Sunspots: Modern Research 4 of 7 The Sunspot Cycle Cycles have been around In the last few decades, we've started to understand the forces behind sunspots, but we've known for over a 150 years that sunspots appear in cycles. The average number of visible sunspots varies over time, increasing and decreasing on a regular cycle of between 9.5 to 11 years, on average about 10.8 years. An amateur astronomer named Heinrich Schwabe, was the first to note this cycle, in 1843. The part of the cycle with low sunspot activity is referred to as " solar minimum " while the portion of the cycle with high activity is known as " solar maximum ." In fact they go around twice By studying the sun's magnetic field, modern astronomers have discovered that the cycle covers twenty-two years, with each eleven-year cycle of sunspots followed by a reversal of the direction of the Sun's magnetic field. According to Fisher, "the overall magnetic field structure changes in a way that is very interesting. It turns out that if the magnetic fields primarily point from west to east in the Northern Hemisphere (of the sun), they point from east to west in the Southern Hemisphere.

In the next eleven-year cycle, the fields are reversed. So the cycle is really twenty-two years." Migration Sunspots appear mostly in the low latitudes near the solar equator. In fact they almost never appear closer than 5 or further than 40 degrees latitude, north or south. As each sunspot cycle progresses, the sunspots gradually start to appear closer and closer to the equator. The sunspot locations for the most recent 11-year cycle are shown in this "butterfly" diagram." The locations "migrated" toward the equator (0 latitude) from both hemispheres throughout this half of the cycle. Do sunspots affect earth's climate? From 1645 to 1715, there was a drastically reduced number of sunspots. This period of reduced solar activity, which was first noticed by G. Spörer, was later investigated by E.W. Maunder, is now called the Maunder Minimum . That the same period of time was also unusually cold on Earth.

Similar periods of low solar activity seem to have occurred during the Spörer Minimum (1420-1530), the Wolf Minimum (1280-1340), and the Oort minimum (1010-1050). This succession of low-temperature periods is now called the "Little Ice Age," and the corresponding pattern of extreme sunspot minima has led to speculation that sunspot activity may affect the earth's climate. NASA/Marshall Solar Physics The Sunspot Cycle (Updated 2016/10/06) Please note: Dr. David Hathaway, a member of the MSFC solar physics group for 29 years, has transferred to NASA's Ames Research Center in California. Dr. Hathaway will continue to update his solar cycle pages. Dr. Hathaway's email address remains the same. Click on image for larger version. Sunspot Numbers In 1610, shortly after viewing the sun with his new telescope, Galileo Galilei (or was it Thomas Harriot?) made the first European observations of Sunspots .

Continuous daily observations were started at the Zurich Observatory in 1849 and earlier observations have been used to extend the records back to 1610. The sunspot number is calculated by first counting the number of sunspot groups and then the number of individual sunspots. The "sunspot number" is then given by the sum of the number of individual sunspots and ten times the number of groups. Since most sunspot groups have, on average, about ten spots, this formula for counting sunspots gives reliable numbers even when the observing conditions are less than ideal and small spots are hard to see. Monthly averages (updated monthly) of the sunspot numbers (181 kb JPEG image), (307 kb pdf-file), (62 kb text file) show that the number of sunspots visible on the sun waxes and wanes with an approximate 11-year cycle. (Note: there are actually at least two "official" sunspot numbers reported. The International Sunspot Number as compiled by the Solar Influences Data Analysis Center in Belgium, has been revised recently (V2.0 -- summer 2015), and should now more closely match the NOAA sunspot number.

The NOAA sunspot number is compiled by the US National Oceanic and Atmospheric Administration . The numbers tabulated in SN_m_tot_V2.0.txt are the monthly averages of the daily sunspot number with error estimates as posted at the WDC-SILSO, Royal Observatory of Belgium, Brussels.) The Maunder Minimum Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715 (38 kb JPEG image) . Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past. The connection between solar activity and terrestrial climate is an area of on-going research. The Butterfly Diagram Click on image for larger version. Detailed observations of sunspots have been obtained by the Royal Greenwich Observatory since 1874.

These observations include information on the sizes and positions of sunspots as well as their numbers. These data show that sunspots do not appear at random over the surface of the sun but are concentrated in two latitude bands on either side of the equator. A butterfly diagram (142 kb GIF image) (184 kb pdf-file) (updated monthly) showing the positions of the spots for each rotation of the sun since May 1874 shows that these bands first form at mid-latitudes, widen, and then move toward the equator as each cycle progresses. The Greenwich Sunspot Data The Royal Greenwich Observatory data has been appended with data obtained by the US Air Force Solar Optical Observing Network since 1977. This newer data has been reformatted to conform to the older Greenwich data and both are available in a local directory of ASCII files. Each file contains records for a given year with individual records providing information on the daily observations of active regions. Sunspot Cycle Predictions Click on image for larger version. MSFC Solar Physics Branch members Wilson, Hathaway, and Reichmann have studied the sunspot record for characteristic behavior that might help in predicting future sunspot activity.

Our current predictions of solar activity for the next few years can be found at this link . Although sunspots themselves produce only minor effects on solar emissions, the magnetic activity that accompanies the sunspots can produce dramatic changes in the ultraviolet and soft x-ray emission levels. These changes over the solar cycle have important consequences for the Earth's upper atmosphere. Sunspot Cycle Review Articles Sunspots, Solar Cycles, and the Little Ice Age – One Minute Astronomer Sunspots, Solar Cycles, and the Little Ice Age September 16, 2009 by Brian Ventrudo In the mid 19th-century, after many years of diligent solar observation, the German astronomer Samuel Schwabe noticed the number of sunspots visible on the sun’s disk rises and falls in nearly regular 11-year cycle. In peak years of the cycle, he found, there were spots visible on the sun most days, and hundreds of spots and groups of spots during the course of a year. In lean years, roughly 5.5 years after the peak, there were weeks or months when astronomers saw not a single sunspot, with fewer than a dozen spots observed during the year.

This regular cycle was traced back to the earliest telescopic observation of the sun in the 1600’s, and has been recorded in increasing detail by modern astronomers right up to the present day. (The diagram below shows a measure of the sunspot number over time since the 17th century. The 11-year period is clearly visible). The number of sunspots over time since the year 1600. On average the number of spots varies with an 11-year period What’s even more interesting is where the sunspots occur on the solar disk. As the number of sunspots rises from a minimum, the spots appear north and south of the solar equator, usually in the mid solar latitudes around 40 degrees. As the cycle continues, sunspots appear closer to the equator until at the next minimum, most spots appear in a narrow band at the equator. Then, it all starts over again. A plot of the position of sunspot position over time, shown below, is called the Maunder diagram or the “Butterfly Diagram”.

The solar “Butterfly Diagram”, which shows the solar latitude of new sunspot groups over time in a number of solar cycles This periodic change in the number and position of sunspots was a striking discovery. And it’s not just the number of sunspots that varies every 11 years. The sunspot cycle also matches up with other activity on the sun, including violent mass ejections, the size and extent of the outer reaches of the sun called the corona, and the intensity of light and charged particles the sun blasts out into space to affect the atmospheres and magnetic fields of many planets in the solar system, especially Earth. This near-regular 11-year variation in sunspots and other solar activity is called the solar cycle. It seems to be but a symptom of a complex and dimly understood dynamic process inside the sun called a “solar dynamo” that generates the sun’s global magnetic field. To make matters even stranger, the magnetic field seems to flip its polarity once every two sunspot cycles, or 22 years, which means the magnetic polarity of the sunspot pairs on the solar disk flips direction from cycle to cycle.

Right now, we’re coming out of a period of minimum sunspot activity, when very few sunspots were seen. The last cycle was labeled Cycle 23, and it peaked in mid-2000. The next is Cycle 24. (By convention, the sunspot cycle that began in the years 1755-56 is called Cycle 1). However, Cycle 24 has been slow to get started… there have been far fewer sunspots than expected. Many astronomers expect we’ll see many more sunspots in this cycle quite soon. But others suspect we’re due for a period of relatively few sunspots. It’s happened before, as you can see in the first diagram above. The period from 1645-1715, for example, had a sudden and unexplained disappearance of sunspots. The time is called the Maunder Minimum, and it coincided almost exactly with a chilly period in our climatic history called the “Little Ice Age”. Is it a coincidence the Maunder Minimum overlapped with the Little Ice Age? Perhaps not!

The effect of sunspots and solar activity on Earth’s atmosphere and climate will be the subject of our next article in this series on the sun. The Sunspot Cycle - Windows to the Universe RSS Feeds The Sunspot Cycle These two pictures of the Sun show how the number of sunspots changes. The picture on the left was taken near solar max in March 2001. It shows many sunspots. The picture on the right was taken near solar min in January 2005. It doesn't have any sunspots in it at all! Click on image for full size (62K JPEG) Images courtesy SOHO/NASA/ESA. This graph shows the number of sunspots counted each year for many years. Can you see how the number of sunspots changes? Can you see the 11-year sunspot cycle? Click on image for full size (8K GIF) Windows to the Universe original artwork by Randy Russell. The number of sunspots seen on the " surface " of the Sun changes from year to year. This rise and fall in sunspot counts is a cycle . The length of the cycle is about eleven years on average.

The Sunspot Cycle was discovered in 1843 by the amateur German astronomer Samuel Heinrich Schwabe. A peak in the sunspot count is called "solar maximum" (or "solar max"). The time when few sunspots appear is called a "solar minimum" (or "solar min"). An example of a recent sunspot cycle spans the years from the solar min in 1986, when 13 sunspots were seen, through the solar max in 1989 when more than 157 sunspots appeared, on to the next solar min in 1996 (ten years after the 1986 solar min) when the sunspot count had fallen back down to fewer than 9. The length of the sunspot cycle is, on average, around eleven years. But the length of the cycle does vary. Between 1700 and today, the sunspot cycle (from one solar min to the next solar min) has varied in length from as short as nine years to as long as fourteen years. Sometimes it is hard to get an exact count of number of sunspots on the Sun.

Some spots are much bigger than others, some sunspots cross together at their edges, and many spots appear in groups. In 1848, a Swiss astronomer named Rudolf Wolf came up with the best way to count sunspots. The sunspot count using Wolf's formula, now known as the Wolf sunspot number, is still in use today. Wolf used data from earlier astronomers to reconstruct sunspot counts as far back as the 1755-1766 cycle, which he dubbed "cycle 1". Since then, subsequent cycles have been numbered consecutively, so the cycle that began with the 1996 solar minimum is cycle 23. The Sunspot Cycle The Sunspot Cycle References Abstract Dark, highly magnetized features known as sunspots which regularly appear on the Sun�s surface have been observed and recorded by civilizations for thousands of years. The development of the telescope in the early 17th century ushered in a new age of sunspot observations and paved the way for a nearly continuous record of spot activity for the last 400 years.

The past few centuries have led to the progression of standards for observing sunspots and record keeping, as well as led to a greater understanding of the phenomenon. Contemporary research is focused on the forces which drive the 22-year solar cycle, composed of two 11-year sunspot cycles, and the possible effects these occurrences may be having on the Earth. Predicting the number of sunspots likely to occur during any given cycle has become critical to scientists concerned with understanding terrestrial consequences of solar activity and many methods have been created, combined and refined in attempt to predict sunspot activity. Definition of Sunspot Sunspots typically appear as a relatively small, dark and pore-like feature on the surface or 'photosphere' of the sun. The average size of a sunspot, when it first appears, is approximately 1600 kilometers in diameter (1000 miles) and the feature usually lasts for a few hours. Some sunspots, however, continue to grow and quickly become many times larger than the Earth and can last for more than a month. The sunspots which continue to grow and become the largest typically occur in pairs surrounded by several smaller spots.

A black region, called an "umbra" (meaning shadow) is found at the center of all sunspots and is encircled or rimmed by a lighter region called the "penumbra" (meaning almost shadow). In relation to the rest of the photosphere, sunspots are approximately 1500 degrees (K) cooler. This temperature difference gives the appearance of dark spots (cooler) on the sun's surface. Another characteristic of sunspots is their highly magnetized nature. When sunspots occur in pairs, each has an opposite magnetic pole and the north-south relationship developed by any given pair will be identical to all other sunspots located within the same hemisphere. Conversely, all sunspots in the opposite hemisphere will have the same magnetic relationship to each other, but opposite the relationship of those in the other hemisphere. (Tarbuck and Lutgens 2003). Image 1.5: Grouping of sunspots. Image courtesy of SOHO@NASA Image 4: Maunder Minimum. Courtesy of NASA Predictions The Sun is currently in Sunspot Cycle 24 which began on January 4th 2008.

Cycle 24 is expected to reach a sunspot maximum of 89 in May of 2013. Original predictions for cycle 24 had placed the number of spots below the exceptionally low 1907 number of 64.2 (cycle 14). Despite the recent modification (increase) of the projected sunspot number due to increased solar activity, 89 would still be the smallest number of spots in over 80 years. Several methods exist for predicting the behavior of the sunspot cycle. Typically, behavior and numbers of spots are easier to predict once the new cycle is underway. Predictions have proven most accurate approximately 3 years following the sunspot minimum (Hathaway et al. 1994). Techniques for predicting sunspot activity are normally designed around the time near and before sunspot minimums and emphasize the relationships between: 1) the length of the previous cycle; 2) level of activity at sunspot minimum; and 3) size of the previous cycle, all in relation to size of the next cycle maximum. Building and extrapolating on years of this type of modeling has allowed scientists and researchers to make extremely reliable predictions.

The time near and before sunspot minimums are crucial for developing the most reliable prediction methods. During this time, changes in the Earth�s electromagnetic field due to solar storms are recorded and compared against sunspot activity. Currently, a strong connection is suspected between solar storms, the Earth�s electromagnetic field and subsequent sunspot activity but the exact relationship is unknown. Various techniques surrounding the geomagnetic fluctuations caused by solar storms have been developed to predict subsequent sunspot activity. Among these techniques, three are widely used and include: 1) developing an index to determine the value of geomagnetic fields at sunspot minimum which correlates to the geomagnetic field during the ensuing maximum; 2) developing a geomagnetic index which has one component in phase and proportion to the sunspot number and another component which remains as the signal and occurs as a magnetic maximum near the sunspot minimum; 3) comparing the relationship between the number of days the Earth experiences geomagnetic disturbances from the sunspot cycle and the amplitude of the next sunspot maximum. Other researcher groups like NASA, have used averages obtained from combining some or all of the methods listed above (NASASP 2011). Image 5: Sunspot cycle 24 predictions.

Courtesy of NASA Conclusions Sunspots are dark, highly magnetized features which appear, develop and then disappear, near the mid-latitude and equatorial regions of the Sun�s surface or photosphere. Sunspot cycles occur in nearly regular intervals of 11 years and appear dark in relation to the rest of the sun because they are nearly 1500 degrees (K) cooler than surrounding regions. Rare and incomplete records of sunspot observations date as far back as 467 BCE, while regular record keeping began in the 17th century and has developed exponentially ever since. Sunspot cycles, which occur approximately every 11 years, are found within a larger solar cycle which refers to a 22-year solar magnetic polar reversal. Thus, two 11-year sunspot cycles occur within one solar cycle. Disruptions in the regular 11-year sunspot cycle have occurred during Earth�s history with the best example being that of the Maunder Minimum. During this time, which lasted from approximately 1645 to 1715, extremely low sunspot activity occurred.

This event coincided with what scientists refer to as the Little Ice Age, which led to ice age-like conditions for much of the North Atlantic and large portions of Europe. The Maunder Minimum has been a topic of much research and debate in various academic disciplines. While a correlation has been shown to exist between a decrease in sunspot activity and a resurgence of ice-age conditions for portions of the Earth in the past, research is on-going and in many cases speculative. In 2008 the 24th sunspot cycle began and with it came the usual predictions for spot numbers. Predictive methods have become increasingly complex, varied and more reliable with each passing cycle. The current cycle is predicted to peak with approximately 89 sunspots in May of 2013, though changes in solar activity may change this number as the cycle progresses. Related sites Sun Headed Into Hibernation, Solar Studies Predicts Captive Elephants Freed From a Life in Chains Three independent studies of the sun's insides, surface, and upper atmosphere all predict that the next solar cycle will be significantly delayed—if it happens at all. Normally, the next cycle would be expected to start roughly around 2020.

The combined data indicate that we may soon be headed into what's known as a grand minimum, a period of unusually low solar activity. The predicted solar "sleep" is being compared to the last grand minimum on record, which occurred between 1645 and 1715. Known as the Maunder Minimum, the roughly 70-year period coincided with the coldest spell of the Little Ice Age, when European canals regularly froze solid and Alpine glaciers encroached on mountain villages. (See "Sun Oddly Quiet—Hints at Next 'Little Ice Age?'" ) "We have some interesting hints that solar activity is associated with climate, but we don't understand the association," said Dean Pesnell , project scientist for NASA 's Solar Dynamics Observatory (SDO). Also, even if there is a climate link, Pesnell doesn't think another grand minimum is likely to trigger a cold snap. "With what's happening in current times—we've added considerable amounts of carbon dioxide and methane and other greenhouse gases to the atmosphere," said Pesnell, who wasn't involved in the suite of new sun studies.

"I don't think you'd see the same cooling effects today if the sun went into another Maunder Minimum-type behavior." Sunspots Losing Strength Sunspots are cool, dark blemishes visible on the sun's surface that indicate regions of intense magnetic activity. For centuries scientists have been using sunspots—some of which can be wider than Earth—to track the sun's magnetic highs and lows. (See the sharpest pictures yet of sunspots snapped in visible light .) For instance, 17th-century astronomers Galileo Galilei and Giovanni Cassini separately tracked sunspots and noticed a lack of activity during the Maunder Minimum. In the 1800s scientists recognized that sunspots come and go on a regular cycle that lasts about 11 years. We're now in Solar Cycle 24, heading for a maximum in the sun's activity sometime in 2013. Recently, the National Solar Observatory 's Matt Penn and colleagues analyzed more than 13 years of sunspot data collected at the McMath-Pierce Telescope at Kitt Peak, Arizona.

They noticed a long-term trend of sunspot weakening, and if the trend continues, the sun's magnetic field won't be strong enough to produce sunspots during Solar Cycle 25, Penn and colleagues predict. "The dark spots are getting brighter," Penn said today during a press briefing. Based on their data, the team predicts that, by the time it's over, the current solar cycle will have been "half as strong as Cycle 23, and the next cycle may have no sunspots at all." (Related: "Sunspot Cycles—Deciphering the Butterfly Pattern." ) Sun's "Jet Streams," Coronal Rush Also Sluggish Separately, the National Solar Observatory's Frank Hill and colleagues have been monitoring solar cycles via a technique called helioseismology. This method uses surface vibrations caused by acoustic waves inside the star to map interior structure. Specifically, Hill and colleagues have been tracking buried "jet streams" encircling the sun called torsional oscillations. These bands of flowing material first appear near the sun's poles and migrate toward the equator. The bands are thought to play a role in generating the sun's magnetic field.

(Related: "Sunspot Delay Due to Sluggish Solar 'Jet Stream?'" ) Sunspots tend to occur along the pathways of these subsurface bands, and the sun generally becomes more active as the bands near its equator, so they act as good indicators for the timing of solar cycles. "The torsional oscillation ... pattern for Solar Cycle 24 first appeared in 1997," Hill said today during the press briefing. "That means the flow for Cycle 25 should have appeared in 2008 or 2009, but it has not shown up yet." According to Hill, their data suggest that the start of Solar Cycle 25 may be delayed until 2022—about two years late—or the cycle may simply not happen. Adding to the evidence, Richard Altrock , manager of the U.S. Air Force's coronal research program for the National Solar Observatory (NSO), has observed telltale changes in a magnetic phenomenon in the sun's corona—its faint upper atmosphere.

Known as the rush to the poles, the rapid poleward movement of magnetic features in the corona has been linked to an increase in sunspot activity, with a solar cycle hitting its maximum around the time the features reach about 76 degrees latitude north and south of the sun's equator. The rush to the poles is also linked to the sun "sweeping away" the magnetic field associated with a given solar cycle, making way for a new magnetic field and a new round of sunspot activity. This time, however, the rush to the poles is more of a crawl, which means we could be headed toward a very weak solar maximum in 2013—and it may delay or even prevent the start of the next solar cycle. Quiet Sun Exciting for Science Taken together, the three lines of evidence strongly hint that Solar Cycle 25 may be a bust, the scientists said today during a meeting of the American Astronomical Society in Las Cruces, New Mexico. But a solar lull is no cause for alarm, NSO's Hill said: "It's happened before, and life seems to go on. I'm not concerned but excited." In many ways a lack of magnetic activity is a boon for science.

Strong solar storms can emit blasts of charged particles that interfere with radio communications, disrupt power grids, and can even put excess drag on orbiting satellites. "Drag is important for people like me at NASA," SDO's Pesnell said, "because we like to keep our satellites in space." What's more, a decrease in sunspots doesn't necessarily mean a drop in other solar features such as prominences, which can produce aurora -triggering coronal mass ejections. In fact, records show that auroras continued to appear on a regular basis even during the Maunder Minimum, Pesnell said. Solar Cycle Primer | NASA Solar Cycle Primer October 27, 2011 [image-52] Telescopes spotted the first blemish on the sun in 1611. While the sun had long been thought—at least in the Western world—to be an unchanging, "perfect" orb, sky-watchers observed black sunspots on the sun's surface that circled around as with the sun's rotation.

That first crack in the theory of the sun's immutable nature would soon fracture completely as the number of sunspots were shown to increase and decrease over time in a regular, approximately 11-year cycle, called the sunspot cycle. The exact length of the cycle can vary. It has been as short as eight years and as long as fourteen, but the number of sunspots always increases over time, and then returns to low again. [image-51] More sunspots mean increased solar activity, when great blooms of radiation known as solar flares or bursts of solar material known as coronal mass ejections (CMEs) shoot off the sun's surface. The highest number of sun spots in any given cycle is designated "solar maximum," while the lowest number is designated "solar minimum." Each cycle varies dramatically in intensity with some solar maxima being so low as to be almost indistinguishable from the preceding minimum. One such set of cycles famously occurred from 1645 to 1715 and is known as the Maunder Minimum. Those who watched the sun could count enough change in sunspot number that they could still track cycles, but the overall sunspot number dropped drastically.

One thirty-year period showed only 30 sunspots, one thousandth of what is typically seen. The timing of the Maunder Minimum corresponded to what's called the Little Ice Age in Europe—a time of colder weather, heavier snowfall and the freezing of unusually large bodies of water such as the Thames and even the Baltic Sea. The Little Ice Age lasted longer than the Maunder Minimum, and there are other potential causes. Nevertheless it is believed by many scientists that the prolonged solar minima and its corresponding decrease in solar energy cooled Earth. Mapping out the details of how much the change in solar energy could have produced such an effect remains an unresolved area of research. [image-36] It was not until the first half of the 20th century that scientists began to understand what causes the sunspot cycle. Researchers determined that the sunspots were a magnetic phenomenon and that, indeed, the entire sun was magnetized with a north and a south magnetic pole just like a bar magnet. The comparison to a simple bar magnet ends there, however, as the sun's interior is constantly on the move.

By tracking sound waves that course through the center of the sun, an area of research known as helioseismology, scientists can gain an understanding of what's deep inside the sun. They have found that the magnetic material inside the sun is constantly stretching, twisting, and crossing as it bubbles up to the surface. The exact pattern of movements is not conclusively mapped out, but over time they eventually lead to the poles reversing completely. The sunspot cycle happens because of this pole flip — north becomes south and south becomes north—approximately every 11 years. Some 11 years later, the poles reverse again back to where they started, making the full solar cycle actually a 22-year phenomenon. The sun behaves similarly over the course of each 11-year cycle no matter which pole is on top, however, so this shorter cycle tends to receive more attention. The sun is currently ramping up once again to solar maximum, so flares and CMEs are more common than they were a few years ago. This cycle may peak in late 2013, or early 2014, and should reach a minimum around 2020—although predictions about the sun's cycle are still quite uncertain.

This has been the slowest sunspot cycle of the space age, which is the time frame during which we have the most detailed observations. The slower-than-expected progress of this cycle has led some researchers to speculate that the next cycle might be even smaller, with few sunspots even at solar maximum. It is still far too early to know, but even if this is the case, it has happened before and isn't a cause for concern. Four hundred years of sunspot observations have shown that the cycle will always return. For more about sunspots, visit: Sunspots/Solar Cycle | NOAA / NWS Space Weather Prediction Center Sunspots/Solar Cycle Sunspots/Solar Cycle Sunspots are dark regions on the Sun. They are regions of intense magnetic field that are intimately associated with solar flares and coronal mass ejections. Sunspots appear dark on the sun’s surface because they are cooler (3700 K) than the rest of the solar surface (6000 K). Sunspots are cooler because their intense magnetic fields inhibit the rise of heat from the solar interior. Sunspots can appear alone, or in close connection to other sunspots.

Sunspots that are clearly connected to each other are grouped into active regions with an official number designated by NOAA. Active regions are classified according to their size and complexity with a scale known as the modified Zurich scale. Though sunspots appear darker than the rest of the sun to the naked eye, when the active regions they appear in are examined in ultraviolet or x-rays wavelengths, then sunspots and the associated active regions appear considerably brighter than the other areas of the Sun. The irradiance these other wavelengths show actually originates at higher levels in the solar atmosphere, but in the same region of the sun. The energy that sunspots lack in heat is made up instead by the energy of the magnetic field. The magnetic fields rise above the surface and remain strong, while the rest of the sun has weak overlying magnetic fields. The strong magnetic fields form into loops that confine solar plasma and heat it to extreme temperatures in excess of 1 million K. At these temperatures, we can’t see the plasma in visible light, but it becomes the dominant feature in ultraviolet and x-rays. Changes in these magnetic fields are the main source of most of space weather, like solar flares (Radio Blackouts) and fast coronal mass ejections (CMEs).

Sunspots change continuously, but individual spots may persist for only a few hours or for many weeks and even months. The total number of sunspots has long been known to vary with an 11-year period known as the solar cycle. The peak of the solar cycle is known as solar maximum and the valley of the cycle is known as solar minimum. At solar minimum there can be many days in a row with absolutely no sunspots visible, while at solar maximum hundreds of spots may be visible at any time. Solar cycles are numbered with solar cycle 1 beginning in 1755 and the most recent solar cycle, cycle 24, began in December, 2008. Counting of sunspot numbers is a bit tricky, because not only does each sunspot count as 1, but each active region counts as 10. Because a lone sunspot is also considered an active region, it is counted as 11, so on a given day, the sunspot number can be 0, 11, or any number greater than 11. Tags: Stanford SOLAR Center -- Ask A Solar Physicist FAQs - Answer How many sunspots are there on the sun? And how big are they?

This answer is courtesy of Dana Longcope, Montana State University. Roughly how many sunspots are on the Sun? There were 17 on a map made last Saturday, October 18, 1997. On other days, as many as 200 sunspots are visible, or else as few as zero. (More sunspots as the year 2000 approaches.) How big do they get? About 10,000 miles across for a medium-large sunspot. Often in science, simple questions can have complicated answers. This question is simple, but the answers are not simple for several reasons. The number of sunspots on the Sun is always changing. One reason for this is that a sunspot only lasts a week or two. A sunspot is "born" when a small piece of the Sun's surface suddenly grows dark, seemingly for no reason. (What has really happened is that underneath the surface a very strong magnetic field "turned on". We do not fully understand why this happens, but we have many good ideas.) After several weeks, the sunspot "breaks" into pieces and fades away. This is why we say a sunspot lasts only several weeks.

As the sunspot is "breaking up", the Sun is rotating about its axis, taking about 27 days to spin completely around. So even before a sunspot fades away, it might seem to disappear from view as it rotates around to the far side of the Sun. Other sunspots will come into view as they rotate onto the near side from the far side. If sunspots never changed, then in one month we would see all the sunspots there were, and then each month after that we would just see the same ones over and over again. But they do change, so each month we see different sunspot numbers each month. So the number of sunspots on the Sun at any time depends on how many have been born lately and have not faded away yet. Looking at a map of the Sun made on Saturday, October 18, I see 17 different sunspots clustered into three close groups. One group is just about to disappear onto the far side. It is likely that these sunspots will fade away before they make it back onto our side again, about the date of November 3.

From what I have said above, you probably guessed that making maps of the Sun is sort of like making maps of clouds: the maps change and you will need to make a new map very soon. And a new map of the Sun is made every day, for the special purpose of counting the number of sunspots. (These maps are made at special telescopes because it is dangerous to look at the Sun with your eyes.) For over 150 years, observers have recorded the number of sunspots they found on the Sun on each day. Some days there were no sunspots, and some days there were as many as 200 sunspots! The Sun has times when sunspots are born often, and the number found might be very high. These times are called Solar Maximum and that happens every 11 years or so. The last Solar Maximum was in 1989, so the next one should be in the year 2000. At Solar Maximum, there will be up to 200 sunspots on the Sun at one time. How big is a sunspot? Sunspots look like tiny specks on the Sun, but that is because the Sun itself is so BIG. (Really, really big).

In a medium-large sunspot (they come in many sizes) the dark middle region (called the umbra) measures about 10,000 miles across. This is wider than the Earth, and three times bigger than the distance from New York to Los Angeles. A really big sunspot can be up to 30,000 miles across, and a whole group of sunspots can be 100,000 miles long. You may be interested in seeing a Web site where daily maps of sunspots are made. This site shows the daily sunspot drawing observations at Mt. Wilson Observatory. .................................. More about sunpots, from Amara Graps. Some people hope to predict sunspots, but for now, predicting sunspots is a little like trying to predict the weather. If are interested in daily sunspot numbers for any time in history back to the year 1818, you can find them at the Sunspot Index Data Center (SIDC) in Belgium, which is the world data center for sunspot index of daily sunspot numbers. If you would like to learn more about how big are the features of the Sun, you may jump to the Solar Center's Web page of comparison activities.

We also have a selection of Web pages for measuring the Sun's rotation using sunspots ( and race your friends ! ), and for learning how Galileo knew that the sunspots were on the Sun.

Question: Visible sunspots vary in number according to a cycle of how many years?
Answer: Eleven