Diagram of sun, showing the progress of sunspot activity, the course of the solar maculae over the sun's disk. Engraving by Seale, second half of 18th century. 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 of opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.

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Sunspot Activity, 18th Century

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Keywords: 18th, activity, art, astronomy, bw, century, diagram, disk, engraving, history, illustration, maculae, observation, phemomena, progress, science, seale, showing, solar, spots, sun, sunspot