Photospheric and chromospheric solar magnetograms sometimes show opposite polarity. This intriguing phenomenon is associated with the emergence of magnetic flux and with nearby, but not necessarily superposed, flaring activity. Despite the fact that there may be different explanations, it is shown here that the observed reversals are consistent

Optical imaging and spectroscopy reveal that the ionised region No.252 in the list of Marsalkowa (1974Ap&SS..27....3M), whose photograph is presented in the ``Atlas of Galactic Nebulae'' by Neckel & Vehrenberg (1990), is actually a planetary nebula. According to Acker et al. (1992ESOPN...1....1A), the object should therefore be named as PN G321.6

In an Omega 0 = 1 universe, within the classical Eulerian theory of gravitational instability, the redshift evolution of a peculiar velocity field in a region with arbitrary initial density contrast is derived, for the first time, in real space and third-order perturbation theory. A vector proportional to the gravitational acceleration can also be

We present a light curve of C/1995 O1 (Hale-Bopp) compiledfrom more than 3000 visual observations of the comet made by members of the The Astronomer Group world-wide. These observations cover the period from discovery through to the end of 1997. The light curve shows that the rate of brightening of the comet varied widely at different times, with

We have obtained I-, J-, H- and K-band light curves of the recurrent nova TCrB. We find that we can fit the J-band light curve only with a Roche lobe filling secondary star and a dark spot of radius 11 deg-26 deg (90 per cent confidence) centred at the inner Lagrangian point. We obtain limits to the binary inclination of 38 deg-46 deg (90 per cent

Line asymmetries and shifts are powerful tools for studying velocity fields in the stellar photospheres. Other effects, however, could also generate asymmetries, blurring the information of the velocity patterns. We have studied the shifts and asymmetries induced in the profiles of spectral lines by pressure effects. The best theoretical and