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A corona is the outermost layer of a star's atmosphere. It is a hot but relatively dim region of plasma populated by intermittent coronal structures known as solar prominences or filaments.
Sunspots are temporary spots on the Sun's surface that are darker than the surrounding area. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sunspots appear within active regions, usually in pairs of opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.
Tau Ceti, Latinized from τ Ceti, is a single star in the constellation Cetus that is spectrally similar to the Sun, although it has only about 78% of the Sun's mass. At a distance of just under 12 light-years from the Solar System, it is a relatively nearby star and the closest solitary G-class star. The star appears stable, with little stellar variation, and is metal-deficient relative to the Sun.
The Maunder Minimum, also known as the "prolonged sunspot minimum", was a period around 1645 to 1715 during which sunspots became exceedingly rare. During a 28-year period (1672–1699) within the minimum, observations revealed fewer than 50 sunspots. This contrasts with the typical 40,000–50,000 sunspots seen in modern times over a similar timespan.
A variable star is a star whose brightness as seen from Earth changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:
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 general much larger than those on the Sun: up to about 30% of the stellar surface may be covered, corresponding to starspots 100 times larger than those on the Sun.
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 surface. Over the period of a solar cycle, levels of solar radiation and ejection of solar material, the number and size of sunspots, solar flares, and coronal loops all exhibit a synchronized fluctuation from a period of minimum activity to a period of a maximum activity back to a period of minimum activity.
The Fraunhofer lines are a set of spectral absorption lines. They are dark absorption lines, seen in the optical spectrum of the Sun, and are formed when atoms in the solar atmosphere absorb light being emitted by the solar photosphere. The lines are named after German physicist Joseph von Fraunhofer, who observed them in 1814.
Edward Walter Maunder was an English astronomer. His study of sunspots and the solar magnetic cycle led to his identification of the period from 1645 to 1715 that is now known as the Maunder Minimum.
Richard Christopher Carrington was an English amateur astronomer whose 1859 astronomical observations demonstrated the existence of solar flares as well as suggesting their electrical influence upon the Earth and its aurorae; and whose 1863 records of sunspot observations revealed the differential rotation of the Sun.
Friederich Wilhelm Gustav Spörer was a German astronomer.
In solar physics, Spörer's law is an empirical law for the variation of heliographic latitudes at which solar active regions form 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.
John Allen "Jack" Eddy was an American astronomer. He studied historical sunspot records, and popularised the name Maunder Minimum for the sunspot minimum which occurred in the late 17th century.
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. The rate of surface rotation is observed to be the fastest at the equator and to decrease as latitude increases. The solar rotation period is 24.47 days at the equator and almost 38 days at the poles. The average rotation is 28 days.
The Spörer Minimum is a hypothesized 90-year span of low solar activity, from about 1460 until 1550, which was identified and named by John A. Eddy in a landmark 1976 paper published in Science titled "The Maunder Minimum". It occurred before sunspots had been directly observed and was discovered instead by analysis of the proportion of carbon-14 in tree rings, which is strongly correlated with solar activity. It is named for the German astronomer Gustav Spörer.
This is a timeline of astronomy. It covers ancient, medieval, Renaissance-era, and finally modern astronomy.
The Evershed effect, named after the British astronomer John Evershed, is the radial flow of gas across the photospheric surface of the penumbra of sunspots from the inner border with the umbra towards the outer edge.
PICARD is a satellite dedicated to the simultaneous measurement of the absolute total and spectral solar irradiance, the diameter and solar shape, and to the Sun's interior probing by the helioseismology method. These measurements obtained throughout the mission allow study of their variations as a function of solar activity. It launched, along with the Prisma spacecraft, on 15 June 2010 on a Dnepr launcher from Dombarovskiy Cosmodrome, near Yasny, Russia. The mission, originally planned for two years, ended on 4 April 2014.
Superflares are very strong explosions observed on stars with energies up to ten thousand times that of typical solar flares. The stars in this class satisfy conditions which should make them solar analogues, and would be expected to be stable over very long time scales. The original nine candidates were detected by a variety of methods. No systematic study was possible until the launch of the Kepler space telescope, which monitored a very large number of solar-type stars with very high accuracy for an extended period. This showed that a small proportion of stars had violent outbursts. In many cases there were multiple events on the same star. Younger stars were more likely to flare than old ones, but strong events were seen on stars as old as the Sun.
Solar observation is the scientific endeavor of studying the Sun and its behavior and relation to the Earth and the remainder of the Solar System. Deliberate solar observation began thousands of years ago. That initial era of direct observation gave way to telescopes in the 1600s followed by satellites in the twentieth century.