The observation of redshift-dependent coherent orientations of quasar polarisation vectors over cosmological distances in some regions of the sky is reviewed. Based on a good-quality sample of 355 measured quasars, this observation seems to infer the existence of a new effect acting on light propagation on such huge distances. A solution in terms of nearly massless axion-like particles has been...

We present a simple algorithm for identifying periods of time with broadband GHI similar to that occurring during clear sky conditions from a time series of global horizontal irradiance (GHI) measurements. Other available methods to identify these periods do so by identifying periods with clear sky conditions using additional measurements, such as direct or diffuse irradiance. Our algorithm com...

We present a characterization of two narrow band lters commonly used in Infrared Astronomy. Our study mainly quantiies the eeect of temperature and tilt angle on the central wavelength and width of the transmission bands of such lters. This allows to evaluate some important eeects that must be taken into account to have good quality astronomical images. EEects as the limitation of the eld of vi...

One of the three major goals of the Atmospheric Radiation Measurement (ARM) Program is to improve the quality of radiation models under clear sky, homogeneous cloud, and broken cloud conditions. This report is concerned with the development of the theory of radiation transfer in the broken clouds. Our approach is based on a stochastic description of the interaction between the radiation and clo...

Ongoing observations of the Cosmic Microwave Background, such as the MAXIMA and BOOMERanG projects, are providing datasets of unprecedented quality and ever-increasing size. Exact analysis of the data they produce is a serious computational challenge, currently scaling as the number of sky pixels squared in memory and cubed in time. Here we discuss the origins of these scaling relations and the...