls were overhauled. By 1927, a 30-foot (9.1 m) spectrograph well had been dug. During the 1950s and 1960s, the University of Michigan attached an infrared spectrometer to the telescope and used it to study the Sun's infrared spectrum. Starting 1990, it

2204-433: The giant K0  star XX Trianguli (HD 12545) with a temperature of 3,500 K (3,230 °C), together with a warm spot of 4,800 K (4,530 °C). Louver A louver ( American English ) or louvre ( British English ; see spelling differences ) is a window blind or shutter with horizontal slats that are angled to admit light and air, but to keep out rain and direct sunshine. The angle of

2262-412: The heated ground, within the limitations of the budget. Skirt-like louvers surrounded the structure, protecting the interior from sunlight but allowing air circulation. Roof ventilation is used to further circulate air. Due to a slope of the ground, the shed has a 5° downward slope from front to back. It is oriented 15° east of north. Two spectrohelioscopes and three spectrograms are available for studying

2320-517: The image, without filtration, onto a white screen where it can be viewed indirectly, and even traced, to follow sunspot evolution. Special purpose hydrogen-alpha narrow bandpass filters and aluminum-coated glass attenuation filters (which have the appearance of mirrors due to their extremely high optical density ) on the front of a telescope provide safe observation through the eyepiece. Due to their correlation with other kinds of solar activity , sunspots can be used to help predict space weather ,

2378-459: The image. During testing it was found that the heat from the Sun caused the focal length of the mirrors to change. Observation of the Sun was found to be closest to optimal about an hour after sunrise. This time was also useful for minimizing the change in shape. Due to increased absorption of the atmosphere when the Sun is low, this required a longer exposure with the spectroheliograph. In order to minimize heat problems, an adjustable canvas screen

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2436-507: The order of 0.1% of the solar constant (a peak-to-trough range of 1.3 W·m compared with 1366 W·m for the average solar constant). Sunspots are observed with land-based and Earth-orbiting solar telescopes . These telescopes use filtration and projection techniques for direct observation, in addition to various types of filtered cameras. Specialized tools such as spectroscopes and spectrohelioscopes are used to examine sunspots and sunspot areas. Artificial eclipses allow viewing of

2494-449: The relationship of sunspot numbers to Total Solar Irradiance (TSI) over the decadal-scale solar cycle, and their relationship for century timescales, need not be the same. The main problem with quantifying the longer-term trends in TSI lies in the stability of the absolute radiometry measurements made from space, which has improved in recent decades but remains a problem. Analysis shows that it

2552-597: The relative absence of sunspots from July 1795 to January 1800 and was perhaps the first to construct a past record of observed or missing sunspots. From this he found that the absence of sunspots coincided with high wheat prices in England. The president of the Royal Society commented that the upward trend in wheat prices was due to monetary inflation . Years later scientists such as Richard Carrington in 1865 and John Henry Poynting in 1884 tried and failed to find

2610-440: The shape of faces where the smoke and steam from cooking would pour out through the eyes and mouth, or into constructions that were more like modern louvers, with slats that could be opened or closed by pulling on a string. Modern louvers are often made of aluminum , metal, wood, or glass. They may be opened and closed with a metal lever, pulleys, or through motorized operators. The Australian Standard specifies requirements for

2668-473: The slats may be adjustable, usually in blinds and windows, or fixed. Louvers originated in the Middle Ages as lantern-like constructions in wood that were fitted on top of roof holes in large kitchens to allow ventilation while keeping out rain and snow. They were originally rather crude constructions consisting merely of a barrel. Later, they evolved into more elaborate designs made of pottery, taking

2726-422: The solar magnetic dipole field. Horace W. Babcock later proposed a qualitative model for the dynamics of the solar outer layers. The Babcock Model explains that magnetic fields cause the behavior described by Spörer's law, as well as other effects, which are twisted by the Sun's rotation. Sunspot numbers also change over long periods. For example, during the period known as the modern maximum from 1900 to 1958

2784-446: The start of the Maunder Minimum, and persisted until after the Maunder Minimum had ceased. Numerical climate modelling indicates that volcanic activity was the main driver of the Little Ice Age . Sunspots themselves, in terms of the magnitude of their radiant-energy deficit, have a weak effect on solar flux. The total effect of sunspots and other magnetic processes in the solar photosphere is an increase of roughly 0.1% in brightness of

2842-468: The state of the ionosphere , and conditions relevant to short-wave radio propagation or satellite communications . High sunspot activity is celebrated by members of the amateur radio community as a harbinger of excellent ionospheric propagation conditions that greatly increase radio range in the HF bands. During peaks in sunspot activity, worldwide radio communication can be achieved on frequencies as high as

2900-423: The surface area through which the magnetic field passes to look dark against the bright background of photospheric granules . Sunspots initially appear in the photosphere as small darkened spots lacking a penumbra. These structures are known as solar pores. Over time, these pores increase in size and move towards one another. When a pore gets large enough, typically around 3,500 km (2,000 mi) in diameter,

2958-532: The various buildings of the Helsinki University of Technology ). A second example, taking influence from Aalto, is the second-generation modernist architect Juha Leiviskä . Louvers may be used as a type of flood opening , usually covered by one or more moving flaps. They are designed to allow floodwaters to enter and leave the building, equalizing hydrostatic pressure on the walls and mitigating structural damage due to flooding. Louver windows are

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3016-481: The viewing conditions to be excellent for solar observation. Although funds for the observatory were not forthcoming from the Carnegie Institution, Hale did manage to obtain funds from J. D. Hooker to help defray the cost of bringing the Bruce photographic telescope to the Mt. Wilson station of Yerkes Observatory. Hale's team set up their base on Mt. Wilson on February 29, 1904. Helen Snow was initially opposed to moving

3074-658: Was dedicated for the use of students and amateur astronomers. Sunspot Sunspots are temporary spots on the Sun's surface that are darker than the surrounding area. They are one of the most recognizable Solar phenomena and despite the fact that they are mostly visible in the solar photosphere they usually affect the entire solar atmosphere . They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection . Sunspots appear within active regions , usually in pairs of opposite magnetic polarity . Their number varies according to

3132-620: Was not expected to improve. In 1902, Hale had been named secretary to an advisory committee on astronomy for the recently-formed Carnegie Institution of Washington . He proposed to the committee the construction of a reflecting telescope with a 60-inch (150 cm) aperture, to be located on a mountain site with favorable viewing conditions near the Pacific coast. After gaining some encouraging interest, in June 1903 Hale traveled to Mt. Wilson accompanied by E. C. Pickering and W. Hussey . Hale found

3190-472: Was packed up for transport by mid-1904. Regular funding for the observatory was obtained from the Carnegie Institute later that year. The Snow telescope was transported up the narrow mountain trail in parts using a small, specially-designed carriage towed by horses. The Snow telescope was first set up during January, 1905, but due to rain the mirrors were not mounted until March 15. The coelostat

3248-476: Was placed on a carriage that can be moved east-west, which in turn is mounted on a 24-foot (7.3 m) pedestal. There are two concave mirrors with a diameter of 24 in (61 cm). The first mirror had a focal length of 60 ft (18 m), which produced an image of the Sun with a diameter of about 6.7 in (17.0 cm). The second had a longer focal length of 143 ft (44 m), yielding an image 16 in (40.6 cm) across. A wheeled housing

3306-498: Was the famous astronomer Johannes Hevelius who recorded 19 sunspot groups during the period of the early Maunder Minimum (1653-1679) in the book Machina Coelestis. In the early 19th Century, William Herschel was one of the first to hypothesize a connection of sunspots with temperatures on Earth and believed that certain features of sunspots would indicate increased heating on Earth. During his recognition of solar behavior and hypothesized solar structure, he inadvertently picked up

3364-448: Was used to shield the mirrors between exposures. Electric fans are also used successfully to cool the mirrors while they are in sunlight. Photographs of the 6.7 in (17 cm) diameter solar image are taken daily. It is also tested for use with taking spectra of bright stars, such as Antares . An original goal of the telescope was to make measurements of the solar constant over a full sunspot cycle . Daily photographs were taken of

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