Sunspots are planet-sized concentrations of magnetic flux on the surface of the sun; they are sources of solar flares, coronal mass ejections and intense UV radiation.
They are cooler (and thus darker) regions on the sun where the magnetic field loops up out of the solar surface. Sunspots generally occur in pairs of opposite polarity.
Essentially, a magnetic storm on the the Sun's surface which appears as a dark area. A sunspot is approximately 1,500 to 2,500 degrees Kelvin cooler than the surrounding photosphere. The number of sunspots we see on the Sun at any given time appears to cycle every 11 years.
Solar radiationLast Updated on 2010-01-24 19:11:07
Almost all of the energy that drives the various systems (climate systems, ecosystems, hydrologic systems, etc.) found on the Earth originates from the sun (Figure 1). Solar energy is created at the core of the sun when hydrogen atoms are fused into helium by nuclear fusion (Figure 2). The core occupies an area from the sun’s center to about a quarter of the star’s radius. At the core, gravity pulls all of the mass of the sun inward and creates intense pressure. This pressure is high enough to force the fusion of atomic masses.
For each second of the solar nuclear fusion process, 700 million tons of hydrogen is converted into the heavier atom helium. Since its formation 4.5 billion years ago, the sun has used up about half of the hydrogen found in its core. The solar nuclear process also creates immense heat that causes atoms to discharge photons.... More »
How Low Can It Go? Sun Plunges into the Quietest Solar Minimum in a CenturyLast Updated on 2009-04-01 00:00:00April 1, 2009: The sunspot cycle is behaving a little like the stock market. Just when you think it has hit bottom, it goes even lower.
2008 was a bear. There were no sunspots observed on 266 of the year's 366 days (73%). To find a year with more blank suns, you have to go all the way back to 1913, which had 311 spotless days: plot. Prompted by these numbers, some observers suggested that the solar cycle had hit bottom in 2008.
Maybe not. Sunspot counts for 2009 have dropped even lower. As of March 31st, there were no sunspots on 78 of the year's 90 days (87%).
It adds up to one inescapable conclusion: "We're experiencing a very deep solar minimum," says solar physicist Dean Pesnell of the Goddard Space Flight Center.
"This is the quietest sun we've seen in almost a century," agrees sunspot expert David Hathaway of the Marshall Space Flight Center.
Above: The sunspot cycle from 1995 to... More »
Sunspots: 17th CenturyLast Updated on 2007-11-26 00:00:00
Using telescopes similar to Galileo Galilei’s instrument, Johannes Fabricius and Christoph Scheiner began the first systematic study of sunspots in early 1611. Johannes Fabricius was the first to publish his observations in De Maculis in Sole Observatis ("On the Spots Observed in the Sun") in 1611, but it remained unknown to the other observers for some time. Scheiner’s book Tres Epistolae de Maculis Solaribus Scriptae ad Marcum Welserum ("Three Letters on Solar Spots written to Marc Welser") appeared in 1612.
Scheiner wanted to preserve the unblemished perfection of the sun, and proposed that sunspots were simply satellite orbiting the sun. In 1612, Galileo was equally certain that sunspots were on the surface of the sun, or at least that they could be clouds in the solar atmosphere, and published his first drawings of them in his 1613 book Istoria e Dimostrazioni intorno... More »
Sunspots: First ObservationsLast Updated on 2007-11-26 00:00:00
The two oldest written records of a sunspot observation are found in the Book of Changes, probably the oldest extant Chinese book, compiled in China around or before 800 BC. The text reads "A dou is seen in the Sun", and "A mei is seen in the Sun." From the context, the words (i.e., chinese characters) "dou" and "mei" are taken to mean darkening or obscuration.
Astronomers at the court of the Chinese and Korean emperors made regular notes of sunspots, most less elliptical than the one cited above. It seems, however, that observations were not carried out systematically for their own sake, but instead took place whenever astrological prognostication was demanded by the emperor. The surviving sunspots records, though patchy and incomplete, covers nearly 2000 years and represents by far the most extensive pre-telescopic sunspot record. 
The earliest known drawing of sunspots appears... More »
Sunspots: CycleLast Updated on 2007-11-26 00:00:00
In the mid-1800s astronomers discovered from hundreds of sunspot sightings that, when they tabulated and graphed them, their numbers increased and decreased over time in a repeatable cycle. These extremes represent the amplitude of the cycle. We now call this the solar activity cycle or the sunspot cycle. Heinrich Schwabe published his first measurements of the sunspot cycles between 1826-1843 in 1843. He had counted these spots every possible clear day, and found two peaks in 1828 and 1837, with minima in 1833 and 1843. Subsequent historical studies by astronomers such as Rudolph Wolf uncovered recognizable cycles since 1700. A curious absence of cyclic behavior was noted by Gustav Spörer to the dawn of telescopic observations in ca 1610. This period is known as the Maunder Minimum, which coincides with an unusually cool period in European history called the Little Ice Age. Further... More »
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