A study of variations of solar spectral irradiance (SSI) in the wavelength ranges 121.5 nm-300.5 nm for the period 1981-2009 is presented. We used various data for ultraviolet (UV) spectral lines and international sunspot number (ISSN) from interactive data centers such as SME (NSSDC), UARS (GDAAC), SORCE (LISIRD) and SIDC, respectively. We reduced these data by using the MATLAB software package. In this respect, we revealed negative correlations of intensities of UV (289.5 nm-300.5 nm) spectral lines originating in the solar chromosphere with the ISSN index during the unusually prolonged minimum between the solar activity cycles (SACs) 23 and 24. We also compared our results with the variations of solar activity indices obtained by the ground-based telescopes. Therefore, we found that plage regions decrease while facular areas are increasing in SAC 23. However, the decrease in plage regions is seen in small sunspot groups (SGs), contrary to this, these regions in large SGs are comparable to previous SACs or even larger as is also seen in facular areas. Nevertheless, negative correlations between ISSN and SSI data indicate that these variations are in close connection with the classes of sunspots/SGs, faculae and plage regions. Finally, we applied the time series analysis of spectral lines corresponding to the wavelengths 121.5 nm-300.5 nm and made comparisons with the ISSN data. We found an unexpected increase in the 298.5 nm line for the Fe II ion. The variability of Fe II ion 298.5 nm line is in close connection with the facular areas and plage regions, and the sizes of these solar surface indices play an important role for the SSI variability, as well. So, we compared the connection between the sizes of faculae and plage regions, sunspots/SGs, chemical elements and SSI variability. Our future work will be the theoretical study of this connection and developing of a corresponding model.

Four series of coronal images have been obtained by the expedition of Abastumani Astrophysical Observatory during the August 11, 1999 total solar eclipse with the help of a photographic mirror -lens polarimeter (D = 100 mm, F = 1000 mm). Each series include three images corresponding to three positions of the polarization analyzer. The position of the solar disk center relative to the Moon's center has been determined beforehand. In addition, the background skylight polarization and intensity are calculated. All measurements are absolute given in units of the Sun's average surface brightness. A new technique for separation of the F-and K-coronae is used. It was found that in the equatorial regions the model of hydrostatic distribution of the density with T = constant is not quite accurate for the August 11, 1999 corona and there is a temperature gradient in this region. For r 1 = 1.3R and r 2 = 1.8R we derived T 1 = 1.25 × 10 6 K and T 2 = 1.07 × 10 6 K, respectively. The average polarization degree in the equatorial regions changes from 10 to 40%, while in the polar regions the maximum value reaches only 10%. The values of electron densities N e (r) vary from 1.32 × 10 8 cm −3 (r = 1.1R ) to 2.0 × 10 6 cm −3 (r = 2.0R ). Our data are compared with previous measurements.

Four series of coronal images have been obtained by the expedition of Abastumani Astrophysical Observatory during the August 11, 1999 total solar eclipse with the help of the photographic mirror-lens polarimeter (D=150 mm, F=1000 mm). Each series includes three images corresponding to three positions of the polarization analyzer. The position of the solar disk center relative to the Moon's center has been determined beforehand. In addition, the background skylight polarization and intensity are calculated. All measurements are absolute given in units of the sun's average surface brightness. Equatorial electron densities and temperatures are determined. Our data are compared with previous absolute measurements.To search for other articles by the author(s) go to:

Five series of coronal images have been obtained by V.Kulijanishvili during the total solar eclipse of the June 21, 2001, in Zambia, Lusaka. A photographic mirror-lens coronagraphpolarimeter (D=100 mm, F=1000 mm) was used. The absolute brightness, polarization and direction of polarization of the inner corona were measured. Standard techniques are used for the separation of the F-and K-coronas and for determination of coronal electron densities and temperatures. The background skylight polarization and intensity are calculated.