The Sun as a Variable Star: Solar and Stellar Irradiance Variations Proceedings of the 143rd Colloquium of the International Astronomical Union held in the Clarion Harvest House, Boulder, Colorado, June 20–25, 1993

The IAU Colloquium No. 143 "The Sun as a Variable Star: Solar and Stellar Irradiance Variations" was held on June 20 - 25, 1993 at the Clarion Harvest House, Boulder, Colorado, USA. The main objective of this Colloquium was to review the most recent results on the observations, theoretical interpreta­ tions, and empirical and physical models of the variations observed in solar and stellar irradiances. A special emphasis of the Colloquium was to discuss the results gained on the climatic impact of solar irradiance variability. The study of changes in solar and stellar irradiances has been of high interest for a long time. Determining the absolute value of the luminosity of stars with different ages is a crucial question for the theory of stellar evolu­ tion and energy production of stellar interiors. Observations of the temporal changes of solar and stellar irradiances - in the entire spectral band and at different wavelengths - provide an additional tool for studying the physical processes below the photosphere and in the solar- stellar atmospheres. Since the Sun's radiative output is the main driver of the physical processes with­ in the Earth's atmosphere, the study of irradiance changes is an extremely important issue for climatic studies as well. Climatic models show that small, but persistent changes in solar irradiance may influence the Earth's climate.

Preface. Cryogenic Solar Absolute Radiometer -- CSAR. A Review of the Nimbus-y ERB Solar Dataset. Long-Term Variations in Total Solar Irradiance. Solar Total Irradiance Variability from SOVA 2 on Board EURECA. The Periodicity of Solar Activity Cycles. Maximum and Minimum Temperatures at Armagh Observatory 1844--1992, and the Length of the Sunspot Cycle. Photometer `DIFOS' for the Study of Solar Brightness Variations. The Brightness of the Solar Disk in tne Continuum in the Region 1.0--2.4 mum. Irradiance Observations of the 1--8 Å Solar Soft X-Ray Flux from GOES. Comparisons of the Mg II Index Products from the NOAA-9 and NOAA-aa SBUV/2 Instruments. The Solar Ca II K Index and the Mg II Core-to-Wing Ratio. Solar EUV Flux Variations near Activity Maxima. The X-Ray-EUV Spectrum of Optically Thin Plasmas. List of Stars Recommended as Spectrophotometric Standards. Variable Stars with the Hipparcos Satellite. Variation of the Solar Diameter from Solar Eclipse Observations, 1715--1991. Latitudinal Variation of the Solar Limb-Darkening Function. Improvement of the Photometric Sunspot Index and Changes of the Disk-Integrated Sunspot Contrast with Time. Modelling Solar Irradiance Variations with an Area-Dependent Photometric Sunspot Index. On the Cause of Total Irradiance Variations Observed by the CCD Solar Surface Photometer. Latitude and Cycle Variations of the Photospheric Network. Variability of the Solar Chromospheric Network over the Solar Cycle. A YOHKOH Search for `Black-Light Flares'. Coronal Index of Solar Activity: Years 1939--1963. Rotational Characteristics of the Green Solar Corona: 1964--1989. Solar Cycle Variation of the Microwave Spectrum and Total Irradiance. Solar Brightness Distribution and its Variability at 3 Millimeter Wavelength. Latitudinal Variability of Large-Scale Coronal Temperature and its Association with the Density and the Global Magnetic Field. Active Region Evolution and Solar Flux Variations. On theVariability of Some Characteristics of Solar Radiative Flux. Lyman-Alpha Line Intensity as a Solar Activity Index in the Far Ultraviolet Range. Modeled Soft X-Ray Solar Irradiances. Cosmic Rays as an Indicator of Solar Activity. Meridional Motions of Sunspot Groups during Eleven Activity Cycles. Radiation-Hydrodynamic Waves and Global Solar Oscillations. Excitation of Solar Gravity Waves. Solar Noise Simulations in Irradiance. Secular Variations in the Spectrum of Solar P-Modes. Solar Cycle Variations in P-Modes and Chromospheric Magnetism. Sunspot Number Uncertainties and parametric Representations of Solar Activity Variations. `Star as a Sun' Observations in Seismology of Distant Stars. Rotating Convection and the Solar Differential Rotation. Variations of the Magnetic Fields of the Sun and the Earth within 7--50 Day Periods. Distinction between the Climatic Effects of the Solar Corpuscular and Electromagnetic Radiation. A Space Project for Solar Oscilliations and Long-Term Variability relevant to Climatic Changes. Solar Magnetic and Bolometric Cycles recorded in Sea Sediments. Long-Term Persistence of Solar Activity (Abstract). Stellar Irradiance Variations due to Surface Temperature Inhomogeneities (Abstract). Voyager EUV Solar Spectra during 1981--1993 (Abstract). On P-Mode Oscillations in Stars from 1M⊙ to 2M⊙ (Abstract). Facular Excess Radiation and the Energy Balance of Solar Active Regions (Abstract). The 73-Day Periodicity of the Flare Index during the Current Solar Cycle 22 (Abstract). Phase Differences between Irradiance and Velocity Low-Degree Solar Acoustic Modes Revisited (Abstract).