Variations in the H Ly alpha intensity in solar activity cycles from measurements onboard satellites and rockets

Data on radiation intensity of the Sun's Lyman-alpha hydrogen line (lambda= 121.6 nm) for a maximum and minimum of solar activity are considered. Resul ts of longterm measurements, received onboard 5 American and 9 Russian sate llites and space vehicles for a period from 1969 till 1998, as well as data of numerous rocket measurements, since 1955 are analyzed. Radiation of the quiet Sun (without flares) in the L alpha line differs between phases of a solar activity cycle and changes from cycle to cycle were observed. Radiation intensity at the minimum of a solar activity cycle varies from (2 .25 - 4.3).10(11) cm(-2)s(-1) for activity minimum to (6.1 - 9).10(11) cm(- 2)s(-1) for a maximum of a cycle. (C) 2000 Elsevier Science Ltd. All rights reserved.