The paper analyzes white-light images of solar granulation taken outside active regions, at regular intervals along the polar axis and the equator, in order to study its center-to-limb variation and possible changes with the solar latitude. The 2D spatial power spectra of the brightness distribution are calculated and corrected for the distortions

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We have compiled all the available optical B band data on OJ287, between 1890 and 1991. Using this data we have found a period of 11.6 +/- 0.5 yr for the outbursts in OJ 287. This value is in good agreement with the period of 11.65 yr between outbursts and 11.05 yr between minima found previously by Sillanpaa et al. (1988), using V-band data. Based

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We are living a renaissance of radio survey work: the size of source catalogues published in the first two years of this decade exceeds that of the entire 1980s! The total number of published flux densities in mid-1992 is probably nearing ~700,000 and is estimated to grow by a factor of four by the end of the decade. The number of known optical

We have used three large-scale radio surveys to study the spectral behaviour of radio sources towards Abell clusters of galaxies. Without attempting to separate genuine cluster sources from background sources, we find a steeper median spectral index within 0.5 Abell radii (r_A_) than between 0.5 and 1 r_A_ (1 r_A_=3 h_50^-1 Mpc, and H_0 = 50 h_50_