The population of high-energy and very high-energy γ-ray sources, detected with EGRET and the new generation of ground-based Cherenkov telescopes, forms a reduced but physically important sample. Most of these sources are extragalactic (e.g. blazars), while among the galactic ones there are pulsars and supernova remnants. The microquasar LS 5039

It is essential to properly calibrate the polarimetric properties of telescopes, if one wants to take advantage of the capabilities of high precision spectro-polarimeters. We have constructed a model for the German Vacuum Tower Telescope (VTT) that describes its time-dependent polarization properties. Since the coelostat of the telescope changes

Stellar population synthesis models are crucial for the understanding of the large amount of data which is being gathered for galaxies at low and high redshift, and provide the only way to compare the ``real world'' with the theoretical framework. The best models require extensive empirical stellar spectral libraries, which at present are starting

We use visible and submm polarimetric data to trace, study and compare magnetic fields within and near elongated molecular clouds. A preliminary polarimetric map of OMC-2 at 850 μm is presented. With other published results, these new measurements will lead to detailed representations of how the magnetic field threading the filaments connects to

Traditionally the earth's reflectance has been assumed to be roughly constant, but large decadal variability, not reproduced by current climate models, has been reported lately from a variety of sources. We compare here the available datasets related to earth's reflectance, in order to assess the observational constraints on the models. We find a

Galactic black holes release an unknown fraction of their accreting matter and energy in the form of collimated outflows (or jets) that travel into the surrounding medium. Black Hole X-ray Binaries (BHXBs) are the essential laboratories for understanding the overall physics of the accretion process in these systems, and have provided us with a