We present a measurement of the accretion disk size of the quadruple lensed quasar HE 0435–1223 from well-sampled 13-year COSMOGRAIL optical light curves. Using accurate time delays for the images A, B, C, and D, we modeled and removed the intrinsic quasar variability, and found microlensing events of amplitude up to 0.6, 0.4, and 0.5 mag in the

Digital tools are increasingly used in cultural astronomy, so that it is now more important than ever to assess their precision and reliability, and to identify what uncertainties they may introduce. The present work aims to address these issues by comparing a dataset of orientations of Roman cities in the Iberian Peninsula measured in situ with

Discovery of the true nature of the halo of the Galaxy has long been limited by the number of stars with available spectroscopy and photometry. This constraint will soon be lifted. While undertaking a thorough spectroscopic follow-up of ~ 1,000,000 extragalactic sources, the Sloan Digital Sky Survey (SDSS) will ALSO obtain spectra of as many as ~

The Hubble constant can be measured from the time delay between pairs of components of a multiply-imaged quasar, depending only on the mass model and the distances to the lens and background source. For a well-determined lens model, H_0 is implicitly related to the observable parameters by H_0 propto sigma_nu^2 Delta tau^{-1}, where sigma_nu is a

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The amplitudes of the Evershed flow are measured using pairs of carefully selected Fe i and Fe ii spectral lines that are close in wavelength and registered simultaneously. A sunspot belonging to the NOAA 11582 group was scanned using the spectrograph of the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). Velocities were extracted