Microvariability observations of two TeV emitting blazars have been made from the Canary Islands International Observatories since 1990. We present a small sample of typical results from the study. We find that, in contrast to the long-term light curve, Mark 501 is more active than Mark 421, suggesting that these, superficially similar objects, are

We describe a data analysis technique for helioseismology that provides a reduction in the contamination of the solar oscillation spectrum from incoherent noise. We show that the technique allows: (i) a significant improvement in the signal-to-noise ratio for the modes in the oscillation power spectrum, and (ii) the solar velocity background

A description is given of the activities of an international working group created with the aim of obtaining both photometric and astrometric observations of visual double and multiple stars with angular separations in the range of one to fifteen arcseconds, that formed part of the HIPPARCOS Input Catalogue. The scientific aims and realisations of

New calculations of the Galactic contamination over microwave background radiation anisotropies are carried out. On the one hand, when a frequency-dependent contrast of molecular clouds with respect to the Galactic background of the diffuse interstellar medium is taken into account, the anisotropic amplitude produced by Galactic dust is increased

IAUC 7161 available at Central Bureau for Astronomical Telegrams.

The HST snapshot survey of 108 BL Lac objects has revealed several instances of unusual morphologies, three jets and a possible Einstein ring. Of the three detected optical jets, two were already known (PKS 0521-365 and 3C371) and one is a new discovery (PKS 2201+044). At HST resolution the jets are well resolved and individual knots clearly seen