Figure 15: Energy spectra of protons at 1 AU during quiet Sun according to understanding in 1970s (a) and at present (b). 1: solar wind, 2: suprathermal particles, 3: energetic particles of solar origin, 4: galactic cosmic rays. One of the tasks of the Prognoz-3 satellite consisted of measurements of particle flux at energies as close as possible to the energies of solar wind particles. The experiment conducted allowed to measure spectra during the quietest periods within the active interval of Prognoz-3. Energy spectra were measured down to 30 keV and the minimum of the proton flux was found. Presently it is clearly confirmed that there are no peculiarities in the energy spectra of particles in the energy range between energetic particles (<1 MeV) and solar wind. The energy spectra of protons measured in quiet time period of the Sun according to recent observations are shown in (b).