PHYSICS SEMINAR PRESENTATION SUNSPOTS 1 Sunspot Introduction to Sun Spots Our Star Has Spots! The sun is a great star to study; since it is so close we can see many more details than on any other star. One of the details we see are sunspots, small dark regions on the surface of the sun. When we watch every day for years, we can see that sunspots come and go in patterns or cycles. The so-called "sunspot cycle" not only affects the sun, it also affects life here on Earth. Does it surprise you that our sun has spots? These spots may be seen even without a telescope. They look like dark spots or blemishes on the sun's surface. If you took a picture of the sunspots each day, you would notice that they all move a little bit every day. The sunspots do not really move, that small daily movement is caused by the sun turning on its axis. The sun spins on its axis once every 27 days just as the Earth spins once every 24 hours. We do not know for sure what causes sunspots, but scientists know two things. Each sunspot has a magnetic field that is strongest near the center of the sunspot. They also know that a sunspot is cooler than the rest of the sun; the surface of the sun is about 6000 degrees C and a sunspot may be as cool as 3,000 degrees C. Sunspots follow some interesting patterns on our star. There is a cycle of Spots; during an eleven year period, the number of spots seen on the sun Starts near zero and increases each year until many spots can be seen at Once. Then the number of sunspots decreases slowly each year until there are very few sunspots again. The pattern keeps repeating every eleven ears. Although some cycles have more sunspots than other cycles, the Pattern does not change. The year 2000 had many sunspots because it is the peak of the current 11 year cycles. Parts of the Sun by Fraser Cain on March 11, 2012
Transcript
PHYSICS SEMINAR PRESENTATION
SUNSPOTS
1
Sunspot
Introduction to Sun
Spots
Our Star Has Spots! The sun is a great star to study; since it is so close we can see many more
details than on any other star. One of the details we see are sunspots, small dark regions on the
surface of the sun. When we watch every day for years, we can see that sunspots come and go in
patterns or cycles. The so-called "sunspot cycle" not only affects the sun, it also affects life here on
Earth.
Does it surprise you that our sun has spots? These spots may be seen even without a telescope.
They look like dark spots or blemishes on the sun's surface. If you took a picture of the sunspots
each day, you would notice that they all move a little bit every day. The sunspots do not really
move, that small daily movement is caused by the sun turning on its axis. The sun spins on its axis
once every 27 days just as the Earth spins once every 24 hours. We do not know for sure what
causes sunspots, but scientists know two things. Each sunspot has a magnetic field that is strongest
near the center of the sunspot. They also know that a sunspot is cooler than the rest of the sun; the
surface of the sun is about 6000 degrees C and a sunspot may be as cool as 3,000 degrees C.
Sunspots follow some interesting patterns on our star. There is a cycle of Spots; during an eleven
year period, the number of spots seen on the sun Starts near zero and increases each year until
many spots can be seen at Once. Then the number of sunspots decreases slowly each year until
there are very few sunspots again. The pattern keeps repeating every eleven ears. Although some
cycles have more sunspots than other cycles, the Pattern does not change. The year 2000 had
many sunspots because it is the peak of the current 11 year cycles.
Parts of the Sunby Fraser Cain on March 11, 2012
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Interior of the Sun. Image credit: NASA
From here on Earth, the Sun like a smooth ball of fire, and before the discovery of sunspots by Galileo, astronomers even thought it was a perfect orb with no imperfections. However, we now know that the Sun, like Earth, is actually made up of several layers, each of which serves its own purpose. It’s this structure of the Sun that powers this massive furnace and provider of all terrestrial life and energy.
What is the Sun Made Of?If you could take the Sun apart, and stack up its various elements, you would find that the Sun is made of hydrogen (74%) and helium (about 24%). Astronomers consider anything heavier than helium to be a metal.
The remaining amount of the Sun is made of iron, nickel, oxygen, silicon, sulfur, magnesium, carbon, neon, calcium and chromium. In fact, the Sun is 1% oxygen; and everything else comes out of that last 1%.
Supernova remnant SNR 0509-67.5. Supernovae provided the heavier elements in the Sun. Image credit: NASA/ESA/CXC
Where did these elements come from? The hydrogen and helium came from the Big Bang. In the early moments of the Universe, the first element, hydrogen, formed from the soup of elementary particles. The pressure and temperatures were still so intense that the entire Universe had the same conditions as the core of a star. Hydrogen was fused into helium until the Universe cooled down enough that this reaction couldn’t happen any more. The ratios of hydrogen and helium that we see in the Universe today were created in those first few moments after the Big Bang.
The other elements were created in other stars. Stars are constantly fusing hydrogen into helium in their cores. Once the hydrogen in the core runs out, they switch to fusing heavier and heavier elements, like helium, lithium, oxygen. Most of the heavier metals we see in the Sun were formed in other stars at the end of their lives.
The heaviest elements, like gold and uranium, were formed when stars many times more massive that our Sun detonated in supernova explosions. In a fraction of a second, as a black hole was forming, elements were crushed together in the intense heat and pressure to form the heaviest elements. The explosion scattered these elements across the
region, where they could contribute to the formation of new stars.
Our Sun is made up of elements left over from the Big Bang, elements formed from dying stars, and elements created in supernovae. That’s pretty amazing.
The proton-proton chain that fuels nuclear fusion inside the core of our Sun. Credit: Ian O'Neill
Layers of the SunAlthough the Sun is mostly just a ball of hydrogen and helium, it’s actually broken up into distinct layers. The layers of the Sun are created because the temperatures and pressures increase as you move towards the center of the Sun. The hydrogen and helium behave differently under the changing conditions.
The Core of the SunLet’s start at the innermost layer of the Sun, the core of the Sun. This is the very center of the Sun, where temperatures and pressures are so high that fusion can happen. The Sun is combining hydrogen into helium atoms, and this reaction gives off the light and heat that we see here on Earth. The density of the core is 150 times the density of water, and the temperatures are thought to be 13,600,000 degrees Kelvin.
Astronomers believe that the core of the Sun extends from the center out to about 0.2 solar radius. And within this region, temperatures and pressures are so high that hydrogen atoms are torn apart to form separate protons, neutrons and electrons. With all of these free floating particles, the Sun is able to reform them into atoms of helium.
This reaction is exothermic. That means that the reaction gives off a tremendous amount of heat – 3.89 x 1033 ergs of energy every second. The light pressure of all this energy streaming from the core of the Sun is what stops it from collapsing inward on itself.
Massive coronal mass ejection on. This image shows the size of the Earth to scale. NASA / SDO / J. Major.
The Radiative ZoneThe radiative zone of the Sun starts at the edge of the core of the Sun (0.2 solar radii), and extends up to about 0.7 radii. Within the radiative zone, the solar material is hot and dense enough that thermal radiation transfers the heat of the core outward through the Sun.
The core of the Sun is where nuclear fusion reactions are happening – protons are merged together to create atoms of helium. This reaction produces a tremendous amount of gamma radiation. These photons of energy are emitted, absorbed, and then emitted again by various particles in the radiative zone.
The path that photons take is called the “random walk”. Instead of going in a straight beam of light, they travel in a zigzag direction, eventually reaching the surface of the Sun. In fact, it can take a single photon upwards of 200,000 years to make the journey through the radiative zone of the Sun. As they transfer from particle to particle, the photons lose energy. That’s a good thing, since we wouldn’t want only gamma radiation streaming from the Sun. Once these photons reach space, they take a mere 8 minutes to get to Earth.
Most stars will have radiative zones, but their size depends on the star’s size. Small stars will have much smaller radiative zones, and the
convective zone will take up a larger portion of the star’s interior. The smallest stars might not have a radiative zone at all, with the convective zone reaching all the way down to the core. The largest stars would have the opposite situation, where the radiative zone reaches all the way up to the surface.
The Convective ZoneOutside the radiative zone is another layer, called the convective zone, where heat from inside the Sun is carried up by columns of hot gas.
Most stars have a convective zone. In the case of the Sun, it starts at around 70% of the Sun’s radius and goes to the outer surface (the photosphere). Gas deeper inside the star is heated up so that it rises, like globs of wax in a lava lamp. As it gets to the surface, the gas loses some of its heat, cools down, and sinks back towards the center to pick up more heat. Another example would be a pot of boiling water on the stove.
Solar Prominence and Sunspot 1271. Credit: John Chumack
The surface of the Sun looks granulated. These granules are the columns of hot gas that carry heat to the surface. They can be more than 1,000 km across, and typically last about 8 to 20 minutes before dissipating.
Astronomers think that low mass stars, like red dwarfs, have a convective zone that goes all the way down to the core. Unlike the Sun, they don’t have a radiative zone at all.
The PhotosphereThe layer of the Sun that we can see from Earth is called the photosphere. Below the photosphere, the Sun becomes opaque to visible light, and astronomers have to use other methods to probe its interior. The
temperature of the photosphere is about 6,000 Kelvin, and gives off the yellow-white light that we see.
Above the photosphere is the atmosphere of the Sun. Perhaps the most dramatic of these is the corona, which is visible during a total solar eclipse.
Diagram of the Sun. Image credit: NASA
Diagram of the SunThis is a diagram of the Sun, originally developed by NASA for educational purposes.
Visible, IR and UV radiation – The light that we see coming from the Sun is visible, but if you close your eyes and just feel the warmth, that’s IR, or infrared radiation. And the light that gives you a sunburn is ultraviolet (UV) radiation. The Sun produces all of these wavelengths at the same time.
Photosphere 6000 K – The photosphere is the surface of the Sun. This is the region where light from the interior finally reaches space. The temperature is 6000 K, which is the same as 5,700 degrees C.
Radio emissions – In addition to visible, IR and UV, the Sun also gives off radio emissions, which can be detected by a radio telescope. These emissions rise and fall depending on the number of sunspots on the surface of the Sun.
Coronal Hole – These are regions on the Sun where the corona is cooler, darker and has less dense plasma.
2100000 – This is the temperature of the Sun’s radiative zone. Convective zone/Turbulent convection – This is the region of the Sun where
heat from the core is transferred through convection. Warm columns of plasma rise to the surface in columns, release their heat and then fall back down to heat up again.
Coronal loops – These are loops of plasma in the Sun’s atmosphere that follows magnetic flux lines. They look like big arches, stretching up from the surface of the Sun for hundreds of thousands of kilometers.
Core – The is the heart of the Sun, where the temperatures and pressures are so high that nuclear fusion reactions can happen. All of the energy coming from the Sun originates from the core.
14500000 K – The temperature of the core of the Sun. Radiative Zone – The region of the Sun where energy can only be
transferred through radiation. It can take a single photon 200,000 years to get from the core, through the radiative zone, out to the surface and into space.
Neutrinos – Neutrinos are nearly mass-less particles blasted out from the Sun as part of the fusion reactions. There are millions of neutrinos passing through your body every second, but they don’t interact, so you can’t feel them.
Chromospheric Flare – The Sun’s magnetic field can get twisted up and then snap into a different configuration. When this happens, there can be powerful X-ray flares emanating from the surface of the Sun.
Magnetic Field Loop – The Sun’s magnetic field extends out above its surface, and can be seen because hot plasma in the atmosphere follows the field lines.
Spot – A sunspot. These are areas on the Sun’s surface where the magnetic field lines pierce the surface of the Sun, and they’re relatively cooler than the surrounding areas.
Prominence – A bright feature that extends above the surface of the Sun, often in the shape of a loop.
Energetic particles – There can be energetic particles blasting off the surface of the Sun to create the solar wind. In solar storms, energetic protons can be accelerated to nearly the speed of light.
X-rays – In addition to the wavelengths we can see, there are invisible X-rays coming from the Sun, especially during flares. The Earth’s atmosphere protects us from this radiation.
Bright spots and short-lived magnetic regions – The surface of the Sun has many brighter and dimmer spots caused by changing temperature. The temperature changes from the constantly shifting magnetic field.
During the minimum of the sunspot cycle, when there are few spots on the sun, most of the spots are located near the sun's north andsouth poles. During the maximum of the sunspot cycle, when there are lots of spots on the sun, most of the spots are located closer to the sun's equator. When scientists make a graph of sunspots and where they are located during different parts of the 11-year cycle ,the pattern is beautiful. The graph looks like a butterfly! Something else interesting happens to the sun during the eleven year cycle. The earth has two magnetic poles, the north pole and the south pole. The sun also has two magnetic poles. At the end of each cycle, the magnetic poles on the sun change! The pole that was
negative becomes positive; the pole that was positive become negative. Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature. Like magnets, they also have two poles. Although they are at temperatures of roughly 3000–4500 K (2727–4227 °C), the contrast with the surrounding material at about 5780 K (5500 °C) leaves them clearly visible as dark spots, as the luminous intensity of a heated black body (closely approximated by the photosphere) is a function of temperature to the fourth power. If the sunspot were isolated from the surrounding photosphere it would be brighter than an electric arc. Sunspots expand and contract as they move across the surface of the Sun and can be as large as 80,000 kilometers (50,000 mi) in diameter, making the larger ones visible from Earth without the aid of a telescope.[1] They may also travel at relative speeds ("proper motions") of a few hundred m/s when they first emerge onto the solar photosphere.
Manifesting intense magnetic activity, sunspots host secondary phenomena such as coronal loops (prominences) and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on stars are commonly called starspots and both light and dark spots have been measured.[2]
Almost any picture you see of the Sun will show sunspots. These are dark dots on the surface of the Sun, and they’re even visible from Earth without a telescope. Galileo was the first to point a telescope at the Sun and see sunspots, but it wasn’t until recently that astronomers had a good explanation for what causes them.
Although sun spots are darker than the surrounding regions of the Sun, they’re actually incredibly hot. A sun spot can be more than 3,500 degrees Kelvin. Even though that would be white hot if you could look at it, that’s less bright than the average surface temperature of the Sun, which is 5,800 Kelvin. They’re still extremely hot, but this is enough of a temperature difference that they look dark in comparison. These features can be so large that the Earth could fit within an average-sized sunspot.
The Sun is mostly made of plasma, a state of matter which has the additional property of being highly magnetic. Because of the movement of plasma inside the Sun, it generates a powerful magnetic field, similar to the Earth’s magnetosphere. But the magnetic field on the Sun is constantly shifting around. Physicists believe that these magnetic field lines can get so twisted up that they curl up like a rubber band and pierce the outside of the Sun.
Sunspots are created at the points where the Sun’s magnetic field lines pierce through the Sun’s photosphere (the part of the Sun that we can see). Although they look dark, they’re really just a few thousand degrees cooler than the surrounding photosphere, so they’re actually still very hot. The magnetic field lines are loops, so the sunspots appear in pairs; the two points where a single loop comes out of the Sun and then goes back in.
A sunspot can be broken into two parts: the central umbra and the surrounding penumbra. From within the central umbra region, the magnetic field lines are perpendicular to the Sun’s surface, and are roughly vertical. Within the penumbral region, the field lines are inclined at an angle.
Coronal mass ejections are explosions on the surface of the Sun that can through out enormous amounts of material. They usually blast out of regions dominated by sunspots.
Astronomers have been tracking the number of sunspots for more than
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100 years, and they’ve learned that the number of sunspots on the Sun’s surface rises and falls in an 11-year cycle. At the low point of the cycle, called the solar minimum, there can be few or no sunspots on the surface of the Sun. And then at the high point, the solar maximum, we see the highest number of sunspots.
Spots on the sun were once seen as rare and exotic, but are now a commonplace, solar event.
ISSUE #52: SUNSPOTS FROM A TO B - SOLAR MAGNETISM
Figure 1: Closeup of a sunspot taken with the Swedish Solar Telescope in La Palma, the Cannary Islands. ( Courtesy:
Göran B. Scharmer, and Boris V. Gudiksen, The Swedish Institute for Solar Physics)
Sunspots have been observed on the sun for thousands of years, but only during the last century have
astronomers figured out what they actually are, and why the sun has them! Most of this advancement in our
knowledge occurred because of the advent of new technologies to observe the sun since the 1850s. Another
important clue to solving the sunspot mystery was revealed when scientists developed powerful new insights
about how matter and the various fundamental forces of nature, actually worked.
Sunspots are found in the photosphere of the sun, where the temperature is 6,000 C, and the surface is
covered by innumerable, small convection cells called 'granules' (Figure 1). Sunspots have a dark, central
region called the umbra, surrounded by a lighter region called the penumbra. When examined at high
resolution, the penumbral region resolves into numerous filaments or 'fibrils' that radiate outwards from the dark
umbral zone (Figure 2). Temperatures in the umbral zone are commonly about 2,200 C, while in the penumbral
zone, temperatures can be as high as 3,500 C. The reason that sunspots appear dark is that they are as much
as 3,000 C cooler than the rest of the solar surface! Because brightness depends on the fourth-power of the
temperature, the sunspot umbra emits 1/6 as much light as a similar-sized piece of the solar surface.
concentrated into dense rope-like structures. These magnetic ropes become buoyant and float up to the
surface, where they erupt as a pair of sunspots; one with a north-type polarity and one with a south-type. At the
start of the first cycle, the leading sunspot has the same polarity as the magnetic field of the sun in that
hemisphere. When the next 11-year cycle starts, the leading sunspot has the opposite polarity. Then during the
third cycle, the polarity of the leading sunspot has returned to the same polarity as the solar field in that
hemisphere. The full 'Hale-Cycle' takes 22 years.
The magnetic properties of sunspots were discovered by astronomer George Ellery Hale (1868-1938), in 1908
using a new instrument he had invented, and a newly-discovered physical effect called Zeeman splitting. Under
laboratory conditions, if you look at the light from atoms in a strong magnetic field, a very high resolution
spectroscope will show that the atomic lines are split into pairs. The wavelength separation of these pairs will
increase as the strength of the magnetic field increases. After careful measurements, Hale was able to
determine that sunspots have magnetic fields as strong as 1,500 Gauss, which is about 2000 times Earth's
magnetic field, and 100 times the Sun's common surface field!
The discovery of strong sunspot fields also provided astronomers with a powerful clue as to why they are dark.
The strong magnetic field of a spot makes it very hard for gases below these spots to transport heat from the
lower layers of the sun to its surface. That means that the gases can be considerably cooler than the rest of the
sun because there is less energy available from below to keep them heated. As a result, the gases are cooler,
emit less light, and are darker.
Recently, data obtained by the SOHO satellite has allowed astronomers to look below the surface of a sunspot!
The accompanying animation, based on a computer model of the physical conditions, reveals just how gases
move around. (SOHOconv.mpeg). As the cooler umbral gasses flow downwards, they collide with upward-
moving gases, and are deflected around the spot.
An important consequence of this flow pattern is that the energy flowing from lower regions is diverted around
the sunspot and causes the surrounding solar surface to emit more ultraviolet light. As a result, during sunspot
maximum conditions, the sun is actually a few percent BRIGHTER in ultraviolet light than at other times, even
though the surface is visibly covered with lots of dark umbral regions. This UV increase can be detected at
Earth, and actually produces a measurable climate impact!
By the way, high-resolution images of sunspots reveal new details that challenge astronomers to understand
even finer details of sunspot physics. In Figure 1, taken with the Swedish Vacuum Telescope at La Palma in the
Canary Islands, features described as hairs and canals are seen as dark cores visible within the bright
filaments that extend into the sunspot. The filaments' newly revealed dark cores are seen to be thousands of
kilometers long but only about 100 kilometers wide. These features represent previously unknown and
unexplored solar phenomena.
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Sunspot Cycle
An Active Sunspot
Galileo Galilei made a huge number of revolutionary discoveries when he pointed
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his first rudimentary telescope at the skies in 1610. One of these was the discovery that the Sun isn’t a pristine ball, but actually had blemishes that moved across its surface. Galileo was the first to discover sunspots.
From this point on, astronomers were hard at work cataloging the size and number of sunspots, and they learned that the rise and fall in the number of sunspots follows an 11-year period – this is the sunspot cycle.
Astronomers now maintain the “sunspot number”. They add up the total number of sunspot groups, and the count the number of individual sunspots. And these observations have been made for over 300 years. Sometimes the sunspot cycle can be as short as 9 years and other times as long as 14 years. But on average, it takes 11 years.
At the height of solar activity, there can be dozens of sunspots on the surface of the Sun at the same time, and at the lowest points, the Sun can go days without sunspots. When the Sun is most active, it releases more flares and coronal mass ejections, so astronomers are continuing to gather data about the sunspot cycle, to better predict solar weather. This will be especially important when the first astronauts travel to the Moon, and could be at risk to a radioactive solar storm.
Why does the sunspot cycle rise and fall like this? Scientists just aren’t sure. It’s all connected to the Sun’s magnetic field, which twists and turns as it rotates. Sunspots occur at the points where the magnetic field lines pierce the surface of the Sun.
But why it takes 11-years between minimum and maximum? Nobody knows. One theory is that it has something to do with the tidal interactions between the Sun, Jupiter and Saturn.
Here’s an article from Universe Today about a puzzling lack of sunspots, andanother article about how the Sun burst into light during a cycle.
Here’s a page from NASA that explains the sunspot cycle, and a bunch of charts from NOAA.
A sunspot viewed close-up in ultraviolet light, taken by the TRACE spacecraftMain article: Solar cycle
Although the details of sunspot generation are still a matter of research, it appears that sunspots are the visible counterparts of magnetic flux tubes in the Sun's convective zone that get "wound up" by differential rotation. If the stress on the tubes reaches a certain limit, they curl up like a rubber band and puncture the Sun's surface. Convection is inhibited at the puncture points; the energy flux from the Sun's interior decreases; and with it surface temperature.
The Wilson effect tells us that sunspots are actually depressions on the Sun's surface. Observations using the Zeeman effect show that prototypical sunspots come in pairs with opposite magnetic polarity. 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 (normal to the Sun's surface).
The surrounding penumbra, which is lighter, where the magnetic field is more inclined.
Magnetic pressure should tend to remove field concentrations, causing the sunspots to disperse, but sunspot lifetimes are measured in days or even weeks. Recent observations from the Solar and Heliospheric Observatory (SOHO) using sound waves traveling below the Sun's photosphere (local helioseismology) have been used to develop a three-dimensional image of the internal structure below sunspots; these observations show that there is a powerful downdraft underneath each sunspot, forming a rotating vortex that concentrates the magnetic field. Sunspots can thus be thought of as self-perpetuating storms, analogous in some ways to terrestrial hurricanes.
Butterfly diagram showing paired Spörer's law behavior
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. Early in the cycle, sunspots appear in the higher latitudes and then move towards the equator as the cycle approaches maximum: this is called Spörer's law.
Wolf number sunspot index displays various periods, 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.
The modern understanding of sunspots starts with George Ellery Hale, who first linked magnetic fields and sunspots in 1908.[14] 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 that magnetic fields cause the behavior described by Spörer's law, as well as other effects, which are twisted by the Sun's rotation.
Sunspot populations quickly rise and more slowly fall on an irregular cycle of 11 years, although significant variations in the number of sunspots attending 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.[24] Over the last decades the Sun has had a markedly high average level of sunspot activity; it was last similarly active over 8,000 years ago.[6]
The number of sunspots correlates with the intensity of solar radiation over the period since 1979, when satellite measurements of absolute radiative flux became 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 brighter than the average, and so are hotter; 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).[25][26] Sunspots were rarely observed during the Maunder Minimum in the second part of the 17th century (approximately from 1645 to 1715).
The Swedish 1-m Solar Telescope at Roque de los Muchachos Observatory, La Palma in the Canary Islands
Sunspots are observed with land-based and Earth-orbiting solar telescopes. These telescopes use filtration and projection techniques for direct observation, in addition to various types of filtered cameras. Specialized tools such as spectroscopes and spectrohelioscopes are used to examine sunspots and sunspot areas. 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 permanently damages vision, amateur observation of sunspots is generally conducted indirectly using projected images, or directly through protective filters. Small sections of very dark filter glass, such as a #14 welder's glass are effective. A telescope eyepiece can project the image, without filtration, onto a white screen where it can be viewed indirectly, and even traced, to follow sunspot evolution. 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) on the front of a telescope provide safe observation through the eyepiece.
A large group of sunspots in 2004. The grey area around the spots can be seen very clearly, as well as the granulation of the Sun's surface
Due to its link to other kinds of solar activity, sunspot occurrence can be used to help predict space weather, the state of the ionosphere, and hence the conditions of short-wave radio propagation or satellite communications. Solar activity (and the sunspot cycle) are frequently discussed in the context of global warming; Jack Eddy noted the apparent correlation between the Maunder Minimum of sunspot occurrence and the Little Ice Age in European climate.[citation
needed] Sunspots themselves, in terms of the magnitude of their radiant-energy deficit, have only a weak effect on the terrestrial climate[27] in a direct sense. On longer time scales, such as the solar cycle, other magnetic phenomena (faculae and the chromospheric network) do correlate with sunspot occurrence. It is these other features that make the solar constant increase slightly at sunspot maxima, when naively one might expect that sunspots would make it decrease.[28]
British economist William Stanley Jevons suggested in the 1870s that there is a relationship between sunspots and business cycle crises. Jevons reasoned that sunspots affect Earth's weather, which, in turn, influences crops and, therefore, the economy.[29]
Spots on other stars
In 1947, G. E. Kron proposed that starspots were the reason for periodic changes in brightness on red dwarfs.[2] Since the mid-1990s, starspot observations have been made using increasingly powerful techniques yielding more and more detail: photometry showed starspot growth and decay and showed cyclic behavior similar to the Sun's; spectroscopy examined the structure of starspot regions by analyzing variations in spectral line splitting due to the Zeeman Effect; 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. 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 3,500 K (3,230 °C), together with a warm spot of 4,800 K (4,530 °C).[2][30]
This is a picture of the Sun captured by NASA’s SOHO spacecraft. It would be a typical day on the Sun, except for the enormous coronal mass ejection blasting out of the upper right-hand side of the Sun. When the Sun is at its most active state, it can release 5-6 of these a day.
This photograph of the Sun was one of the first captured by NASA’s STEREO mission. These twin spacecraft were launched in 2006. One is leading the Earth in orbit, while the other has fallen behind. With both observing the Sun, scientists are given a 3-dimensional view of the Sun.
This pic of the Sun shows our star on a calm day, believe it or now. When you look close, this is what the surface of the Sun is doing all the time. The TRACE spacecraft was launched in 1997, and helps scientists study the Sun’s magnetic field – and to take beautiful photos like this.
This picture of the Sun was captured by the EIT instrument on board the NASA/ESA SOHO spacecraft. It reveals the normally invisible ultraviolet radiation streaming from the Sun. It’s actually a composite of three different Sun photos captured at different parts of the ultraviolet spectrum and then merged together.
You’re going to need a set of 3-D glasses to get the most out of this Sun photograph. It’s an image of Sun captured by NASA’s twin STEREO spacecraft. Images like this help scientists understand how the Sun interacts with its local environment, and better predict space weather.
For a better video playback experience we recommend a html5 video browser.Sunspot NOAA 875.
For a better video playback experience we recommend a html5 video browser.A flare from sunspot NOAA 875.
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This visualization tracks the emergence and evolution of a sunspot group as seen starting in early February 2011 and continuing for two weeks. Images are sampled one hour apart. The camera tracks the movement of the solar rotation. At this scale, a 'shimmer' of the solar surface is visible, created by the turnover of convection cells.
A view of the coronal structure .
September 201
A view of the coronal structure above a different sunspot seen in October 2010.
