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Sunspots are
phenomena A phenomenon ( : phenomena) is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be directly observed. Kant was heavily influenced by Gottfried W ...
on the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
's
photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of
magnetic flux In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ( ...
that inhibit
convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
. Sunspots appear within
active region An active region is a temporary region in the Sun's atmosphere characterized by a strong and complex magnetic field. They are often associated with sunspots and are commonly the source of violent eruptions such as coronal mass ejections and solar ...
s, usually in pairs of opposite
magnetic polarity A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
. Their number varies according to the approximately 11-year
solar cycle The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
. 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 to . Larger sunspots can be visible from Earth without the aid of a
telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...
. They may travel at
relative speed The relative velocity \vec_ (also \vec_ or \vec_) is the velocity of an object or observer B in the rest frame of another object or observer A. Classical mechanics In one dimension (non-relativistic) We begin with relative motion in the classi ...
s, or
proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
s, of a few hundred meters per second when they first emerge. Indicating intense magnetic activity, sunspots accompany other active region phenomena such as
coronal loop In solar physics, a coronal loop is a well-defined arch-like structure in the Sun's atmosphere made up of relatively dense plasma confined and isolated from the surrounding medium by magnetic flux tubes. Coronal loops begin and end at two f ...
s, prominences, and
reconnection Magnetic reconnection is a physical process occurring in highly conducting plasmas in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration. Magnetic reconnectio ...
events. Most
solar flare A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...
s and
coronal mass ejection A coronal mass ejection (CME) is a significant release of plasma and accompanying magnetic field from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accept ...
s originate in these magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s other than the Sun are commonly called
starspot Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...
s, and both light and dark spots have been measured.


History

The earliest record of sunspots is found in the Chinese ''
I Ching The ''I Ching'' or ''Yi Jing'' (, ), usually translated ''Book of Changes'' or ''Classic of Changes'', is an ancient Chinese divination text that is among the oldest of the Chinese classics. Originally a divination manual in the Western Zho ...
'', 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 Gan De (; fl. 4th century BC), also known as the Lord Gan (Gan Gong), was an ancient Chinese astronomer and astrologer born in the State of Qi. Along with Shi Shen, he is believed to be the first in history known by name to compile a star catal ...
(甘德) in 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 Western literature, also known as European literature, is the literature written in the context of Western culture in the languages of Europe, as well as several geographically or historically related languages such as Basque and Hungarian, an ...
is circa 300 BC, by
ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
scholar
Theophrastus Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek philosopher and the successor to Aristotle in the Peripatetic school. He was a native of Eresos in Lesbos.Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routledge ...
, student of
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution ...
and
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
and successor to the latter. The first drawings of sunspots were made by English monk
John of Worcester John of Worcester (died c. 1140) was an English monk and chronicler who worked at Worcester Priory. He is usually held to be the author of the ''Chronicon ex chronicis''. ''Chronicon ex chronicis'' The ''Chronicon ex chronicis'' is a world wi ...
in December 1128. Sunspots were first observed telescopically in December 1610 by English astronomer
Thomas Harriot Thomas Harriot (; – 2 July 1621), also spelled Harriott, Hariot or Heriot, was an English astronomer, mathematician, ethnographer and translator to whom the theory of refraction is attributed. Thomas Harriot was also recognized for his cont ...
. His observations were recorded in his notebooks and were followed in March 1611 by observations and reports by Frisian astronomers
Johannes Johannes is a Medieval Latin form of the personal name that usually appears as "John" in English language contexts. It is a variant of the Greek and Classical Latin variants (Ιωάννης, ''Ioannes''), itself derived from the Hebrew name '' Yeh ...
and
David Fabricius David Fabricius (9 March 1564 – 7 May 1617) was a German pastor who made two major discoveries in the early days of telescopic astronomy, jointly with his eldest son, Johannes Fabricius (1587–1615). David Fabricius (Latinization of his proper n ...
. After Johannes Fabricius' death at the age of 29, his reports remained obscure and were eclipsed by the independent discoveries of and publications about sunspots by
Christoph Scheiner Christoph Scheiner SJ (25 July 1573 (or 1575) – 18 June 1650) was a Jesuit priest, physicist and astronomer in Ingolstadt. Biography Augsburg/Dillingen: 1591–1605 Scheiner was born in Markt Wald near Mindelheim in Swabia, earlier markgrav ...
and
Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
. Galileo likely began telescopic sunspot observations around the same time as Harriot; however, Galileo's records did not start until 1612. In the early 19th Century,
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
was one of the first to equate sunspots with heating and cooling 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 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 The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
commented that the upward trend in wheat prices was due to
monetary inflation Monetary inflation is a sustained increase in the money supply of a country (or currency area). Depending on many factors, especially public expectations, the fundamental state and development of the economy, and the transmission mechanism, it ...
. Years later scientists such as
Richard Carrington Richard Christopher Carrington (26 May 1826 – 27 November 1875) was an English amateur astronomy, amateur astronomer whose 1859 astronomical observations demonstrated the existence of solar flares as well as suggesting their electrical influ ...
in 1865 and
John Henry Poynting John Henry Poynting FRS (9 September 185230 March 1914) was an English physicist. He was the first professor of physics at Mason Science College from 1880 to 1900, and then the successor institution, the University of Birmingham until his deat ...
in 1884 tried and failed to find a connection between wheat prices and sunspots, and modern analysis finds that there is no statistically significant correlation between wheat prices and sunspot numbers.


Physics


Morphology

Sunspots have two main structures: a central
umbra The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast. Th ...
and a surrounding
penumbra The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast. Th ...
. The umbra is the darkest region of a sunspot and is where the magnetic field is strongest and approximately vertical, or
normal Normal(s) or The Normal(s) may refer to: Film and television * ''Normal'' (2003 film), starring Jessica Lange and Tom Wilkinson * ''Normal'' (2007 film), starring Carrie-Anne Moss, Kevin Zegers, Callum Keith Rennie, and Andrew Airlie * ''Norma ...
, to the Sun's surface, or
photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
. The umbra may be surrounded completely or only partially by 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 is because the
luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...
of a heated
black body A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A 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 The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, 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 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 In physics, magnetic pressure is an energy density associated with a magnetic field. In SI units, the energy density P_B of a magnetic field with strength B can be expressed as :P_B = \frac where \mu_0 is the vacuum permeability. Any magnetic fiel ...
, and convective motions have been detected. The Wilson effect implies that sunspots are depressions on the Sun's surface.


Lifecycle

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 region An active region is a temporary region in the Sun's atmosphere characterized by a strong and complex magnetic field. They are often associated with sunspots and are commonly the source of violent eruptions such as coronal mass ejections and solar ...
s tend to last weeks or months. Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from to .


Formation

Although the details of sunspot formation are still a matter of ongoing research, it is widely understood that they are the visible manifestations of
magnetic flux tube A flux tube is a generally tube-like ( cylindrical) region of space containing a magnetic field, B, such that the cylindrical sides of the tube are everywhere parallel to the magnetic field lines. It is a graphical visual aid for visualizing a ma ...
s in the Sun's
convective zone A convection zone, convective zone or convective region of a star is a layer which is unstable due to convection. Energy is primarily or partially transported by convection in such a region. In a radiation zone, energy is transported by radiatio ...
projecting through the photosphere within active regions. Their characteristic darkening occurs due to this strong magnetic field inhibiting
convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
in the photosphere. As a result, the energy flux from the Sun's interior decreases, and with it, surface temperature, causing 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 in diameter, a penumbra will begin to form.


Decay

Magnetic pressure In physics, magnetic pressure is an energy density associated with a magnetic field. In SI units, the energy density P_B of a magnetic field with strength B can be expressed as :P_B = \frac where \mu_0 is the vacuum permeability. Any magnetic fiel ...
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 The Solar and Heliospheric Observatory (SOHO) is a European Space Agency (ESA) spacecraft built by a European industrial consortium led by Matra Marconi Space (now Airbus Defence and Space) that was launched on a Lockheed Martin Atlas IIAS lau ...
(SOHO) using sound waves traveling below the photosphere (local
helioseismology Helioseismology, a term coined by Douglas Gough, is the study of the structure and dynamics of the Sun through its oscillations. These are principally caused by sound waves that are continuously driven and damped by convection near the Sun's sur ...
) were used to develop a three-dimensional image of the internal structure below sunspots; these observations show that a powerful downdraft underneath each sunspot, forms a rotating
vortex In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...
that sustains the concentrated magnetic field.


Solar cycle

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 is also observed in most other
solar activity Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. These phenomena take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots. These phenomena are ...
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 Spörer's law predicts the variation of sunspot latitudes during a solar cycle. It was discovered by the English astronomer Richard Christopher Carrington around 1861. Carrington's work was refined by the German astronomer Gustav Spörer. At the ...
. 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 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 George Ellery Hale (June 29, 1868 – February 21, 1938) was an American solar astronomer, best known for his discovery of magnetic fields in sunspots, and as the leader or key figure in the planning or construction of several world-lea ...
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 the solar magnetic
dipole In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: *An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...
field.
Horace W. Babcock Horace Welcome Babcock (September 13, 1912 – August 29, 2003) was an American astronomer. He was the son of Harold D. Babcock. Career Babcock invented and built a number of astronomical instruments, and in 1953 was the first to propose th ...
later proposed a qualitative model for the dynamics of the solar outer layers. The
Babcock Model The Babcock Model describes a mechanism which can explain magnetic and sunspot patterns observed on the Sun. History The modern understanding of sunspots starts with George Ellery Hale, who linked magnetic fields and sunspots. Hale suggested t ...
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.


Longer-period trends

Sunspot numbers also change over long periods. For example, during the period known as the modern maximum from 1900 to 1958 the
solar maxima Solar maximum is the regular period of greatest solar activity during the Sun's 11-year solar cycle. During solar maximum, large numbers of sunspots appear, and the solar irradiance output grows by about 0.07%. On average, the solar cycle t ...
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 Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ( ...
over the period since 1979, when satellite measurements became available. The variation caused by the sunspot cycle to solar output is on the order of 0.1% of the solar constant (a peak-to-trough range of 1.3 W·m−2 compared with 1366 W·m−2 for the average solar constant).


Modern observation

Sunspots are observed with land-based and Earth-orbiting
solar telescope A solar telescope is a special purpose telescope used to observe the Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, the visible spectrum. Obsolete names for Sun telescopes include heliograph and photoheliograph ...
s. These telescopes use filtration and projection techniques for direct observation, in addition to various types of filtered cameras. Specialized tools such as
spectroscope An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...
s and
spectrohelioscope A spectrohelioscope is a type of solar telescope designed by George Ellery Hale in 1924 to allow the Sun to be viewed in a selected wavelength of light. The name comes from Latin- and Greek-based words: "Spectro," referring to the optical spectrum, ...
s are used to examine sunspots and sunspot areas. Artificial eclipses allow viewing of the circumference of the Sun as sunspots rotate through the horizon. Since looking directly at the Sun with the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
permanently damages
human vision Visual perception is the ability to interpret the surrounding environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum reflec ...
, amateur observation of sunspots is generally conducted using projected images, or directly through protective
filters Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...
. Small sections of very dark filter glass, such as a #14 welder's glass, are effective. A telescope
eyepiece An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through the device. The ...
can project 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 In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable att ...
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.


Application

Due to their correlation with other kinds of
solar activity Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. These phenomena take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots. These phenomena are ...
, sunspots can be used to help predict
space weather Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the ma ...
, the state of the
ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
, and conditions relevant to
short-wave Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 me ...
radio propagation Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affect ...
or
satellite communication A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...
s. 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 the 6-meter VHF band.
Solar activity Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. These phenomena take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots. These phenomena are ...
(and the solar cycle) have been implicated as a factor in
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
. The first possible example of this is the Maunder Minimum period of low sunspot activity which occurred during the Little Ice Age in Europe.PDF Copy
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 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 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\ \mathrm. Other magnetic phenomena which correlate with sunspot activity include
facula A facula (plural: faculae ), Latin for "little torch", is literally a "bright spot". The term has several common technical uses. It is used in planetary nomenclature for naming certain surface features of planets and moons,. and is also a type of ...
e and the chromospheric network. The combination of these magnetic factors mean that 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 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 \pm0.5\ \mathrm with a 2\sigma uncertainty range of \pm1\ \mathrm.


Starspot

In 1947, G. E. Kron proposed that
starspot Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...
s were the reason for periodic changes in brightness on
red dwarfs ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
. Since the mid-1990s, starspot observations have been made using increasingly powerful techniques yielding more and more detail:
photometry Photometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electro ...
showed starspot growth and decay and showed cyclic behavior similar to the Sun's;
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
examined the structure of starspot regions by analyzing variations in spectral line splitting due to the Zeeman effect;
Doppler imaging Inhomogeneous structures on stellar surfaces, i.e. temperature differences, chemical composition or magnetic fields, create characteristic distortions in the spectral lines due to the Doppler effect. These distortions will move across spectral l ...
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 the giant K0 star XX Triangulum (HD 12545) with a temperature of , together with a warm spot of .


See also

*''
Letters on Sunspots '' Letters on Sunspots '' (''Istoria e Dimostrazioni intorno alle Macchie Solari'') was a pamphlet written by Galileo Galilei in 1612 and published in Rome by the Accademia dei Lincei in 1613. In it, Galileo outlined his recent observation of dar ...
'' * Joy's law *
List of solar cycles Solar cycles are nearly periodic 11-year changes in the Sun's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to start in 1755 when Rudolf Wolf began extensive reporting ...
*
Radio propagation Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affect ...
*
Solar cycle The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
*
Solar rotation Solar rotation varies with latitude. The Sun is not a solid body, but is composed of a gaseous plasma. Different latitudes rotate at different periods. The source of this differential rotation is an area of current research in solar astronomy. ...
*
Space weather Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the ma ...
*
Spörer's law Spörer's law predicts the variation of sunspot latitudes during a solar cycle. It was discovered by the English astronomer Richard Christopher Carrington around 1861. Carrington's work was refined by the German astronomer Gustav Spörer. At the ...
*
Starspot Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...
*
Wolf number The Wolf number (also known as the relative sunspot number or Zürich number) is a quantity that measures the number of sunspots and groups of sunspots present on the surface of the Sun. History Astronomers have been observing the Sun recordi ...


References


Further reading

*


External links


Sunspot Database based on Terrestrial (GPR/DPD) and Satellite (SOHO/SDO) observations from 1872 to Nowadays with the newest data.
()
Solar Cycle 24 and VHF Aurora Website (www.solarcycle24.com)

Belgium World Data Center for the sunspot index




Impressive collection of sunspot images
NOAA Solar Cycle Progression
Current solar cycle. ** Current conditions:
Space weather Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the ma ...

Lockheed Martin Solar and Astrophysics Lab

Sun, trek website
An educational resource for teachers and students about the Sun and its effect on the Earth * Tools to display the current sunspot number in a browser *

** ttp://www.n0hr.com/Ham_Radio_Toolbar.htm HamLinks Toolbar – displays solar flux, A Index and K Index data in a toolbar
The Sharpest View of the Sun

Daily Sunspot Update and Picture of the Sun (www.spaceweather.com)
(University of South Wales)


Sunspot data

* ** * ** *** International Sunspot Numbersunspot maximum and minimum 1610–present; annual numbers 1700–present; monthly numbers 1749–present; daily values 1818–present; and sunspot numbers by north and south hemisphere. The McNish–Lincoln sunspot prediction is also included. *** American sunspot numbers 1945–present *** Ancient sunspot data 165 BC to 1684 AD *** Group Sunspot Numbers (Doug Hoyt re-evaluation) 1610–1995 * {{Authority control Solar phenomena Vortices Articles containing video clips