Butterfly Diagram and Other Properties of Plage Areas from Kodaikanal Ca ii K Photographs Covering 1904 - 2007.

Ca ii K observations of the Sun have a great potential for probing the Sun's magnetism and activity, as well as for reconstructing solar irradiance. The Kodaikanal Solar Observatory (KoSO) in India, houses one of the most prominent Ca ii K archives, spanning from 1904 to 2007, obtained under the same experimental conditions over a century, a feat very few other sites have achieved. However, the KoSO Ca ii K archive suffers from several inconsistencies (e.

Sun-like stars produce superflares roughly once per century.

Stellar superflares are energetic outbursts of electromagnetic radiation that are similar to solar flares but release more energy, up to 10 erg on main-sequence stars. It is unknown whether the Sun can generate superflares and, if so, how often they might occur. We used photometry from the Kepler space observatory to investigate superflares on other stars with Sun-like fundamental parameters.

Metal-rich stars are less suitable for the evolution of life on their planets.

Atmospheric ozone and oxygen protect the terrestrial biosphere against harmful ultraviolet (UV) radiation. Here, we model atmospheres of Earth-like planets hosted by stars with near-solar effective temperatures (5300 to 6300 K) and a broad range of metallicities covering known exoplanet host stars. We show that paradoxically, although metal-rich stars emit substantially less ultraviolet radiation than metal-poor stars, the surface of their planets is exposed to more intense ultraviolet radiation.

The Sun is less active than other solar-like stars.

The magnetic activity of the Sun and other stars causes their brightness to vary. We investigated how typical the Sun's variability is compared with other solar-like stars, i.e.

Publisher's Note: Solar Irradiance Variability is Caused by the Magnetic Activity on the Solar Surface [Phys. Rev. Lett. 119, 091102 (2017)].

This corrects the article DOI: 10.1103/PhysRevLett.119.

Solar Irradiance Variability is Caused by the Magnetic Activity on the Solar Surface.

The variation in the radiative output of the Sun, described in terms of solar irradiance, is important to climatology. A common assumption is that solar irradiance variability is driven by its surface magnetism. Verifying this assumption has, however, been hampered by the fact that models of solar irradiance variability based on solar surface magnetism have to be calibrated to observed variability.

Millennium-scale sunspot number reconstruction: evidence for an unusually active sun since the 1940s.

The extension of the sunspot number series backward in time is of considerable interest for dynamo theory, solar, stellar, and climate research. We have used records of the (10)Be concentration in polar ice to reconstruct the average sunspot activity level for the period between the year 850 to the present. Our method uses physical models for processes connecting the (10)Be concentration with the sunspot number.

Intercalibration of SUMER and CDS on SOHO. III. SUMER and CDS-GIS. Solar and Heliospheric Observatory.

Simultaneous observation of the same solar sources with different instruments is one way to test prelaunch radiometric calibrations and to detect changes in responsivity with time of extreme-ultraviolet instruments in space. Here we present the results of intercalibration of the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrometer (detectors A and B) and the GIS (Grazing Incidence Spectrometer), one of two spectrometers that compose the CDS (Coronal Diagnostic Spectrometer) on the Solar and Heliospheric Observatory (SOHO). The two instruments observed simultaneously radiances of emission lines at or near the center of the solar disk.