It is pointed out that the phenomenon of solar rotation is known since the introduction of the telescope into astronomy by Galilei in 1610. Regular measurements concerning the positions of sunspots were conducted with the aid of photographic plates at the Royal Greenwich Observatory during the time from 1874 to 1976. The obtained data provide an

The evidence is noted that (1) a flux density limited complete sample of X-ray emitting BL Lac type sources is now available from Schwartz and Ku (1983), that (2) the radio through X-ray emission of BL Lac type sources is most easily interpreted as nonthermal emission from a relativistically boosted jet pointed close to the line of sight and that

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The age decay of two indicators of the stellar magnetic activity (λ2800 Mg II emission flux and λ10830 He I equivalent width) have been studied for field solar-type stars. The Li abundance has been used, in most of the cases, as a stellar age indicator. A calibrated decay law for Mg II has been determined and compared with a similar one, recently