The dark centre of a sunspot is called as

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1 Science and the Universe: A Brief Tour • Introduction • 1.1 The Nature of Astronomy • 1.2 The Nature of Science • 1.3 The Laws of Nature • 1.4 Numbers in Astronomy • 1.5 Consequences of Light Travel Time • 1.6 A Tour of the Universe • 1.7 The Universe on the Large Scale • 1.8 The Universe of the Very Small • 1.9 A Conclusion and a Beginning • For Further Exploration • 3 Orbits and Gravity • Thinking Ahead • 3.1 The Laws of Planetary Motion • 3.2 Newton’s Great Synthesis • 3.3 Newton’s Universal Law of Gravitation • 3.4 Orbits in the Solar System • 3.5 Motions of Satellites and Spacecraft • 3.6 Gravity with More Than Two Bodies • Key Terms • Summary • For Further Exploration • Collaborative Group Activities • 4 Earth, Moon, and Sky • Thinking Ahead • 4.1 Earth and Sky • 4.2 The Seasons • 4.3 Keeping Time • 4.4 The Calendar • 4.5 Phases and Motions of the Moon • 4.6 Ocean Tides and the Moon • 4.7 Eclipses of the Sun and Moon • Key Terms • Summary • For Further Exploration • Collaborative Group Activities • 5 Radiation and Spectra • Thinking Ahead • 5.1 The Behavior of Light • 5.2 The Electromagnetic Spectrum • 5.3 Spectroscopy in Astronomy • 5.4 The Structure of the Atom • 5.5 Formation of Spectral Lines • 5.6 The Doppler Effect • Key Terms • Summary • For Further Exploration • Collaborative Group Activities • 6 Astronomical Instruments • Thinking Ahead • 6.1 Telescopes • 6.2 Telescopes Today • 6.3 Visible-Light Detectors and Instruments • 6.4 Radio Telescopes • 6.5 Observ...

• Biermann,L. Der gegenwärtige Stand der Theorie konvektiver Sonnenmodelle. Vierteljahrsch. Astron. Gesellsch. 76, 194–200 (1941). • Parker,E. N. The nature of the sunspot phenomenon. I. Solutions of the heat transport equation. Sol. Phys. 36, 249–274 (1974). • Thomas,J. H. & Weiss,N. O. in Sunspots: Theory and Observations (eds Thomas, J. H. & Weiss, N. O.) 3–59 (Kluwer, Dordrecht, 1992). • Spruit,H. C. Heat flow near obstacles in the solar convection zone. Sol. Phys. 55, 3–34 (1977). • Fowler,L. A., Foukal,P. & Duvall, T. Jr Sunspot bright rings and the thermal diffusivity of solar convection. Sol. Phys. 84, 33–44 (1983). • Neckel,H. & Labs,D. The solar radiation between 3300 and 12500 Å. Sol. Phys. 90, 205–258 (1984). • Spruit,H. C. The flow of heat near a starspot. Astron. Astrophys. 108, 356–360 (1982). • Fox,P. A., Sofia,S. & Chan,K. L. Convective flows around sunspot-like objects. Sol. Phys. 135, 15–42 (1991). • Brickhouse,N. S. & LaBonte,B. J. Mass and energy flow near sunspots I. Observations of moat properties. Sol. Phys. 115, 43–60 (1988). • Kuhn,J. R., Lin,H. & Loranz,D. Gain calibrating nonuniform image-array data using only the image data. Publ. Astron. Soc. Pacif. 103, 1097–1108 (1991). • Skumanich,A. & Lites,B. W. Stokes profile analysis and vector magnetic fields. I. Inversion of photospheric lines. Astrophys. J. 322, 473–482 (1987). • Lites,B. W., Rutten,R. J. & Berger,T. E. Dynamics of the solar chromosphere. II. CaII H2V and K2V grains versus internetwo...

The sun is a great ball of fiery, electrically charged gas. As the sun advances through its regular 11-year solar cycle, electromagnetic activity on the star's surface gets more and more chaotic. This turbulence inevitably leads to the appearance of sunspots — dark, planet-size regions that form in the sun's lower atmosphere as a result of intense magnetic disturbances. The two massive sunspot groups open on the northeast limb of the sun. (Image credit: Langkawi National Observatory, MYSA/MOSTI) The reason sunspots appear so much darker than the rest of the sun's visible surface, or photosphere, is because they are much cooler, and the gas underneath a sunspot emits about 25% as much light as the rest of the sun, according to NASA. Sunspots are still scorching hot — astronomers estimate that the temperature of a typical one is about 6,300 degrees Fahrenheit (3,500 degrees Celsius) — but the surrounding photosphere blazes at roughly 10,000 F (5,500 C), according to the National Weather Service ( NWS). Sunspots are cool because they form in regions where magnetic fields are especially strong — roughly 2,500 times stronger than Earth's, and far stronger than anywhere else on the sun, according to the NWS. This increases the magnetic pressure exerted on sunspots, thereby inhibiting the flow of heat from the sun's interior to the surface and leaving the region cooler than its surroundings. The pent-up magnetic energy of sunspots can have some spectacular — and dangerous — side ...

\( \newcommand\) • • • • • • Learning Objectives By the end of this section, you will be able to: • Describe the sunspot cycle and, more generally, the solar cycle • Explain how magnetism is the source of solar activity Before the invention of the telescope, the Sun was thought to be an unchanging and perfect sphere. We now know that the Sun is in a perpetual state of change: its surface is a seething, bubbling cauldron of hot gas. Areas that are darker and cooler than the rest of the surface come and go. Vast plumes of gas erupt into the chromosphere and corona. Occasionally, there are even giant explosions on the Sun that send enormous streamers of charged particles and energy hurtling toward Earth. When they arrive, these can cause power outages and other serious effects on our planet. Sunspots The first evidence that the Sun changes came from studies of sunspots, which are large, dark features seen on the surface of the Sun caused by increased magnetic activity. They look darker because the spots are typically at a temperature of about 3800 K, whereas the bright regions that surround them are at about 5800 K (Figure \(\PageIndex\) Sunspots Rotate Across Sun’s Surface. This sequence of photographs of the Sun’s surface tracks the movement of sunspots across the visible hemisphere of the Sun. On March 30, 2001, this group of sunspots extended across an area about 13 times the diameter of Earth. This region produced many flares and coronal mass ejections. The Sunspot Cycle...

Observe a close-up of a rotating sunspot Although the magnetic field Oscillations are observed in sunspots as well. When a section of the photosphere known as a light bridge crosses the umbra, rapid horizontal flow is seen. Although the umbral field is too strong to permit motion, rapid oscillations called umbral flashes appear in the chromosphere just above, with a 150-second period. In the chromosphere above the penumbra, so-called running waves are observed to travel radially outward with a 300-second period. The members of a spot pair are identified by their position in the pair with respect to the rotation of the Sun; one is designated as the leading spot and the other as the following spot. In a given hemisphere (north or south), all spot pairs typically have the same polar configuration—e.g., all leading spots may have northern polarity, while all following spots have southern polarity ( see below). A new spot group generally has the proper polarity configuration for the hemisphere in which it forms; if not, it usually dies out quickly. Occasionally, regions of reversed polarity survive to grow into large, highly active spot groups. An ensemble of sunspots, the surrounding bright chromosphere, and the associated strong magnetic field regions The emergence of a new spot group emphasizes the three-dimensional structure of the magnetic loop. First we see a small brightening (called an emerging flux region [EFR]) in the photosphere and a greater one in the chromosphere....

NASA/ Sunspots appear dark to us because they're cooler than the surrounding areas on the photosphere, which has a temperature of about 10,000 degrees Fahrenheit (5,537.8 degrees Celsius). The dark interior of a sunspot, called the umbra, is about 1,600 degrees cooler than the rest of the sun's surface. That interior is surrounded by a larger, lighter area called the penumbra, which is about 500 degrees cooler than the rest of the sun. Sunspots are cooler because they're areas of intense magnetism -- so intense that it inhibits the flow of hot gases from the sun's interior to its surface. Sunspots occur because the sun isn't a hunk of rock like the To an observer on Earth, sunspots appear to move because sun's surface itself is moving (though not in one piece, as we discussed). It takes the sun much longer to complete its rotation than the Earth does, but because the sun is 100 times larger than our planet, a sunspot looks like it's moving four times faster than a point on Earth. The average sunspot is as big as the Earth, but some are really, really huge. Scientists measure them by comparing them to the sun's visible area (that is, the half of the sun that we can see from Earth). The biggest recorded sunspot in the last century occurred in 1947. It covered 6,132 millionths of the sun's visible area -- roughly 18 times the Earth's surface area [source: In the next section, we'll analyze the sunspot cycle and what causes it.

By observing spots, English astronomer c. 1860) that the Sun rotates not as a solid body but differentially, fastest at the equator and slower at higher solar latitudes. Sunspots are never seen exactly at the equator or near the poles. Annie Russel Maunder in 1922 charted the latitude drift of spots during each solar cycle. Her chart is sometimes called the butterfly diagram because of the winglike shapes assumed by the graph. Each solar cycle begins with small spots appearing in middle latitudes of the Sun. Succeeding spots appear progressively closer to the Sun’s equator as the cycle reaches its maximum level of activity and declines. This article was most recently revised and updated by

Coronal Holes: The (Rarely Round) Gaps In The Sun's Atmosphere Scientists aren't sure exactly why holes form in the hot and glowing outermost layer of gas surrounding the sun. But one theory is that the dark blotches we see on images of the sun could be the remnants of the (relatively) cool splotches called sunspots. NASA's Solar Dynamics Observatory captured this picture of the sun on June 18. The dark blue area in the upper left quadrant of the sun is a huge coronal hole more than 400,000 miles across. Coronal holes are areas of the sun's outermost atmospheric layer — the corona — where the magnetic field opens up and solar material quickly flows out. NASA/SDO hide caption toggle caption NASA/SDO NASA's Solar Dynamics Observatory captured this picture of the sun on June 18. The dark blue area in the upper left quadrant of the sun is a huge coronal hole more than 400,000 miles across. Coronal holes are areas of the sun's outermost atmospheric layer — the corona — where the magnetic field opens up and solar material quickly flows out. NASA/SDO There's a hole in the sun's corona. But don't worry — that happens from time to time. "A coronal hole is just a big, dark blotch that we see on the sun in our images," says That's because you have to look at wavelengths of light that the human eye can't see. As the name suggests, coronal holes are holes in the sun's corona, not the sun itself. The corona is a hot and glowing outer layer of atmosphere that surrounds the sun. It extend...

The sun is a great ball of fiery, electrically charged gas. As the sun advances through its regular 11-year solar cycle, electromagnetic activity on the star's surface gets more and more chaotic. This turbulence inevitably leads to the appearance of sunspots — dark, planet-size regions that form in the sun's lower atmosphere as a result of intense magnetic disturbances. The two massive sunspot groups open on the northeast limb of the sun. (Image credit: Langkawi National Observatory, MYSA/MOSTI) The reason sunspots appear so much darker than the rest of the sun's visible surface, or photosphere, is because they are much cooler, and the gas underneath a sunspot emits about 25% as much light as the rest of the sun, according to NASA. Sunspots are still scorching hot — astronomers estimate that the temperature of a typical one is about 6,300 degrees Fahrenheit (3,500 degrees Celsius) — but the surrounding photosphere blazes at roughly 10,000 F (5,500 C), according to the National Weather Service ( NWS). Sunspots are cool because they form in regions where magnetic fields are especially strong — roughly 2,500 times stronger than Earth's, and far stronger than anywhere else on the sun, according to the NWS. This increases the magnetic pressure exerted on sunspots, thereby inhibiting the flow of heat from the sun's interior to the surface and leaving the region cooler than its surroundings. The pent-up magnetic energy of sunspots can have some spectacular — and dangerous — side ...