Abstract Information theory is used to characterize the solar active region periodicities and memories from Carrington map images 1974–2021. The regions typically evolve move one next. In order track these structures in sequences of images, an innovative method based on information developed. Image entropy provides a measure organization images. can also be as filter identify partition regions,...

We have obtained echelle spectra with the Hubble Space Telescope (HST) of the MgII 2800 Å region of ten stars whose metallicities range from 1/300 to 1/3 that of the Sun, and whose space velocities suggest a halo or old thick-disk origin. Spectra of all ten show doublepeaked emission in the MgII core, very much like the quiet Sun. A halfdozen apparently non-rotating stars were observed more tha...