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Sunspot

A sunspot is a region on the Sun Sun

|+ The Sun   |+ |- ... 

's surface that is marked by a lower temperature than its surroundings and intense magnetic Magnetism

In physics [i], magnetism is one of the phenomena [i] by which materials [i] exert an attractive or repu ... 

 activity, which inhibits convection Convection

Convection is the transfer of potential energy, for example heat [i], by currents within liquids and gas ... 

, forming areas of low surface temperature. Although they are blindingly bright, at temperatures of roughly 4000-4500 K Kelvin

The Kelvin scale is a temperature [i] scale where absolute zero [i]—the coldest possible temperatu ... 

, the contrast with the surrounding material at some 5700 K leaves them clearly visible as dark spots. If they were isolated from the surrounding photosphere they would be brighter than an electric arc Electric arc

An electric arc is an electrical breakdown [i] of a gas which produces an ongoing plasma [i] discharge [i] ... 

. As of 2006, we are near a minimum in the sunspot cycle Solar variation

Solar variations are fluctuations in the amount of energy emitted by the Sun [i]. ... 

 .

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Timeline

1610   Johannes Fabricius is the first to observe sunspots by telescope Telescope

The word "telescope" usually refers to optical telescope [i]s, but there are telescopes for most of the ... 

.

1611   Johannes and David Fabricius discover sunspots.

1645   Beginning of the Maunder Minimum Maunder Minimum

The Maunder Minimum is the name given to the period roughly from 1645 [i] to 1715 [i] A.D., when sunspot [i] ... 

, a time period when sunspots became exceedingly rare



Encyclopedia

A sunspot is a region on the Sun Sun

|+ The Sun   |+
|-
... 

's surface that is marked by a lower temperature than its surroundings and intense magnetic Magnetism

In physics [i], magnetism is one of the phenomena [i] by which materials [i] exert an attractive or repu ... 

 activity, which inhibits convection Convection

Convection is the transfer of potential energy, for example heat [i], by currents within liquids and gas ... 

, forming areas of low surface temperature. Although they are blindingly bright, at temperatures of roughly 4000-4500 K Kelvin

The Kelvin scale is a temperature [i] scale where absolute zero [i]—the coldest possible temperatu ... 

, the contrast with the surrounding material at some 5700 K leaves them clearly visible as dark spots. If they were isolated from the surrounding photosphere they would be brighter than an electric arc Electric arc

An electric arc is an electrical breakdown [i] of a gas which produces an ongoing plasma [i] discharge [i] ... 

. As of 2006, we are near a minimum in the sunspot cycle Solar variation

Solar variations are fluctuations in the amount of energy emitted by the Sun [i]. ... 

 .

Similar phenomenon observed on stars other than the Sun is commonly called a starspot.


Sunspot variation





Sunspot numbers have been recorded since 1700 AD and estimated back to 11,000 BP. The recent trend is upward from 1900 to the 1960s, then somewhat downward . The Sun was last similarly active over 8,000 years ago.

The number of sunspots has been found to correlate with the intensity of solar radiation Solar radiation

Solar radiation is radiant energy [i] emitted by the sun [i], particularly electromagnetic energy.... 

 over the period - since 1979 - when satellite measurements of radiation are available. Since sunspots are dark it is natural to assume that more sunspots means less solar radiation . However, the surrounding areas are brighter and the overall effect is that more sunspots means a brighter sun. The variation is small and was only established once satellite measurements of solar variation Solar variation

Solar variations are fluctuations in the amount of energy emitted by the Sun [i]. ... 

 became available in the 1980s.

During the Maunder Minimum Maunder Minimum

The Maunder Minimum is the name given to the period roughly from 1645 [i] to 1715 [i] A.D., when sunspot [i]... 

 there were hardly any sunspots at all and the earth may have cooled by up to 1°C Celsius

The Celsius scale is a temperature [i] scale named after the Swedish [i] astronomer Anders Celsius [i] ... 

.

History

Apparent references to sunspots were made by Chinese astronomers in 28 BC , 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. A large sunspot was also seen in the time of Charlemagne Charlemagne

Charlemagne was the King of the Franks [i] who conquered Italy [i] and took the Iron Crown of Lombardy [i]... 

, though the observation was misinterpreted until Galileo Galileo Galilei

Galileo Galilei was an Italian [i] physicist [i], astronomer [i], astrologer [i] and philosopher [i] ... 

 gave the correct explanation in 1612.

They were first observed telescopically in late 1610 by Frisian astronomers Johannes and David Fabricius, who published a description in June 1611. 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. 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 Solar System

The Solar System or solar system is the stellar system [i] comprising the Sun [i] and ... 

. They showed that the Sun rotated, and their comings and goings showed that the Sun changed, contrary to the teaching of Aristotle Aristotle

Aristotle was an ancient Greek [i] philosopher [i], a student of Plato [i] ... 

. The details of their apparent motion could not be readily explained except in the heliocentric Heliocentrism

In astronomy [i], heliocentrism is the theory [i] that the Sun [i] is at the center of the Universe [i]... 

 system of Copernicus Nicolaus Copernicus

Nicolaus Copernicus was an astronomer [i] who provided the first modern formulation of a heliocentric [i] ... 

.

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. 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.

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. The economist William Stanley Jevons William Stanley Jevons

William Stanley Jevons, English [i] economist [i] and logician [i], was born in Liverpool [i]. ... 

 suggested that there is a relationship between sunspots and crises in business cycles. 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. 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 Aurora (astronomy)

The aurora is a bright glow observed in the night sky, usually in the polar zone.... 

, which were also absent at the same time. Even the lack of a solar corona Corona

In astronomy, a corona is the luminous plasma [i] "atmosphere [i]" o ... 

 during solar eclipse Solar eclipse

A solar eclipse occurs when the Moon [i] passes between Earth [i] and the Sun [i], thereby totally or pa ... 

s was noted prior to 1715.

Sunspot research was dormant for much of the 17th and early 18th centuries because of the Maunder Minimum Maunder Minimum

The Maunder Minimum is the name given to the period roughly from 1645 [i] to 1715 [i] A.D., when sunspot [i]... 

, 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.

;Significant events
An extremely powerful flare was emitted toward Earth on 1 September 1859. It interrupted telegraph service and caused visible Aurora Borealis Aurora (astronomy)

The aurora is a bright glow observed in the night sky, usually in the polar zone.... 

 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. 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



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. 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. This model is supported by observations using the Zeeman effect Zeeman effect

The Zeeman effect is the splitting of a spectral line [i] into several components in the presence of a magnetic field [i] ... 

 that show that prototypical sunspots come in pairs with opposite magnetic polarity. From cycle to cycle, the polarities of leading and trailing sunspots change from north/south to south/north and back. Sunspots usually appear in groups.

The sunspot itself can be divided into two parts:
  • umbra Umbra

    The umbra is the darkest part of a shadow.... 

  • penumbra Penumbra

    The penumbra is that part of the shadow where the light source is only partially blocked.... 




Magnetic field Magnetic field

In physics [i], a magnetic field is that part of the electromagnetic field [i] that exists when there is ... 

 lines would ordinarily repel each other, causing sunspots to disperse rapidly, but sunspot lifetime is about two weeks. Recent observations from the Solar and Heliospheric Observatory Solar and Heliospheric Observatory

The Solar and Heliospheric Observatory is a spacecraft [i] that was launched on 2 December [i] 1995 [i] ... 

  using sound waves travelling 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 Vortex

A vortex is a spinning, often turbulent [i], flow with closed streamline [i]s. ... 

 that concentrates magnetic field lines. Sunspots are self-perpetuating storms, similar in some ways to terrestrial hurricane Tropical cyclone

In meteorology [i], a tropical cyclone is a storm system fueled by the heat released when moist air rise ... 

s.



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

Sprer's law predicts the variation of sunspot [i] latitudes during a solar cycle [i]. ... 

.

Today it is known that there are various periods in the Wolf number Wolf number

The Wolf number is a quantity which measures the number of sunspots [i] and groups of sunspots present o ... 

 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 Solar variation

Solar variations are fluctuations in the amount of energy emitted by the Sun [i]. ... 

 and is deeply linked to a variation in the solar magnetic field that changes polarity with this period, too.

A modern understanding of sunspots starts with George Ellery Hale, in which magnetic fields and sunspots are linked. 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 Babcock Model

The Babcock Model describes a mechanism which can explain magnetic and sunspot [i] patterns observed on ... 

 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.

Application

Sunspots are relatively easily observed; a small telescope with a projection facility suffices. In some circumstances sunspots can be observed with the naked eye. Small plates of a dark glass normally used for welding are also available, which can be used to view the sun by blocking out most of its light. These are very inexpensive, and enable you to clearly see much of the solar activity going on during any clear day. .

Due to their link to other kinds of solar activity, they can be used to predict the space weather Space weather

Space weather is the concept of changing environmental conditions in outer space [i]. ... 

 and with it the state of the ionosphere Ionosphere

he ionosphere is the part of the atmosphere [i] that is ionized [i] by solar radiatio... 

. Thus, sunspots can help predict conditions of radio short-wave propagation or satellite communications.






External links

  • Impressive collection of sunspot images
  • : Current solar cycle.
    • Current conditions: Space weather Space weather

      Space weather is the concept of changing environmental conditions in outer space [i]. ... 

  • by William James Sidis

Sunspot data

      • 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 1610-1995