A flux of EUV emission measured on-board the “CORONAS” artificial satellites near minimum and maximum of the 23rd cycle of solar activity

This comparison demonstrated that X-ray emission measured on-board the GOES spacecraft and measured due to SUVR instrument (with filters in wave-range <12 nm) changed almost synchronously in the ranges 0.1-0.8 and 0.1-12 nm. The data measured due to VUSS showed that EUV emission appeared a few minutes (1-13) before X-ray emission. Apparently it evidences that at first a flare begins in the chromosphere and then a heating area is spreading higher. Solar emission increases by ∼20-30% in the range λ < 130 nm, and only by 8-10% in EUV range. Changes of extreme ultraviolet (EUV) solar flux were registered during the annular solar eclipse of May 31, 2003, when the CORONAS-F satellite thrice intersected a zone of the solar eclipse.