We present numerical experiments aimed at understanding why near-infrared observations systematically deliver weak magnetic fields in the internetwork, whereas analyses based on visible lines indicate that kG fields are ubiquitous. Synthetic noisy Stokes V profiles of the iron lines at 6302 Å and 1.565 mu m have been produced under varying

Recording tracks of stars traversing the field of view of the Auger's fluorescence detector (FD) is a powerful to ol to monitor various FD parameters. For instance, the telescope absolute pointing and its stability during the life of the experiment, the sky quality and the uniformity of the photo catho des response, are good examples. Regular

The Whole Earth Blazar Telescope (WEBT) is an international consortium of about 30 optical observatories and 2 radio observatories devoted to blazar monitoring during optical and multifrequency campaigns. The dispersion in longitude of the WEBT members allows them to obtain dense and quasi-continuous light curves, minimizing gaps due to Earth

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