Solar phenomena

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Solar phenomena are

These phenomena are believed to be generated by a helical dynamo, located near the center of the Sun's mass, which generates strong magnetic fields, as well as a chaotic dynamo, located near the surface, which generates smaller magnetic field fluctuations.^[2] All solar fluctuations together are referred to as solar variation, producing space weather within the Sun's gravitational field.

Solar activity and related events have been recorded since the eighth century BCE. Throughout history, observation technology and methodology advanced, and in the 20th century, interest in astrophysics surged and many solar telescopes were constructed. The 1931 invention of the coronagraph allowed the corona to be studied in full daylight.

The Sun is a star located at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma and magnetic fields.^[3][4] It has a diameter of about 1,392,684 kilometres (865,374 mi),^[5] around 109 times that of Earth, and its mass (1.989×10³⁰ kilograms, approximately 330,000 times that of Earth) accounts for some 99.86% of the total mass of the Solar System.^[6] Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The remaining 1.69% (equal to 5,600 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon and iron.^[7]

The Sun formed about 4.567 billion

The Sun is a

Many solar phenomena change periodically over an average interval of about 11 years. This solar cycle affects

The solar cycle also modulates the flux of short-wavelength solar radiation, from ultraviolet to X-ray and influences the frequency of solar flares, coronal mass ejections and other solar eruptive phenomena.

Part of a series of articles about
Heliophysics
Heliospheric current sheet
Heliosphere Sun Solar System Space climate Space weather
Fundamentals Plasma Flux tube Magnetic reconnection Particle acceleration Nuclear physics
Interplanetary medium IMF Parker spiral Solar wind Cosmic ray ICME Forbush decrease
Magnetospherics History Particle motion Magnetosheath Plasmasphere Van Allen radiation belt Ring current Birkeland current Magnetic storm Aurora GIC Dst Substorm Space tornado Space hurricane Polar wind Flux transfer event
Solar phenomena Solar cycle max min Solar storm Coronal hole CME Solar prominence Solar flare Solar particle event Radio emission
v t e

A coronal mass ejection (CME) is a massive burst of

A solar flare is a sudden flash of brightness observed over the Sun's surface or the

• A solar flare
• 
  On August 31, 2012, a long prominence/filament of solar material that had been hovering in the Sun's atmosphere, the corona, erupted out into space at 4:36 p.m. EDT.
• 
  Diagram of the magnetic-field structure of a solar flare and its origin, inferred to result from the deformation of such a magnetic structure linking the solar interior with the solar atmosphere up through the

  corona

  .
• 
  A complete 2D-Image taken by STEREO (High Resolution)

A solar proton event (SPE), or "proton storm", occurs when particles (mostly protons) emitted by the Sun become accelerated either close to the Sun during a flare or in interplanetary space by CME shocks. The events can include other nuclei such as helium ions and

A prominence is a large, bright, gaseous feature extending outward from the

A typical prominence extends over many thousands of kilometers; the largest on record was estimated at over 800,000 kilometres (500,000 mi) long [24] – roughly the solar radius.

When a prominence is viewed against the Sun instead of space, it appears darker than the background. This formation is called a solar filament.^[24] It is possible for a projection to be both a filament and a prominence. Some prominences are so powerful that they eject matter at speeds ranging from 600 km/s to more than 1000 km/s. Other prominences form huge loops or arching columns of glowing gases over sunspots that can reach heights of hundreds of thousands of kilometers.^[25]

Sunspots are relatively dark areas on the Sun's radiating 'surface' (photosphere) where intense magnetic activity inhibits convection and cools the Photosphere. Faculae are slightly brighter areas that form around sunspot groups as the flow of energy to the photosphere is re-established and both the normal flow and the sunspot-blocked energy elevate the radiating 'surface' temperature. Scientists began speculating on possible relationships between sunspots and solar luminosity in the 17th century.^[26][27] Luminosity decreases caused by sunspots (generally < - 0.3%) are correlated with increases (generally < + 0.05%) caused both by faculae that are associated with active regions as well as the magnetically active 'bright network'.^[28]

The net effect during periods of enhanced solar magnetic activity is increased radiant solar output because faculae are larger and persist longer than sunspots. Conversely, periods of lower solar magnetic activity and fewer sunspots (such as the Maunder Minimum) may correlate with times of lower irradiance.^[29]

Sunspot activity has been measured using the

Sunspots usually appear as pairs with opposite magnetic polarity.[31] Detailed observations reveal patterns, in yearly minima and maxima and in relative location. As each cycle proceeds, the latitude of spots declines, from 30 to 45° to around 7° after the solar maximum. This latitudinal change follows Spörer's law.

For a sunspot to be visible to the human eye it must be about 50,000 km in diameter, covering 2,000,000,000 square kilometres (770,000,000 sq mi) or 700 millionths of the visible area. Over recent cycles, approximately 100 sunspots or compact sunspot groups are visible from Earth.^[c][32]

Sunspots expand and contract as they move about and can travel at a few hundred meters per second when they first appear.

• 
  Spörer's law noted that at the start of an 11-year sunspot cycle, the spots appeared first at higher latitudes and later in progressively lower latitudes.
• 
  A report in the Daily Mail characterized sunspot 1302 as a "behemoth" unleashing huge solar flares.
• 
  Detail of the Sun's surface, analog photography with a 4" Refractor, yellow glass filter and foil filter ND 4, Observatory Großhadern, Munich
• 
  Detailed view of sunspot, 13 December 2006

The solar wind is a stream of plasma released from the Sun's upper atmosphere. It consists of mostly electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in density, temperature and speed over time and over solar longitude. These particles can escape the Sun's gravity because of their high energy.

The solar wind is divided into the slow solar wind and the fast solar wind. The slow solar wind has a velocity of about 400 kilometres per second (250 mi/s), a temperature of 2×10⁵ K and a composition that is a close match to the corona. The fast solar wind has a typical velocity of 750 km/s, a temperature of 8×10⁵ K and nearly matches the photosphere's.^[33][34] The slow solar wind is twice as dense and more variable in intensity than the fast solar wind. The slow wind has a more complex structure, with turbulent regions and large-scale organization.^[35][36]

Both the fast and slow solar winds can be interrupted by large, fast-moving bursts of plasma called interplanetary CMEs, or ICMEs. They cause shock waves in the thin plasma of the heliosphere, generating electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation that precede the CME.

Space weather is the environmental condition within the Solar System, including the solar wind. It is studied especially surrounding the Earth, including conditions from the magnetosphere to the ionosphere and thermosphere. Space weather is distinct from terrestrial weather of the troposphere and stratosphere. The term was not used until the 1990s. Prior to that time, such phenomena were considered to be part of physics or aeronomy.

Solar storms are caused by disturbances on the Sun, most often

An aurora is a natural light display in the sky, especially in the high latitude (Arctic and Antarctic) regions, in the form of a large circle around the pole. It is caused by the collision of solar wind and charged magnetospheric particles with the high altitude atmosphere (thermosphere).

Most auroras occur in a band known as the auroral zone,^[41][42] which is typically 3° to 6° wide in latitude and observed at 10° to 20° from the geomagnetic poles at all longitudes, but often most vividly around the spring and autumn equinoxes. The charged particles and solar wind are directed into the atmosphere by the Earth's magnetosphere. A geomagnetic storm expands the auroral zone to lower latitudes.

Auroras are associated with the solar wind. The Earth's magnetic field traps its particles, many of which travel toward the poles where they are accelerated toward Earth. Collisions between these ions and the atmosphere release energy in the form of auroras appearing in large circles around the poles. Auroras are more frequent and brighter during the solar cycle's intense phase when CMEs increase the intensity of the solar wind.^[43]

A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field. The increase in solar wind pressure compresses the magnetosphere and the solar wind's magnetic field interacts with the Earth's magnetic field to transfer increased energy into the magnetosphere. Both interactions increase plasma movement through the magnetosphere (driven by increased electric fields) and increase the electric current in the magnetosphere and ionosphere.^[44]

The disturbance in the interplanetary medium that drives a storm may be due to a CME or a high speed stream (co-rotating interaction region or CIR)

Several space weather phenomena are associated with geomagnetic storms. These include Solar Energetic Particle (SEP) events, geomagnetically induced currents (GIC), ionospheric disturbances that cause radio and radar scintillation, disruption of compass navigation and auroral displays at much lower latitudes than normal. A 1989 geomagnetic storm energized ground induced currents that disrupted electric power distribution throughout most of the province of Quebec^[46] and caused aurorae as far south as Texas.^[47]

A sudden ionospheric disturbance (SID) is an abnormally high ionization/plasma density in the

The production of

Solar activity and related events have been regularly recorded since the time of the

Babylonians. Early records described solar eclipses, the corona and sunspots.

Soon after the invention of telescopes, in the early 1600s, astronomers began observing the Sun. Thomas Harriot was the first to observe sunspots, in 1610. Observers confirmed the less-frequent sunspots and aurorae during the Maunder minimum.^[50] One of these observers was the renowned astronomer Johannes Hevelius who recorded a number of sunspots from 1653 to 1679 in the early Maunder minimum, listed in the book Machina Coelestis (1679).^[51]

Solar spectrometry began in 1817.

On 1 September 1859, Richard C. Carrington and separately R. Hodgson first observed a solar flare.[52] Carrington and Gustav Spörer discovered that the Sun exhibits differential rotation, and that the outer layer must be fluid.^[52]

In 1907–08, George Ellery Hale uncovered the Sun's magnetic cycle and the magnetic nature of sunspots. Hale and his colleagues later deduced Hale's polarity laws that described its magnetic field.^[52]

Bernard Lyot's 1931 invention of the coronagraph allowed the corona to be studied in full daylight.^[52]

The Sun was, until the 1990s, the only star whose surface had been resolved.^[53] Other major achievements included understanding of:^[54]

• X-ray-emitting loops (e.g., by Yohkoh)
• Corona and solar wind (e.g., by SoHO)
• Variance of solar brightness with level of activity, and verification of this effect in other solar-type stars (e.g., by
  ACRIM
  )
• The intense fibril state of the magnetic fields at the visible surface of a star like the Sun (e.g., by Hinode)
• The presence of magnetic fields of 0.5×10⁵ to 1×10⁵ gauss at the base of the conductive zone, presumably in some fibril form, inferred from the dynamics of rising azimuthal flux bundles.
• Low-level electron neutrino emission from the Sun's core.^[54]

In the later twentieth century, satellites began observing the Sun, providing many insights. For example, modulation of solar luminosity by magnetically active regions was confirmed by satellite measurements of total solar irradiance (TSI) by the ACRIM1 experiment on the Solar Maximum Mission (launched in 1980).^[28]

• Solar activity
  )
• Climate change (section Solar output)
• Outline of astronomy
• Radiative levitation
• Solar cycle