Sunspots imaged by the MDI instrument on NASA’s Solar and Heliospheric Observatory (SOHO) on 30 March 2001. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December Events 240 BC - 1st recorded Perihelion passage of Halley's Comet. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. It was the source of numerous flares and coronal mass ejections, including one of the largest flares recorded in 25 years on 2 April 2001. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. Events 68 - Galba, Governor of Hispania, names himself legatus senatus populique Romani, breaking the line of Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar.

A sunspot is a region on the Sun's surface (photosphere) that is marked by a lower temperature than its surroundings and has intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. The Sun (Sol is the Star at the center of the Solar System. In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. Convection in the most general terms refers to the movement of molecules within Fluids (i They can be visible from Earth without the aid of a telescope. Although they are blindingly bright at temperatures of roughly 4000-4500 K, the contrast with the surrounding material at about 5800 K leaves them clearly visible as dark spots, as the intensity of a heated black body (closely approximated by the photosphere) is a function of T to the fourth power. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic In Physics, a black body is an object that absorbs all light that falls on it If a sunspot was isolated from the surrounding photosphere it would be brighter than an electric arc. An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive A minimum in the eleven-year sunspot cycle may happen between 2007 and 2008 [1] and while the observation of a reverse polarity sunspot ^[1] on 4 January 2008 the 1st Cycle 24 sunspot was sighted, no additional sunspots have yet been seen in this cycle. Solar variations are changes in the amount of Solar radiation emitted by the Sun. Events 46 BC - Titus Labienus defeats Julius Caesar in the Battle of Ruspina. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common The definition of a new sunspot cycle is when the average number of sunspots of the new cycle's magnetic polarity outnumber those of the old cycle's polarity. Forecasts in 2006 expected cycle 24 to start between late 2007 and early 2008, but new estimates suggest a delay until 2009. Sunspots, being the manifestation of intense magnetic activity, host secondary phenomena such as coronal loops and reconnection events. Coronal loops form the basic structure of the lower Corona and Transition region of the Sun. Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. Similar phenomena indirectly observed on stars are commonly called starspots and both light and dark spots have been measured. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth ^[2]

Sunspot variation

Main article: Solar variation

400 year sunspot history

11,000 year sunspot reconstruction

A drawing of a sunspot in the Chronicles of John of Worcester. Solar variations are changes in the amount of Solar radiation emitted by the Sun. John of Worcester (died Circa 1140 was an English Monk and chronicler.

Sunspot populations quickly rise and more slowly fall on an irregular cycle about every 11 years. Significant variations of the 11 year period are known over longer spans of time. For example, from 1900 to the 1960s the solar maxima trend of sunspot count has been upward from the 1960s to the present, it has diminished somewhat. ^[3]. The Sun is presently at a markedly heightened level of sunspot activity and was last similarly active over 8,000 years ago. The number of sunspots correlates with the intensity of solar radiation over the period (since 1979) when satellite measurements of absolute radiative flux were available. Since sunspots are darker than the surrounding photosphere it might be expected that more sunspots would lead to less solar radiation and a decreased solar constant. However, the surrounding margins of sunspots are hotter than the average, and so are brighter& overall, more sunspots increase the sun's solar constant or brightness. The variation caused by the sunspot cycle to solar output is relatively small, on the order of 0. 1% of the solar constant (a peak-to-trough range of 1. 3 W m^-2 compared to 1366 W m^-2 for the average solar constant)^[4][5]. This range is slightly smaller than the change in radiative forcing caused by the increase in atmospheric CO₂ since the 18th century^[6]. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single During the Maunder Minimum in the 17th Century there were hardly any sunspots at all. The Maunder Minimum is the name given to the period roughly from 1645 to 1715, when Sunspots became exceedingly rare as noted by solar observers of This coincides with a period of cooling known as the Little Ice Age. The Little Ice Age (LIA was a period of cooling occurring after a warmer era known as the Medieval Warm Period or Medieval Climate Optimum It has been speculated that there may be a resonant gravitational link between a photospheric tidal force from the planets, the dominant component by summing gravitational tidal force (75% being Jupiter's) with an 11 year cycle^[7].

History

Apparent references to sunspots were made by Chinese astronomers in 28 BC (Hanshu, 27), who probably could see the largest spot groups when the sun's glare was filtered by wind-borne dust from the various central Asian deserts. This is a Timeline of Chinese records and investigations in Astronomy. The Book of Han ( is a classic Chinese Historical writing completed in 111 CE covering the history of Western Han from 206 BCE to A large sunspot was also seen at the time of Charlemagne's death in 813 A. Charlemagne (ˈʃɑrlɨmeɪn Carolus Magnus or Karolus Magnus meaning Charles the Great) (747 – 28 January 814 was King of the Franks from 768 to his D. and sunspot activity in 1129 was described by John of Worcester. John of Worcester (died Circa 1140 was an English Monk and chronicler. However, these observations were misinterpreted until Galileo gave the correct explanation in 1612. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher

They were first observed telescopically in late 1610 by the English astronomer Thomas Harriot and Frisian astronomers Johannes and David Fabricius, who published a description in June 1611. Thomas Harriot ( c 1560 – 2 July 1621) was an English astronomer, Mathematician, Ethnographer, and Translator Johann(es Fabricius ( 8 January 1587 &ndash 19 March 1616) eldest son of David Fabricius (1564-1617 was a Frisian / David Fabricius ( March 9, 1564, Esens - May 7, 1617, Osteel) was a German theologian who made two major At the latter time Galileo had been showing sunspots to astronomers in Rome, and Christoph Scheiner had probably been observing the spots for two or three months. Christoph Scheiner SJ ( 25 July 1573 (or 1575 in Markt Wald near Mindelheim in Swabia The ensuing priority dispute between Galileo and Scheiner, neither of whom knew of the Fabricius' work, was thus as pointless as it was bitter.

Sunspots had some importance in the debate over the nature of the solar system. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. They showed that the Sun rotated, and their comings and goings showed that the Sun changed, contrary to the teaching of Aristotle. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. The details of their apparent motion could not be readily explained except in the heliocentric system of Copernicus. In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System.

The cyclic variation of the number of sunspots was first observed by Heinrich Schwabe between 1826 and 1843 and led Rudolf Wolf to make systematic observations starting in 1848. Samuel Heinrich Schwabe ( October 25, 1789 &ndash April 11, 1875) a German Astronomer remembered for his work on Sunspots Johann Rudolf Wolf ( 7 July 1816 – 6 December 1893) was a Swiss astronomer and Mathematician best known for The Wolf number is an expression of individual spots and spot groupings, which has demonstrated success in its correlation to a number of solar observables. Also in 1848, Joseph Henry projected an image of the Sun onto a screen and determined that sunspots were cooler than the surrounding surface. Joseph Henry ( December 17 1797 &ndash May 13 1878) was an American scientist who served as the first Secretary of the Smithsonian ^[8]

Wolf also studied the historical record in an attempt to establish a database on cyclic variations of the past. He established a cycle database to only 1700, although the technology and techniques for careful solar observations were first available in 1610. Gustav Spörer later suggested a 70-year period before 1716 in which sunspots were rarely observed as the reason for Wolf's inability to extend the cycles into the seventeenth century. Friederich Wilhelm Gustav Spörer ( October 23 1822 &ndash July 7 1895) was a German Astronomer. The economist William Stanley Jevons suggested that there is a relationship between sunspots and crises in business cycles. William Stanley Jevons ( September 1, 1835 - August 13, 1882) English Economist and Logician, was born in He reasoned that sunspots affect earth's weather, which, in turn, influences crop yields and, therefore, the economy.

Edward Maunder would later suggest a period over which the Sun had changed modality from a period in which sunspots all but disappeared from the solar surface, followed by the appearance of sunspot cycles starting in 1700. Edward Walter Maunder ( April 12 1851 &ndash March 21 1928) was an English Astronomer best remembered for his study of Sunspots Careful studies revealed the problem not to be a lack of observational data but included references to negative observations. Adding to this understanding of the absence of solar activity cycles were observations of aurorae, which were also absent at the same time. Even the lack of a solar corona during solar eclipses was noted prior to 1715. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured

Sunspot research was dormant for much of the 17th and early 18th centuries because of the Maunder Minimum, during which no sunspots were visible for some years; but after the resumption of sunspot activity, Heinrich Schwabe in 1843 reported a periodic change in the number of sunspots. The Maunder Minimum is the name given to the period roughly from 1645 to 1715, when Sunspots became exceedingly rare as noted by solar observers of Since 1981, the Royal Observatory of Belgium keeps track of sunspots as the World data center for the Sunspot Index. The Royal Observatory of Belgium, officially known in French as the Observatoire Royal de Belgique, and in Dutch as the Koninklijke Sterrenwacht van

Radio communications interference

Solar flares also create a wide spectrum of radio noise; at VHF (and under unusual conditions at HF) this noise may interfere directly with a wanted signal. The frequency with which a radio operator experiences solar flare effects will vary with the approximately 11-year sunspot cycle; more effects occur during solar maximum (when flare occurrence is high) than during solar minimum (when flare occurrence is very low). A radio operator can experience great difficulty in transmitting or receiving signals during solar flares due to more noise and different propagation patterns.

Significant events

An extremely powerful flare was emitted toward Earth on 1 September 1859. A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares Events 462 - Possible start of first Byzantine indiction cycle. Year 1859 ( MDCCCLIX) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Common It interrupted electrical telegraph service and caused visible Aurora Borealis as far south as Havana, Hawaii, and Rome with similar activity in the southern hemisphere.

The most powerful flare observed by satellite instrumentation began on 4 November 2003 at 19:29 UTC, and saturated instruments for 11 minutes. Events 1333 - Flood of the Arno River, causing massive damage in Florence as recorded by the Florentine chronicler Giovanni Villani Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Region 486 has been estimated to have produced an X-ray flux of X28. Holographic and visual observations indicate significant activity continued on the far side of the Sun.

Physics

A sunspot viewed close-up in ultraviolet light, taken by the TRACE spacecraft. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays TRACE ( Transition Region and Coronal Explorer) is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and

Main article: Solar cycle

Although the details of sunspot generation are still somewhat a matter of research, it is quite clear that sunspots are the visible counterparts of magnetic flux tubes in the convective zone of the sun that get "wound up" by differential rotation. The solar cycle, or the solar magnetic activity cycle, is the main source of periodic variation of all solar phenomena driving variations in Space weather. A fluxon is a quantum of electromagnetic flux and may have one of several meanings Electromagnetic Behavior In Theoretical physics, fluxons The convection zone of a Star is the range of radii in which energy is transported primarily by Convection. Differential rotation is seen when different parts of a rotating object move with different angular velocities (rates of Rotation) If the stress on the flux tubes reaches a certain limit, they curl up quite like a rubber band and puncture the sun's surface. At the puncture points convection is inhibited, the energy flux from the sun's interior decreases, and with it the surface temperature.

The Wilson effect tells us that sunspots are actually depressions on the sun's surface. In 1769 a Scottish astronomer named Alexander Wilson noticed that the shape of Sunspots noticeably flattened as they approached the Sun 's limb due to the This model is supported by observations using the Zeeman effect that show that prototypical sunspots come in pairs with opposite magnetic polarity. The Zeeman effect (ˈzeɪmɑːn is the splitting of a Spectral line into several components in the presence of a static Magnetic field. From cycle to cycle, the polarities of leading and trailing (with respect to the solar rotation) sunspots change from north/south to south/north and back. Sunspots usually appear in groups.

The sunspot itself can be divided into two parts:

• The central umbra, which is the darkest part, where the magnetic field is approximately vertical
• The surrounding penumbra, which is lighter, where the magnetic field lines are more inclined.

Magnetic field lines would ordinarily repel each other, causing sunspots to disperse rapidly, but sunspot lifetime is about two weeks. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges Recent observations from the Solar and Heliospheric Observatory (SOHO) using sound waves traveling through the Sun's photosphere to develop a detailed image of the internal structure below sunspots show that there is a powerful downdraft underneath each sunspot, forming a rotating vortex that concentrates magnetic field lines. The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December V erification of the O rigins of R otation in T ornadoes Ex periment or VORTEX, is a field project that seeks to understand how a Sunspots are self-perpetuating storms, similar in some ways to terrestrial hurricanes. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding

Butterfly diagram showing paired Spörer's law behavior. Spörer's law predicts the variation of Sunspot latitudes during a Solar cycle.

Sunspot activity cycles about every eleven years. The point of highest sunspot activity during this cycle is known as Solar Maximum, and the point of lowest activity is Solar Minimum. At the start of a cycle, sunspots tend to appear in the higher latitudes and then move towards the equator as the cycle approaches maximum: this is called Spörer's law. Spörer's law predicts the variation of Sunspot latitudes during a Solar cycle.

Today it is known that there are various periods in the Wolf number sunspot index, the most prominent of which is at about 11 years in the mean. This period is also observed in most other expressions of solar activity and is deeply linked to a variation in the solar magnetic field that changes polarity with this period, too. Solar variations are changes in the amount of Solar radiation emitted by the Sun.

A modern understanding of sunspots starts with George Ellery Hale, in which magnetic fields and sunspots are linked. George Ellery Hale ( June 29 1868 &ndash February 21 1938) was an American solar Astronomer, born in Chicago Hale suggested that the sunspot cycle period is 22 years, covering two polar reversals of 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 the behavior described by Spörer's law, as well as other effects, as being due to magnetic fields which are twisted by the Sun's rotation. The Babcock Model describes a mechanism which can explain magnetic and Sunspot patterns observed on the Sun.

Sunspot observation

The 1 m Swedish Solar Telescope at Roque de los Muchachos Observatory, La Palma in the Canary Islands. The Swedish Solar Telescope (or SST is a 1 m telescope at Roque de los Muchachos Observatory, La Palma in the Canary Islands. Roqué de los Muchachos Observatory is an Astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Isla de La Palma (known in English as "La Palma" not to be confused with "Palma" in the Balearic Islands is a Spanish volcanic ocean island The Canary Islands ( English pronunciation kəˈnæriː ˈaɪləndz Spanish: Islas Canarias, ˈizlas kaˈnarjas are a Spanish

Sunspots are observed with land-based solar telescopes as well as ones on Earth-orbiting satellites. A solar telescope is a special purpose Optical telescope used to observe the Sun. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. These telescopes use filtration and projection techniques for direct observation, in additional to filtered cameras of various types. Specialized tools such as spectroscopes and spectrohelioscopes are used to examine sunspots and areas of sunspots. A spectrometer is an Optical instrument used to measure properties of Light over a specific portion of the Electromagnetic spectrum, typically used A spectrohelioscope is a Telescope designed to show the Sun in a particular Wavelength of light 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, through binoculars or a telescope is extremely dangerous, amateur observation of sunspots with the unaided eye is generally done by projection or via using proper filtration. Small sections of very dark filter glass, such as a #14 welder's glass is sometimes employed. An optical filter is a device which selectively transmits light having certain properties (often a particular range of Wavelengths that is range of Colours The eyepiece of a telescope is also used in the role of a "projector" to project the image, without filtration, on to a white screen where it can be viewed indirectly, and even traced, so sunspot evolution can be followed. Special purpose hydrogen-alpha narrow bandpass filters as well as aluminum coated glass attenuation filters (which have the appearance of mirrors due to their extremely high optical density) are also used on the front of a telescope to provide safe direct observation through the eyepiece. In Physics and Astronomy, H-alpha, also written Hα, is a specific Emission line created by Hydrogen at 6562 Vacuum deposition or vacuum coating is a family of processes used to deposit layers atom-by-atom or molecule-by-molecule at sub- Atmospheric pressure ( Vacuum In Optics, density is a unitless measure of the Transmittance of an optical element for a given length at a given Wavelength λ:

Application

A large group of sunspots in year 2004. The grey area around the spots can be seen very clearly, as well as the granulation of the sun's surface.

Due to their link to other kinds of solar activity, sunspots can be used to predict the space weather and with it the state of the ionosphere. Space weather is the concept of changing environmental conditions in Outer space. The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation Thus, sunspots can help predict conditions of short-wave radio propagation or satellite communications. Shortwave Radio operates between the frequencies of 3000 KHz (3 Radio propagation is a term used to explain how Radio waves behave when they are Transmitted, or are propagated from one point on the Earth A communications satellite (sometimes abbreviated to comsat) is an artificial Satellite stationed in space for the purposes of Telecommunications.

Don Easterbrook, a Professor Emeritus of geology at Western Washington University, has claimed that there is a cause-and-effect relationship between sunspot activity and global temperatures on Earth. Western Washington University ( WWU or Western) is one of six state-funded, four-year universities of Higher education in the It is also believed that sunspot activity has a direct effect on weather and climate change on the planet, the controversy over global warming has put scientists in opposition to each other, until more is known about the effects of sunspots and solar radiation levels and their exact relationship with Earth and its weather patterns (including temperature change) we must accept that there may be a correlation between global warming and sunspot activity. Global warming is the increase in the average measured temperature of the The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. [2]

Starspots on other stars

Periodic changes in brightness had been first seen on red dwarfs and in 1947 G. According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool Star, of the Main sequence, either late K E. Kron proposed that spots were the cause. ^[2] Since the mid 1990s observations of starspots have been made using increasingly powerful techniques yielding more and more detail: photometry determined starspot regions grew and decayed and showed cyclic behaviour similar to the Sun's; spectroscopy examined the structure of starspot regions; 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. Photometry is a technique of Astronomy concerned with measuring the Flux, or intensity of an Astronomical object 's Electromagnetic Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ Inhomogeneous structures on stellar surfaces ie temperature differences chemical composition or magnetic fields, create characteristic distortions in the spectral lines due to the 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 3500 kelvin, together with a warm spot of 4800 kelvin. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic ^[2][9]

Gallery

Please remember observing sunspots at sunsets without proper solar filters may permanently damage your eyes.

Sunspot 923 at sunset and in solar scope

Sunset Superior Mirage of sunspot #930

See also

• List of solar cycles
• Solar Rotation
• space weather
• radio propagation

References

External links

• Solar Cycle 24 and VHF Aurora Website (www.solarcycle24.com)
• Belgium World Data Center for the sunspot index
• High resolution sunspot image
• Sunspot images in high-res Impressive collection of sunspot images
• http://www.tvweather.com/awpage/history_of_the_atmosphere.htm
• NOAA Solar Cycle Progression: Current solar cycle.
  • Current conditions: Space weather
• 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
  • Propfire - displays current sunspot number in browser status bar
  • HamLinks Toolbar - displays solar flux, A Index and K Index data in a toolbar

Sunspot data

• 11,000 Year Sunspot Number Reconstruction. Space weather is the concept of changing environmental conditions in Outer space. Global Change Master Directory. Retrieved on 11 March 2005.
  • Unusual activity of the Sun during recent decades compared to the previous 11,000 years. WDC for Paleoclimatology. Retrieved on 11 March 2005.
• Sunspot Numbers from Ancient Times to Present from NOAA/NGDC. Global Change Master Directory. Retrieved on 11 March 2005.
  • SUNSPOT NUMBERS. NOAA NGDC Solar Data Services. Retrieved on 11 March 2005.
    • International Sunspot Number -- sunspot 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 1944-present
    • Ancient sunspot data 165 BC to 1684 AD
    • Group Sunspot Numbers (Doug Hoyt re-evaluation) 1610-1995