Sunspot

Sunspot from Hinode in G band (4305) 2007-04-30 T001456

File:Growing Sunspots Tracking Closeup - February 2011.ogv

Sunspot butterfly graph

File:Sunspot Growth in June 2012.ogv

Power spectrum of sunspot number, from 1945 to 2017

Swedish Solar Telescope

Sunspots are temporary phenomena on the Sun's photosphere that appear as spots darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection. Sunspots usually appear in pairs with opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.

Formation and Characteristics

Sunspots are formed in the Sun's photosphere, the outermost layer of the Sun, and are the visible surface manifestations of magnetic field lines that protrude through the Sun's surface. The magnetic field lines are thought to be generated by the Sun's differential rotation and its convective motion, a process described by the dynamo theory. The intense magnetic activity inhibits the convective transport of heat from the Sun's interior to its surface, resulting in areas of lower temperature and thus darker appearance compared to the surrounding regions.

The size of sunspots can vary, ranging from small spots that are barely visible without the aid of a telescope, to large complexes that can be several times the size of Earth. Sunspots consist of a central dark region called the umbra, surrounded by a lighter region named the penumbra, which exhibits a filamentary structure.

Lifecycle

The lifecycle of a sunspot can vary from a few days to a few months, although the average duration is about two weeks. Sunspots can evolve significantly during their lifecycle, changing in size and shape. They can also merge with other sunspots or split into smaller ones.

Solar Cycle

Sunspots are closely associated with the solar cycle, an approximately 11-year cycle that ranges from solar minimum, with few sunspots, to solar maximum, with many sunspots. During solar maximum, the Sun's magnetic field lines are the most distorted due to the differential rotation of the Sun's equator compared to its poles. This period is also associated with increased solar activity, including solar flares and coronal mass ejections (CMEs), which can have significant effects on Earth's magnetosphere and ionosphere, affecting satellite operations, radio communications, and power grids.

Observation and Impact

Historical records of sunspot observations date back to ancient China, but the scientific study of sunspots began in earnest with Galileo Galilei in the early 17th century, challenging the prevailing Aristotelian cosmology that held the heavens to be perfect and unchanging. Today, sunspots are studied using a variety of instruments, including ground-based telescopes and space-based observatories like the Solar Dynamics Observatory (SDO).

The study of sunspots is important not only for understanding the Sun's magnetic activity and its impact on the solar system but also for its implications for space weather forecasting. Large solar events associated with sunspots can disrupt Earth's magnetosphere, posing risks to satellites, communications systems, and power grids.

See Also

• Solar flare
• Coronal mass ejection
• Magnetosphere
• Solar cycle
• Dynamo theory

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