Solar activity graph over the last 400 years

Spectral intensity of solar energy flux ^d∕_dν (^dP∕_dS) is measured at a wavelength of 10.7 cm since year 1947. It is used as one of the solar activity indexes – F10.7 (10.7-cm [Radio] Flux).

In earlier years only one (indirect) method of the solar activity estimating was used – sunspot number counting. – Relative sunspot number (Wolf number, W) is another (old) solar activity index.

For years before 1947 F10.7 is calculated here from the relative sunspot number (for the XVII century – just from the number of sunspots).

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