The first entry related to SSN directs the reader to a document titled "Readme: Sunspot Numbers" in which it is written : "The SunSpot Number (SSN) is a commonly used index of solar activity. The daily sunspot number was first introduced in 1848 by the Swiss astronomer, Johann Rudolph ...
Sunspot, vortex of gas on the surface of the Sun associated with strong local magnetic activity. Spots look dark only by contrast with the surrounding photosphere, which is several thousand degrees hotter. The dark centre of a spot is called the umbra; t