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Sunspots are a feature of the Sun that have been observed since ancient times. When viewed through a telescope, they have a dark central region known as the umbra, surrounded by a somewhat lighter region called the penumbra. Sunspots are dark because they are cooler than the surrounding photosphere . They are the site of strong magnetic fields. The reason sunspots are cool is not entirely understood, but one possibility is that the magnetic field in the spots inhibits convection underneath them.
Sunspots typically grow over a few days and last anywhere from a few days to a few months. Observations of sunspots first revealed that the sun rotates with a period of 27 days (as seen from Earth). The number of sunspots on the Sun is not constant, but varies with an 11 year period known as the solar cycle. Solar activity is directly related to this cycle.
Sunspots are areas where the magnetic field is about 2,500 times stronger than Earth's, much higher than anywhere else on the Sun. Because of the strong magnetic field, the magnetic pressure increases while the surrounding atmospheric pressure decreases. This in turn lowers the temperature relative to its surroundings because the concentrated magnetic field inhibits the flow of hot, new gas from the Sun's interior to the surface.
Sunspots tend to occur in pairs that have magnetic fields pointing in opposite directions. A typical spot consists of a dark region called the umbra, surrounded by a lighter region known as the penumbra. The sunspots appear relatively dark because the surrounding surface of the Sun (the photosphere) is about 10,000 degrees F., while the umbra is about 6,300 degrees F. Sunspots are quite large as an average size is about the same size as the Earth.
Sunspots, Solar Flares, Coronal Mass Ejections and their influence on Earth
Coronal Mass Ejections (shown left) and solar flares are extremely large explosions on the photosphere. In just a few minutes, the flares heat to several million degrees F. and release as much energy as a billion megatons of TNT. They occur near sunspots, usually at the dividing line between areas of oppositely directed magnetic fields. Hot matter called plasma interacts with the magnetic field sending a burst of plasma up and away from the Sun in the form of a flare. Solar flares emit x-rays and magnetic fields which bombard the Earth as geomagnetic storms. If sunspots are active, more solar flares will result creating an increase in geomagnetic storm activity for the Earth. Therefore during sunspot maximums, the Earth will see an increase in the Northern and Southern Lights and a disruption in power grids and radio transmissions. The storms can even change polarity in satellites which can damage sophisticated electronics.
But the jury is still out on how much sunspots can (or do) affect the Earth's climate. Times of maximum sunspot activity are associated with a very slight increase in the energy output from the sun. Ultraviolet radiation increases dramatically during high sunspot activity, which can have a large effect on the Earth's atmosphere. From the mid 1600s to early 1700s, a period of very low sunspot activity (known as the Maunder Minimum) coincided with a number of long winters and severe cold temperatures in Western Europe, called the Little Ice Age. It is not known whether the two phenomena are linked or if it was just coincidence. The reason it is hard to relate maximum and minimum solar activity (sunspots) to the Earth's climate, is due to the complexity of the Earth's climate itself. For example, how does one sort out whether a long-term weather change was caused by sunspots, or maybe a coinciding El Nino or La Nina? Increased volcanic eruptions can also affect the Earth's climate by cooling the planet. And what about the burning of fossil fuels and clear cutting rain forests? One thing is more certain, sunspot cycles have been correlated in the width of tree ring growth. More study will be conducted in the future on relating sunspot activity and our Earth's climate.
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