During 1986–1989 at the high-altitude station on the Peak Terskol, Caucasus (h = 3000 m) absolute measurements of the solar disk-centre intensity were performed. The observations were carried out with the specialized solar telescope (D = 23 cm,F = 3 m) and grating spectrometer (F = 2 m, grating 140 × 150 mm, 600 grooves mm−1). The ribbon tungsten lamps used for absolute calibration were calibrated to the USSR standard of spectral intensity and were also compared with the irradiance standard of the PMO/WRC (Davos, Switzerland), with the lamps used in the Alma-Ata Observatory (Kazakhstan) and in Simferopol University for absolute measurements of stellar spectra. Methods and apparatus were improving step by step during 1985–1988. Special care was paid to the study of all possible sources of errors, in particular to the method of correction for atmospheric extinction, to polarization properties of optical elements of the apparatus, and to establishing the most reliable absolute calibration system. Finally, the observations performed during 1989 utilized only the refined methods and apparatus. As a result, the absolute integrals of the solar disk-centre intensity for 1-nm wide spectral bands in the range 310–685 nm are available. We estimate the total error is 2.5% at 310 nm and 2.1% at 680 nm. The absolute irradiance for 5-nm wide spectral bands is also obtained. We compare our results with results by Neckel and Labs (1984), with the irradiance filter measurements performed in PMO/WRC and calibration of the Sun's spectral irradiance to the stellar irradiance standard Vega by Lockwood (1992). Our results show a systematic difference with data by Neckel and Labs in the near-ultraviolet. The results by Neckel and Labs are probably underestimated in this spectral range by 8%.

New absolute measurements of the solar spectrum 310–685 nm

Excited-state populations of energy acceptors are determined for arbitrary and time-varying relationships between the transfer probability and natural excited-state lifetimes of energy donors and acceptors for an arbitrary pump spectrum using cw and pulsed excitation. Various familiar limiting situations are particular cases of the general situation under discussion. The theoretical results were verified experimentally for a Y3Al5O12:Cr3+:Nd3+ crystal. Quantitative agreement was obtained between theory and experiment. The method developed can be used to calculate the improvement in the excited-state population of the lasing particles as a result of sensitization in doubly activated media for solid-state lasers.

Luminescence sensitization and its application to enhance the efficiency of solid-state laser active media

An extended and horizontally homogeneous cloud of a large optical thickness and a weak absorption compared with scattering is considered. The strict analytical formulas for determination of a single-scattering albedo and an optical thickness of this cloud are derived from the strict solution of the radiation transfer equation. These formulas allow retrieving the optical cloud parameters from the reflected or transmitted spectral radiation measurements. A detailed error analysis of the proposed method is carried out. The obtained formulas are applied to the ground-based spectral measurements of the transmitted radiance. The spectral values of the single-scattering albedo and the optical thickness are obtained.

Optical Cloud Characteristics Derived from Measurements of Reflected or Transmitted Solar Radiation

Global changes of zonal cloud structure on Jupiter have been observed and analyzed from data obtained with a 1-m telescope and a low-dispersion spectrograph in the spectral range λλ 400-680 nm, and with a 70-cm telescope and planetary three-channel spectrometer in the spectral range λλ 320-1100 nm during each Jovian apparition from 1988 to 1992. Variations of the observed meridional intensity profiles and relative spectrophotometric gradients are described as well as the changes of absolute spectral reflectivity of five main belts on Jupiter (North and South Equatorial belts, North and South Tropical zones, and Equatorial region)

Spectrophotometry of zonal cloud structure variations on Jupiter, 1988–1993

Phase effect for the brightness coefficient of the central disk of Saturn and features of Jupiter's disk

Available data on the solar energy flux and its spectral components are reviewed and critically analyzed. On the basis of extensive measurement data obtained by various methods, it is shown that the most reliable value of the solar constant is 195 cal/sq cm-sec (or 136 mWt/sq cm). Weighted-mean data on the energy distribution in the solar spectrum from 1400 A to 0.3 mm are presented. Among the topics studied are: the attenuation of radiation in the Earth's atmosphere, instrument probiems in absolute spectrophotometry, the influence of limb darkening of the soiar disk on the energy distribution in the solar spectrum, and the energy distribution in the spectrum of the solar photosphere. (IAA)

A.V. Kharitonov

Papers

Solar constant and the energy distribution in the solar spectrum