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58-663: Mauna Loa Solar Observatory ( MLSO ) is a solar observatory located on the slopes of Mauna Loa on the island of Hawaii in the U.S. state of Hawaii . It is operated by the High Altitude Observatory (HAO), a laboratory within the National Center for Atmospheric Research (NCAR). The MLSO sits on property managed by the Mauna Loa Observatory (MLO), which is part of the U.S. Department of Commerce National Oceanic and Atmospheric Administration (NOAA). MLSO

116-516: 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

174-408: A coronal mass ejection, which consists of injection of energetic particles (primarily ionized hydrogen) into interplanetary space. Flares and CME are caused by sudden localized release of magnetic energy, which drives emission of ultraviolet and X-ray radiation as well as energetic particles. These eruptive phenomena can have a significant impact on Earth's upper atmosphere and space environment, and are

232-458: A direct relationship between the solar cycle and luminosity with a peak-to-peak amplitude of about 0.1%. Luminosity decreases by as much as 0.3% on a 10-day timescale when large groups of sunspots rotate across the Earth's view and increase by as much as 0.05% for up to 6 months due to faculae associated with large sunspot groups. The best information today comes from SOHO (a cooperative project of

290-456: A few times a day at solar maximum, down to one every few days at solar minimum. The size of these events themselves does not depend sensitively on the phase of the solar cycle. A case in point are the three large X-class flares that occurred in December 2006, very near solar minimum; an X9.0 flare on Dec 5 stands as one of the brightest on record. Along with the approximately 11-year sunspot cycle,

348-425: 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

406-440: A maximum activity back to a period of minimum activity. The magnetic field of the Sun flips during each solar cycle, with the flip occurring when the solar cycle is near its maximum. After two solar cycles, the Sun's magnetic field returns to its original state, completing what is known as a Hale cycle . This cycle has been observed for centuries by changes in the Sun's appearance and by terrestrial phenomena such as aurora but

464-476: A number of additional patterns and cycles have been hypothesized. The Waldmeier effect describes the observation that the maximum amplitudes of solar cycles are inversely proportional to the time between their solar minima and maxima. Therefore, cycles with larger maximum amplitudes tend to take less time to reach their maxima than cycles with smaller amplitudes. This effect was named after Max Waldmeier who first described it. The Gnevyshev–Ohl rule describes

522-430: A radiation flux of high-energy protons , sometimes known as solar cosmic rays. These can cause radiation damage to electronics and solar cells in satellites . Solar proton events also can cause single-event upset (SEU) events on electronics; at the same, the reduced flux of galactic cosmic radiation during solar maximum decreases the high-energy component of particle flux. CME radiation is dangerous to astronauts on

580-463: A solar cycle 25 Prediction Panel was made in early 2019. The Panel, which was organized by NOAA's Space Weather Prediction Center (SWPC) and NASA , based on the published solar cycle 25 predictions, concluded that solar cycle 25 will be very similar to solar cycle 24. They anticipate that the solar cycle minimum before cycle 25 will be long and deep, just as the minimum that preceded cycle 24. They expect solar maximum to occur between 2023 and 2026 with

638-453: A space mission who are outside the shielding produced by the Earth's magnetic field . Future mission designs ( e.g. , for a Mars Mission ) therefore incorporate a radiation-shielded "storm shelter" for astronauts to retreat to during such an event. Gleißberg developed a CME forecasting method that relies on consecutive cycles. The increased irradiance during solar maximum expands the envelope of

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696-566: A standard sunspot number index, the Wolf number , which continues to be used today. Between 1645 and 1715, very few sunspots were observed and recorded. This was first noted by Gustav Spörer and was later named the Maunder minimum after the wife-and-husband team Annie S. D. Maunder and Edward Walter Maunder who extensively researched this peculiar interval. In the second half of the nineteenth century Richard Carrington and Spörer independently noted

754-632: A sunspot range of 95 to 130, given in terms of the revised sunspot number. Solar cycle 24 began on 4 January 2008, with minimal activity until early 2010. The cycle featured a "double-peaked" solar maximum . The first peak reached 99 in 2011 and the second in early 2014 at 101. Cycle 24 ended in December 2019 after 11.0 years. Solar cycle 23 lasted 11.6 years, beginning in May ;1996 and ending in January ;2008. The maximum smoothed sunspot number (monthly number of sunspots averaged over

812-519: A twelve-month period) observed during the solar cycle was 120.8 (March 2000), and the minimum was 1.7. A total of 805 days had no sunspots during this cycle. Because the solar cycle reflects magnetic activity, various magnetically driven solar phenomena follow the solar cycle, including sunspots, faculae/plage, network, and coronal mass ejections. The Sun's apparent surface, the photosphere, radiates more actively when there are more sunspots. Satellite monitoring of solar luminosity revealed

870-448: Is a periodic 11-year change in the Sun 's activity measured in terms of variations in the number of observed sunspots on the Sun's surface . Over the period of a solar cycle, levels of solar radiation and ejection of solar material, the number and size of sunspots , solar flares , and coronal loops all exhibit a synchronized fluctuation from a period of minimum activity to a period of

928-498: 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

986-503: 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

1044-567: Is the amount of solar radiative energy incident on the Earth's upper atmosphere. TSI variations were undetectable until satellite observations began in late 1978. A series of radiometers were launched on satellites since the 1970s. TSI measurements varied from 1355 to 1375 W/m across more than ten satellites. One of the satellites, the ACRIMSAT was launched by the ACRIM group. The controversial 1989–1991 "ACRIM gap" between non-overlapping ACRIM satellites

1102-474: Is the varying photospheric coverage of these radiatively active solar magnetic structures. Energy changes in UV irradiance involved in production and loss of ozone have atmospheric effects. The 30 hPa atmospheric pressure level changed height in phase with solar activity during solar cycles 20–23. UV irradiance increase caused higher ozone production, leading to stratospheric heating and to poleward displacements in

1160-514: The European Space Agency and NASA ), such as the MDI magnetogram , where the solar "surface" magnetic field can be seen. As each cycle begins, sunspots appear at mid-latitudes, and then move closer and closer to the equator until a solar minimum is reached. This pattern is best visualized in the form of the so-called butterfly diagram. Images of the Sun are divided into latitudinal strips, and

1218-402: 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

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1276-521: The corona and heliosphere have been detected using carbon-14 and beryllium-10 cosmogenic isotopes stored in terrestrial reservoirs such as ice sheets and tree rings and by using historic observations of geomagnetic storm activity, which bridge the time gap between the end of the usable cosmogenic isotope data and the start of modern satellite data. These variations have been successfully reproduced using models that employ magnetic flux continuity equations and observed sunspot numbers to quantify

1334-463: The stratospheric and tropospheric wind systems. With a temperature of 5870 K, the photosphere emits a proportion of radiation in the extreme ultraviolet (EUV) and above. However, hotter upper layers of the Sun's atmosphere ( chromosphere and corona ) emit more short-wavelength radiation. Since the upper atmosphere is not homogeneous and contains significant magnetic structure, the solar ultraviolet (UV), EUV and X-ray flux varies markedly over

1392-487: The 400-year sunspot record, there is little evidence of the Suess cycle in the 400-year sunspot record by itself. Periodicity of solar activity with periods longer than the solar cycle of about 11 (22) years has been proposed, including: Sunspots eventually decay, releasing magnetic flux in the photosphere. This flux is dispersed and churned by turbulent convection and solar large-scale flows. These transport mechanisms lead to

1450-413: The Earth's atmosphere, causing low-orbiting space debris to re-enter more quickly. The outward expansion of solar ejecta into interplanetary space provides overdensities of plasma that are efficient at scattering high-energy cosmic rays entering the solar system from elsewhere in the galaxy. The frequency of solar eruptive events is modulated by the cycle, changing the degree of cosmic ray scattering in

1508-527: 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

1566-469: The Earth's surface. Their concentration can be measured in tree trunks or ice cores, allowing a reconstruction of solar activity levels into the distant past. Such reconstructions indicate that the overall level of solar activity since the middle of the twentieth century stands amongst the highest of the past 10,000 years, and that epochs of suppressed activity, of varying durations have occurred repeatedly over that time span. The total solar irradiance (TSI)

1624-464: The Earth). In 1919 they identified a number of patterns that would collectively become known as Hale's law : Hale's observations revealed that the complete magnetic cycle—which would later be referred to as a Hale cycle—spans two solar cycles, or 22 years, before returning to its original state (including polarity). Because nearly all manifestations are insensitive to polarity, the 11-year solar cycle remains

1682-593: 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. Solar Cycle The Solar cycle , also known as the solar magnetic activity cycle , sunspot cycle , or Schwabe cycle ,

1740-465: The accumulation of magnetized decay products at high solar latitudes, eventually reversing the polarity of the polar fields (notice how the blue and yellow fields reverse in the Hathaway/NASA/MSFC graph above). The dipolar component of the solar magnetic field reverses polarity around the time of solar maximum and reaches peak strength at the solar minimum. CMEs ( coronal mass ejections ) produce

1798-421: The average photosphere. This is caused by magnetized structures other than sunspots during solar maxima, such as faculae and active elements of the "bright" network, that are brighter (hotter) than the average photosphere. They collectively overcompensate for the irradiance deficit associated with the cooler, but less numerous sunspots. The primary driver of TSI changes on solar rotational and solar cycle timescales

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1856-404: 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

1914-485: The chromosphere, where they are referred to as plage. The evolution of plage areas is typically tracked from solar observations in the Ca II K line (393.37 nm). The amount of facula and plage area varies in phase with the solar cycle, and they are more abundant than sunspots by approximately an order of magnitude. They exhibit a non linear relation to sunspots. Plage regions are also associated with strong magnetic fields in

1972-405: The cycle, both in total irradiance and in its relative components (UV vs visible and other frequencies). The solar luminosity is an estimated 0.07 percent brighter during the mid-cycle solar maximum than the terminal solar minimum. Photospheric magnetism appears to be the primary cause (96%) of 1996–2013 TSI variation. The ratio of ultraviolet to visible light varies. TSI varies in phase with

2030-420: The data-driven solar dynamo and solar surface flux transport models seems to have predicted the strength of the solar polar field at the current minima correctly and forecasts a weak but not insignificant solar cycle 25 similar to or slightly stronger than cycle 24. Notably, they rule out the possibility of the Sun falling into a Maunder-minimum-like (inactive) state over the next decade. A preliminary consensus by

2088-514: The emergence of magnetic flux from the top of the solar atmosphere and into the heliosphere , showing that sunspot observations, geomagnetic activity and cosmogenic isotopes offer a convergent understanding of solar activity variations. The Suess cycle , or de Vries cycle , is a cycle present in radiocarbon proxies of solar activity with a period of about 210 years. It was named after Hans Eduard Suess and Hessel de Vries . Despite calculated radioisotope production rates being well correlated with

2146-508: The focus of research; however, the two halves of the Hale cycle are typically not identical: the 11-year cycles usually alternate between higher and lower sums of Wolf's sunspot numbers (the Gnevyshev-Ohl rule ). In 1961 the father-and-son team of Harold and Horace Babcock established that the solar cycle is a spatiotemporal magnetic process unfolding over the Sun as a whole. They observed that

2204-603: The grand challenges in astrophysics with major ramifications for space science and the understanding of magnetohydrodynamic phenomena elsewhere in the universe. The current scientific consensus on climate change is that solar variations only play a marginal role in driving global climate change , since the measured magnitude of recent solar variation is much smaller than the forcing due to greenhouse gases. Solar cycles have an average duration of about 11 years. Solar maximum and solar minimum refer to periods of maximum and minimum sunspot counts. Cycles span from one minimum to

2262-697: The longest of these (1784–1799) may actually have been two cycles. If so then the average length would be only around 10.7 years. Since observations began cycles as short as 9 years and as long as 14 years have been observed, and if the cycle of 1784–1799 is double then one of the two component cycles had to be less than 8 years in length. Significant amplitude variations also occur. Several lists of proposed historical "grand minima" of solar activity exist. Solar cycle 25 began in December 2019. Several predictions have been made for solar cycle 25 based on different methods, ranging from very weak to strong magnitude. A physics-based prediction relying on

2320-408: The monthly-averaged fractional surface of sunspots is calculated. This is plotted vertically as a color-coded bar, and the process is repeated month after month to produce this time-series diagram. While magnetic field changes are concentrated at sunspots, the entire sun undergoes analogous changes, albeit of smaller magnitude. Faculae are bright magnetic features on the photosphere. They extend into

2378-506: The next. The idea of a cyclical solar cycle was first hypothesized by Christian Horrebow based on his regular observations of sunspots made between 1761 and 1776 from the Rundetaarn observatory in Copenhagen , Denmark . In 1775, Horrebow noted how "it appears that after the course of a certain number of years, the appearance of the Sun repeats itself with respect to the number and size of

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2436-422: 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

2494-835: 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

2552-514: The outer solar system accordingly. As a consequence, the cosmic ray flux in the inner Solar System is anticorrelated with the overall level of solar activity. This anticorrelation is clearly detected in cosmic ray flux measurements at the Earth's surface. Some high-energy cosmic rays entering Earth's atmosphere collide hard enough with molecular atmospheric constituents that they occasionally cause nuclear spallation reactions . Fission products include radionuclides such as C and Be that settle on

2610-447: The past 11,400 years have been reconstructed using carbon-14 and beryllium-10 isotope ratios. The level of solar activity beginning in the 1940s is exceptional – the last period of similar magnitude occurred around 9,000 years ago (during the warm Boreal period ). The Sun was at a similarly high level of magnetic activity for only ~10% of the past 11,400 years. Almost all earlier high-activity periods were shorter than

2668-550: The phenomena of sunspots appearing at different heliographic latitudes at different parts of the cycle. (See Spörer's law .) Alfred Harrison Joy would later describe how the magnitude at which the sunspots are "tilted"—with the leading spot(s) closer to the equator than the trailing spot(s)―grows with the latitude of these regions. (See Joy's law .) The cycle's physical basis was elucidated by George Ellery Hale and collaborators, who in 1908 showed that sunspots were strongly magnetized (the first detection of magnetic fields beyond

2726-552: The present episode. Fossil records suggest that the solar cycle has been stable for at least the last 700 million years. For example, the cycle length during the Early Permian is estimated to be 10.62 years and similarly in the Neoproterozoic . Until 2009, it was thought that 28 cycles had spanned the 309 years between 1699 and 2008, giving an average length of 11.04 years, but research then showed that

2784-465: The primary drivers of what is now called space weather . Consequently, the occurrence of both geomagnetic storms and solar energetic particle events shows a strong solar cycle variation, peaking close to sunspot maximum. The occurrence frequency of coronal mass ejections and flares is strongly modulated by the cycle. Flares of any given size are some 50 times more frequent at solar maximum than at minimum. Large coronal mass ejections occur on average

2842-409: 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

2900-442: The solar magnetic activity cycle with an amplitude of about 0.1% around an average value of about 1361.5 W/m (the " solar constant "). Variations about the average of up to −0.3% are caused by large sunspot groups and of +0.05% by large faculae and the bright network on a 7-10-day timescale Satellite-era TSI variations show small but detectable trends. TSI is higher at solar maximum, even though sunspots are darker (cooler) than

2958-467: The solar surface is magnetized outside of sunspots, that this (weaker) magnetic field is to first order a dipole , and that this dipole undergoes polarity reversals with the same period as the sunspot cycle. Horace's Babcock Model described the Sun's oscillatory magnetic field as having a quasi-steady periodicity of 22 years. It covered the oscillatory exchange of energy between toroidal and poloidal solar magnetic field components. Sunspot numbers over

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3016-612: The solar surface. The solar magnetic field structures the corona, giving it its characteristic shape visible at times of solar eclipses. Complex coronal magnetic field structures evolve in response to fluid motions at the solar surface, and emergence of magnetic flux produced by dynamo action in the solar interior. For reasons not yet understood in detail, sometimes these structures lose stability, leading to solar flares and coronal mass ejections (CME). Flares consist of an abrupt emission of energy (primarily at ultraviolet and X-ray wavelengths), which may or may not be accompanied by

3074-504: The spots". The solar cycle however would not be clearly identified until 1843 when Samuel Heinrich Schwabe noticed a periodic variation in the average number of sunspots after 17 years of solar observations. Schwabe continued to observe the sunspot cycle for another 23 years, until 1867. In 1852, Rudolf Wolf designated the first numbered solar cycle to have started in February 1755 based on Schwabe's and other observations. Wolf also created

3132-412: The tendency for the sum of the Wolf number over an odd solar cycle to exceed that of the preceding even cycle. The Gleissberg cycle describes an amplitude modulation of solar cycles with a period of about 70–100 years, or seven or eight solar cycles. It was named after Wolfgang Gleißberg. As pioneered by Ilya G. Usoskin and Sami Solanki , associated centennial variations in magnetic fields in

3190-552: Was built in 1965. The MLSO is tasked with monitoring the solar atmosphere and recording data on plasmic and energetic emissions from the chromosphere and corona . Studies of coronal mass ejections (CMEs) are also conducted at MLSO. A number of non-solar astronomical observatories are located at the site. The MLSO instruments record images of the solar disk and limb every 3 minutes for 3–10 hours daily starting at 17:00 UT, weather permitting. Solar observatory Solar telescopes need optics large enough to achieve

3248-537: 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

3306-517: Was interpolated by the ACRIM group into a composite showing +0.037%/decade rise. Another series based on the ACRIM data is produced by the PMOD group and shows a −0.008%/decade downward trend. This 0.045%/decade difference can impact climate models. However, reconstructed total solar irradiance with models favor the PMOD series, thus reconciling the ACRIM-gap issue. Solar irradiance varies systematically over

3364-417: Was not clearly identified until 1843. Solar activity, driven by both the solar cycle and transient aperiodic processes, governs the environment of interplanetary space by creating space weather and impacting space- and ground-based technologies as well as the Earth's atmosphere and also possibly climate fluctuations on scales of centuries and longer. Understanding and predicting the solar cycle remains one of

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