Aims: We estimate the minimum length on which solar granulation can be considered to be a Markovian process. Methods: We measure the variation in the bright difference between two pixels in images of the solar granulation for different distances between the pixels. This scale-dependent data is empirically analyzed to find the minimum scale on which

Context: The space experiment CoRoT has recently detected transits by a hot Jupiter across the disc of an active G7V star (CoRoT-Exo-2a) that can be considered as a good proxy for the Sun at an age of approximately 0.5 Gyr. Aims: We present a spot modelling of the optical variability of the star during 142 days of uninterrupted observations

The active galactic nucleus PG 1553+113 was observed by the MAGIC telescope in July 2006 during a multiwavelength campaign, in which telescopes in the optical, X-ray, and very high energies participated. Although the MAGIC data were affected by strong atmospheric absorption (calima), they were analyzed after applying a correction. In 8.5 h, a

The physics of blazar flares is still not well understood. Currently favored emission models include electron inverse Compton (IC) scattering of low-energy synchrotron photons from within the jet or photons generated outside the jet, emission produced by the proton initiated cascades or synchrotron emission of extremely high-energy protons or muons

The Cherenkov light flashes produced by extensive air showers are very short in time. A high bandwidth and fast digitizing readout, therefore, can minimize the influence of the background from the light of the night sky, and improve the performance in Cherenkov telescopes. The time structure of the Cherenkov image can further be used in single-dish

We present an algorithm (MEAD, for `Mapping Extinction Against Distance') which will determine intrinsic (r' - i') colour, extinction, and distance for early-A to K4 stars extracted from the IPHAS r'/i'/Hα photometric data base. These data can be binned up to map extinction in three dimensions across the northern Galactic plane. The large size of